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The va l id ity o f the EQ-5D-3L items : an invest igat ion w ith type 2 d iabetes pat ients from s ix European
countr ies
Uwe Konerd ing 1* , Sy lv ia G E lkhu izen 2 , Raque l Faube l 3 , Pau l Forte 4 , Tom i Ma lmström 5 , E lp ida Pav i 6 and MF Bas Janssen 7
Abstract
Background :Mos t p rev ious s tud ies conce rn ing the va l id i ty o f the EQ -5D -3L i tems re fe r to app l ica t ions o f on ly a s ing le language ve rs ion o f the EQ -5D -3L in on ly one coun t ry . The re fo re , the re is l i t t le in fo rma t ion conce rn ing the ex ten t to wh ich the resu l ts can be gene ra l ised ac ross d i f fe ren t language ve rs ions and/o r d i f fe ren t coun t r ies . He re the va l id i ty o f the EQ -5D -3L i tems is inves t iga ted fo r s ix d i f fe ren t language ve rs ions in s ix d i f fe ren t coun t r ies . Methods :Da ta came f rom 1341 type 2 d iabe tes pa t ien ts (Eng land : 289 ; F in land : 177 ; Ge rmany : 255 ; G reece : 165 ; the Ne the r lands : 354 ; Spa in : 101 ) . The re la t ionsh ips o f the f ive EQ -5D -3L i tems w i th seven d i f fe ren t tes t va r iab les (age , gende r , educa t ion , p rev ious s t roke , p rob lems w i th hea r t , p rob lems w i th lowe r ex t rem i t ies , p rob lems w i th eyes ) , we re ana lysed fo r each comb ina t ion o f i tem and tes t va r iab le . Fo r each comb ina t ion two log is t ic reg ress ion mode ls w i th the d icho tom ised EQ -5D -3L i tem as dependen t va r iab le we re compu ted . The f i rs t mode l con ta ined the tes t va r iab le and dummy coded coun t r ies as independen t va r iab les , the second mode l add i t iona l ly the te rms fo r the in te rac t ion be tween coun t ry and tes t va r iab le . S ta t is t ica l ly s ign i f ican t be t te r f i t o f the second mode l was taken as ev idence fo r coun t ry spec i f ic d i f fe rences rega rd ing the re la t ionsh ip . When such d i f fe rences cou ld be a t t r ibu ted ma in ly to one coun t ry the ana lyses we re repea ted w i thou t the da ta f rom th is coun t ry . Va l id i ty was inves t iga ted w i th the rema in ing da ta us ing resu l ts o f the f i rs t mode ls .
Resu lts :Due to lack o f va r ia t ion in the Span ish da ta on ly 31 o f the o r ig ina l ly in tended 35 in te rac t ion tes ts cou ld be pe r fo rmed . On ly th ree o f these y ie lded a s ign i f ican t resu l t . In a l l th ree cases the Span ish da ta dev ia ted mos t . W i thou t the Span ish da ta on ly 1 o f the 35 in te rac t ion tes ts y ie lded a s ign i f ican t resu l t . W i th 3 excep t ions , the tendency o f repo r t ing p rob lems inc reased w i th age , fema le gende r , lowe r educa t ion , p rev ious s t roke , hea r t p rob lems , p rob lems w i th lowe r ex t rem i t ies and p rob lems w i th eyes fo r a l l EQ -5D -3L i tems .
Conc lus ion :The resu l ts conce rn ing the Eu ropean Span ish ve rs ion a re amb iguous . Howeve r , the i tems o f the Eng l ish , F inn ish , Ge rman , G reek and Du tch ve rs ions o f the EQ -5D -3L re la te in subs tan t ia l ly the same way to the tes t va r iab les . Mos t ly , these re la t ionsh ips ind ica te the i tems’va l id i ty .
Keywords :Hea l th - re la ted qua l i ty o f l i fe , EQ -5D -3L , Va l id i ty , In te r -coun t ry , Me thodo logy
* Co r respondence :uwe .kone rd ing@un i -bambe rg .de
1
T r imbe rg Resea rch Academy , Un ive rs i ty o f Bambe rg , Bambe rg D -96045 , Ge rmany
Fu l l l is t o f au tho r in fo rma t ion is ava i lab le a t the end o f the a r t ic le
© 2014 Konerd ing et a l . ; l icensee B ioMed Centra l Ltd . Th is is an Open Access art ic le d istr ibuted under the terms o f the
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d istr ibut ion , and reproduct ion in any med ium , prov ided the or ig ina l work is proper ly cred ited . The Creat ive Commons Pub l ic
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art ic le , un less otherw ise stated .
The EQ-5D-3L w i th i ts 153 d i f feren t o f f ic ia l language vers ions and a fur ther 19 language vers ions awa i t ing ap- prova l is curren t ly the mos t w ide ly used pre ference-based ins trumen t for measur ing hea l th re la ted qua l i ty o f l i fe [1-4 ] . The EQ-5D-3L cons is ts o f (1 ) a descr ip t ive sys tem compr is ing f ive ques t ionna ire i tems and (2 ) a v isua l ana logue sca le . The ques t ionna ire i tems address f ive d i f- feren t d imens ions o f hea l th : (1 ) mob i l i ty ; (2 ) se l f-care ; (3 ) usua l ac t iv i t ies ; (4 ) pa in/d iscom for t ; and (5 ) anx ie ty/de- press ion . Three answer ca tegor ies are prov ided for each i tem w i th the f irs t ca tegory re ferr ing to the bes t s ta te . The EQ-5D-3L can be app l ied for two purposes : descr ib ing hea l th s ta tes ; and cons truc t ing ind ices wh ich represen t the u t i l i t ies o f these hea l th s ta tes . Severa l scor ing func- t ions for ass ign ing u t i l i t ies to hea l th s ta tes are ava i lab le and mos t o f these re fer to one spec i f ic language vers ion o f the EQ-5D-3L [5 ] .
Wha tever purpose the EQ-5D-3L i tems are used for , they need to be va l id . Th is means , in the f irs t ins tance , tha t they shou ld adequate ly descr ibe the responden ts’
ac tua l hea l th s ta tes . Th is can bes t be inves t iga ted by ana lys ing the re la t ionsh ips be tween the i tems and some more concre te ind ica tors o f ac tua l hea l th . There are sev- era l s tud ies wh ich re fer to these re lat ionsh ips [6-17 ] and wh ich , toge ther , cons t i tute a remarkab le ev idence bas is for judg ing the va l id i ty o f the EQ-5D-3L i tems . For a deeper unders tand ing , however , i t is a lso in teres t ing to know how the i tems re la te to soc io-demograph ic var i- ab les such as age , gender and educa t ion . As far as these soc io-demograph ic var iab les are re la ted to ac tua l hea l th , the re la t ionsh ips o f these var iab les w i th the EQ-5D-3L i tems a lso prov ide in forma t ion abou t the i tems ’va l id i ty . There are severa l s tud ies in wh ich these re la t ionsh ips have been invest iga ted [6 ,11 ,14 ,15 ,17-20 ] and the f ind- ings from these s tud ies enr ich the emp ir ica l know ledge re levan t for judg ing the va l id i ty o f the EQ-5D-3L i tems .
However , most o f the s tud ies jus t ment ioned have been per formed in on ly one spec i f ic coun try us ing on ly one spec i f ic language vers ion o f the EQ-5D-3L . There are on ly four stud ies in wh ich d i f ferent language ver- s ions have been app l ied . Three o f these have been per- formed us ing d i f ferent language vers ions w i th in the same country [12 ,15 ,18] and on ly one study re ferred to data from d i f ferent countr ies [19] . Ana lyses wh ich are re levant for invest igat ing va l id i ty and wh ich have been per formed separate ly for e i ther the d i f ferent language vers ions or the d i f ferent countr ies respect ive ly have been reported for on ly two o f the four stud ies [12 ,19] . Hence , there is not much emp ir ica l ev idence concern ing the extent to wh ich resu lts re ferr ing to the EQ-5D-3L items can be genera l ised across d i f ferent language ver- s ions and/or across d i f ferent countr ies . In fact , the re- su l ts o f one o f the few re levant stud ies [12] even suggest that th is is not the case . Ob ta in ing more in format ion
about the genera l izab i l i ty o f f ind ings concern ing the EQ-5D-3L items wou ld requ ire more stud ies in wh ich d i f ferent language vers ions o f the EQ-5D-3L are app l ied in d i f ferent countr ies .
A s tudy w i th the fea tures jus t ment ioned is presen ted here , per formed on pa t ients w i th type 2 d iabetes . Type 2 d iabe tes is a chron ic insu f f ic iency in the process ing o f g lucose in the b lood caused by too l i t t le insu l in be ing produced by the body or by the ava i lab le insu l in work ing ine f fec t ive ly . In the long run d iabe tes can lead to severe comp l ica t ions ; par t icu lar ly s troke , hear t a t tack , k idney fa i lure , u lcers o f the lower ex trem i t ies and impa irmen t o f s igh t [21 ,22 ] .
Pa t ien ts from Eng land , F in land , Germany , Greece , the Ne ther lands and Spa in were inves t iga ted and the corre- spond ing EQ-5D-3L language vers ions were used . The da ta from th is s tudy are ana lysed w i th regard to two ob jec t ives :
1 ) to inves t iga te the genera l izab i l i ty o f f ind ings concern ing the EQ-5D-3L i tems across the s tudy coun tr ies , and
2 ) to inves t iga te the va l id i ty o f the EQ-5D-3L i tems on the bas is o f the da ta from those coun tr ies for wh ich the f ind ings concern ing the EQ-5D-3L i tems are subs tant ia l ly the same .
Methods
Study part ic ipants and study conduct ion
The ana lyses were per formed us ing da ta from surveys o f type 2 d iabe tes pa t ien ts in Eng land , F in land , Germany , Greece , the Ne ther lands and Spa in wh ich were conduc ted dur ing a ma jor European pro jec t concerned w i th hea l th prov ider ne tworks [23 ] . Inc lus ion cr i ter ia for par t ic ipan ts were 1 ) tha t they were be ing trea ted for type 2 d iabe tes by the hea l th prov iders inves t iga ted in the pro jec t and 2 ) tha t they were a t leas t 18 years o ld . The hea l th prov iders inves- t iga ted in the s tudy se lec ted the pa t ien ts to be approached for par t ic ipa t ion accord ing to cr i ter ia de f ined by the re- searchers . The pa t ien ts were then con tac ted e i ther by pos t or by be ing d irec t ly g iven the ques t ionna ire when v is i t ing the ir hea l th care prov ider . The pa t ien ts who par t ic ipa ted in the survey comp le ted the ir ques t ionna ires on the ir own w ithout personne l from the serv ice prov ider or a re- searcher bes ide them . Depend ing on what was the most feas ib le me thod for the prov ider the par t ic ipan ts re turned the ir comp le ted ques t ionna ires e i ther by ma i l d irec t ly to the loca l pro jec t s tudy cen tres , or to the care prov ider who then passed them on to the s tudy cen tres . A l l surveys had been approved by na t iona l e th ica l comm i t tees and took p lace be tween Oc tober 2011 and March 2012 . Quest ionna ire
The ques t ionna ire used for the surveys con ta ined i tems
address ing soc io-demograph ic fea tures , hea l th , hea l th-
re la ted behav iour and hea l th trea tmen t . Mos t o f these i tems were no t inc luded in the ana lyses presented here . The ques t ionna ire i tems inc luded were those concern ing age , gender , educa t iona l a t ta inmen t , and secondary com- p l ica t ions o f d iabetes , and a l l EQ-5D-3L i tems . There were a lso two ques t ions concern ing the par t ic ipan t’ s competence in mas ter ing the ques t ionna ire language . In the Eng l ish vers ion o f the ques t ionna ire the f irst ques- t ion was‘ Wha t is your f irs t language?’and the ca tegor ies
‘ Eng l ish’and‘ O ther , p lease spec i fy’were g iven as answer op t ions . The second ques t ion was‘ I f Eng l ish is no t your f irs t language , how we l l do you mas ter i t? ’w i th the answer op t ions‘ No t a t a l l’ ,‘ Poor ly’ ,‘ Modera te ly’ ,‘ We l l’and‘ Per- fec t ly ’ . In the o ther language vers ions the word‘ Eng l ish’
was rep laced w i th the word for the language in wh ich the ques t ionna ire was formu la ted . Bo th ques t ions were re le- van t in se lec t ing wh ich ques t ionna ires were to be inc luded for the ana lyses .
Educa t iona l a t ta inmen t was assessed by ask ing par t ic i- pan ts whether they had le f t schoo l a f ter the m in imum schoo l leav ing age o f the ir coun try . Those answer ing
‘ yes’were c lass i f ied as hav ing a lower leve l o f educa t iona l a t ta inmen t than those who answered‘ no’ . A f ter leng thy d iscuss ions w i th researchers from a l l s ix invest iga ted coun tr ies th is assessment turned ou t to f i t bes t to a l l the s ix correspond ing educa t ion sys tems wh ich are a l l d i- verse in many respec ts .
F ive secondary comp l ica t ions o f type 2 d iabe tes were cons idered in the ques t ionna ire : s troke , k idney fa i lure , hear t prob lems , prob lems concerned w i th the lower ex- trem i t ies and prob lems w i th eyes . Each comp l ica t ion was addressed by a s ing le ques t ion . S troke was assessed by ask ing i f they had ever had a s troke , and k idney fa i lure by ask ing i f they were dependen t on d ia lyses or had had a prev ious k idney transp lan t . The o ther three secondary comp l ica t ions were addressed by ques t ions each o f wh ich in turn had three answer op t ions . For hear t prob lems these were : no prob lems ; hav ing had a by-pass or su f fer ing from ang ina , but never hav ing had a heart attack ; and hav ing had a heart attack . For prob lems w i th lower ex- trem it ies the opt ions were : no prob lems w ith legs , feet and toes caused by d iabetes ; hav ing les ions in legs , feet or toes caused by d iabetes , but no amputat ion caused by d iabetes ; and amputat ion o f a toe , foot or leg due to prob lems caused by d iabetes . The three answer opt ions for eye prob lems were : no prob lems ; prob lems caused by d iabetes , but no b l indness ; and b l indness as a resu lt o f d iabetes .
Stat ist ica l ana lyses
Ques t ionna ires were exc luded from ana lyses i f the par- t ic ipant cou ld no t su f f ic ien t ly mas ter the ques t ionna ire language and/or i f there were too many m iss ing va lues for the var iab les under cons idera t ion . Su f f ic ien t mas ter ing o f
the ques t ionna ire language was de f ined as e i ther be ing a na t ive speaker or as mas ter ing the ques t ionna ire language a t leas t‘ we l l’ . Hav ing too many m iss ing va lues was de f ined as there be ing e i ther more than one m iss ing va lue for the three soc io-demograph ic ques t ions , or more than one m iss ing va lue for the f ive ques t ions concern ing the sec- ondary comp l ica t ions or more than one m iss ing va lue for the f ive EQ-5D-3L i tems . The la t ter cr i ter ion was a com- prom ise be tween the demands o f no t re ly ing on in forma- t ion tha t was too ques t ionab le and o f no t exc lud ing too many par t ic ipan ts . I f there was no more than one m iss ing va lue for each o f the three ques t ion ca tegor ies , th is cou ld s t i l l be a t tr ibu ted to casua l s l ips by the responden t . More m iss ing va lues than th is were taken as an ind ica tor o f fun- damen ta l insu f f ic ienc ies in the responden t 's answers .
To ob ta in a bas ic unders tand ing o f the da ta , the d is tr i- bu t ions o f the three soc io-demograph ic fea tures and the f ive secondary comp l ica t ions were ana lysed for each coun- try separa te ly , and for a l l coun tr ies toge ther . Age was trea ted bo th as a con t inuous var iab le and as a ca tegor ica l var iab le w i th the ca tegor ies’ 18-54’ ,’ 55-64’ ,’ 65-74’ ,and
‘ o lder than 74’ . These ca tegor ies were chosen because they were expec ted to cover qua l i ta t ive ly d i f feren t age ranges . Coun try d i f ferences w i th regard to age were tes ted by compu t ing a mu l t ivar ia te l inear regress ion w i th age as the dependen t var iab le and dummy coded coun tr ies as inde- penden t var iab les . Coun try d i f ferences w i th regard to the rema in ing soc io-demograph ic var iab les , s troke , and k id- ney fa i lure were tes ted us ing Pearson’ s ch i-square tes t . Coun try d i f ferences on the three ‘ three-ca tegor ica l ’sec- ondary comp l ica t ions (prob lems w i th hear t , lower ex trem- i t ies , or eye prob lems ) and the f ive EQ-5D-3L i tems were ana lysed us ing the Kruska l-Wa l l is test . Th is test is spe- c ia l ly des igned for compar ing va lues o f var iab les w i th an ord ina l sca le leve l . It was chosen because the three- categor ica l i tems for the secondary comp l icat ions as we l l as the EQ-5D-3L items possess on ly th is sca le leve l . B ivar iate re lat ionsh ips o f the soc io-demograph ic fea- tures and the secondary comp l icat ions w ith the EQ-5D- 3L items were a lso invest igated us ing Kruska l-Wa l l is tests . The rema in ing ana lyses d irect ly re fer to the two ob ject ives presented in the introduct ion .
Genera l izab i l i ty o f f ind ings concern ing the EQ -5D -3L i tems
As men t ioned above the va l id ity o f the EQ-5D-3L i tems
is usua l ly inves t iga ted by ana lys ing the re la t ionsh ips o f
these i tems w i th demograph ic fea tures and w i th more
ob jec t ive fea tures o f hea l th . There fore , the cross-na t iona l
genera l izab i l i ty o f f ind ings concern ing the EQ-5D-3L
i tems was inves t iga ted here w i th regard to exac t ly these
re la t ionsh ips . To s imp l i fy these ana lyses the f ive EQ-5D-
3L i tems and a l l three-ca tegor ica l i tems re ferr ing to
secondary comp l ica t ions were d icho tom ised w i th one ca t-
egory be ing‘ no prob lems a t a l l’and the o ther‘ any
prob lems’ . The secondary comp l ica t ions wh ich were mea- sured w i th three-ca tegor ica l i tems were prob lems w i th hear t , lower ex trem i t ies and eyes . The i tems re ferr ing to s troke and to k idney fa i lure were a lready b inary var iab les . As coun try spec i f ic d i f ferences regard ing the re la t ionsh ips be tween the EQ-5D-3L i tems and o ther var iab les can on ly be reasonab ly inves t iga ted when there are va lues for a l l leve ls o f the inves t iga ted var iab les in a l l coun tr ies those soc io-demograph ic fea tures and secondary comp l ica t ions were exc luded from the ana lyses wh ich d id no t mee t th is cr i ter ion . The inc luded var iab les w i l l be re ferred to as the
‘ tes t var iab les ’be low .
To test whe ther there are coun try-spec i f ic d i f ferences regard ing re la t ionsh ips be tween the EQ-5D-3L i tems and the tes t var iab les two log is t ic regress ion mode ls were compared for each comb ina t ion o f EQ-5D-3L i tem and test var iab le . Bo th mode ls con ta ined the respec t ive d ichotom ised EQ-5D-3L i tem as dependen t var iab le . The f irs t o f the two mode ls con ta ined the test var iab le and dummy coded coun try as independen t var iab le ; the second mode l conta ined add i t iona l ly terms for the in ter- ac t ion be tween coun tr ies and tes t var iab le . S ta t ist ica l ly s ign i f ican t be t ter f i t o f the second mode l was taken as ev idence for coun try spec i f ic d i f ferences regard ing the re la t ionsh ip . Th is was tes ted us ing a l ike l ihood ra t io tes t . To ge t a lso descr ipt ive measures for the improvemen t o f mode l f i t Nage lkerke’ s pseudo R-square was compu ted for each mode l . Nage lkerke ’ s pseudo R-square re f lec ts how a l l inc luded independen t var iab les toge ther exp la in the dependen t var iab le . Th is s ta t is t ic is zero when the independen t var iab les do no t exp la in the dependen t var i- ab le a t a l l . When , in con tras t , the independen t var iab les exp la in the dependen t var iab le comp le te ly th is s ta t is t ic is equa l to one [24 ] .
For those comb ina t ions o f EQ-5D-3L i tems and tes t var iab le for wh ich the in terac t ion terms led to a s ta t is t i- ca l ly s ign i f ican t improvemen t o f the mode l f i t further ana lyses were per formed . These ana lyses a imed to iden- t i fy that coun try for wh ich the inves t iga ted re la t ionsh ip d i f fered mos t from the o ther coun tr ies . For th is purpose , log is t ic regress ion mode ls w i th the d icho tom ised EQ- 5D-3L i tem as dependen t var iab le were compu ted for each coun try separa te ly . These coun try spec i f ic regress ion mode ls con ta ined on ly the tes t var iab le as independen t var iab le . Th is was a lways one dummy var iab le (excep t for age , wh ich was mode l led w i th three dummy var iab les ) . I t was de term ined how the coun try spec i f ic regress ion coe f- f ic ien ts for these dummy var iab les dev ia ted from the cor- respond ing regress ion coe f f ic ien ts in the mode ls wh ich were compu ted for a l l coun tr ies toge ther w i thou t us ing in terac t ion terms . These dev ia t ions d irec t ly re f lec t how much the re la t ionsh ip for the respec t ive coun try d i f fers from the common core o f a l l coun tr ies . When i t was ma in ly the same coun try wh ich dev ia ted mos t from the
common core when there were s ta t is t ica l ly s ign i f ican t in- terac t ions then a l l ana lyses jus t descr ibed were repea ted w i thou t the da ta from th is coun try .
Va l id i ty o f the EQ -5D -3L i tems
The va l id i ty o f the EQ-5D-3L i tems was inves t iga ted w i th the da ta from those countr ies for wh ich there were no essen t ia l in terac t ion e f fec ts . Th is was ach ieved through in terpre t ing the resu l ts from those regress ion mode ls wh ich were compu ted for a l l coun tr ies toge ther and where in terac t ion terms as independen t var iab les were exc luded . Resu lts and d iscuss ion
More than 6000 ques t ionna ires were d is tr ibu ted o f wh ich 1638 were re turned and 1341 me t the inc lus ion cr i ter ia (see Tab le 1 ) . The propor t ion o f exc luded ques t ionna ires was larges t in Eng land (39 .2% ) wh ich was due to the fac t tha t abou t 40% o f a l l responden ts in th is samp le were o f Bang ladesh i e thn ic i ty who , due to lower leve ls o f s ta ted pro f ic iency in the Eng l ish language , d id no t mee t the in- c lus ion cr i ter ia for th is ana lys is . A l toge ther , 21 .6% o f the d is tr ibu ted ques t ionna ires were f ina l ly inc luded in the ana lyses and these propor t ions vary from 8 .6% for Eng land to 55 .2% for Germany . As a consequence percen tages and means de term ined from these da ta m igh t dev ia te from those means and percen tages wh ich wou ld have been ob- ta ined for the to ta l samp le . However , re la t ionsh ips be- tween var iab les can ra ther be expec ted to be the same for responders and non-responders . Hence , the low response ra tes w i l l mos t probab ly no t cons t i tu te a too grea t danger for the va l id i ty o f the ana lyses concern ing the re la t ion- sh ips be tween the EQ-5D-3L i tems and the tes t var iab les .
The mean age o f a l l inc luded par t ic ipan ts was 65 .4
years . The ma jor i ty o f the par t ic ipan ts was ma le (56 .9% ) ,
had a h igher educa t ion a t ta inmen t (53 .6% ) , and no sec-
ondary comp l ica t ions (rang ing from 78 .3% for no hear t
comp l ica t ions to 99 .7% for no k idney fa i lure ) (see Tab le 2 ) .
For the three soc io-demograph ic var iab les coun try d i f fer-
ences were s ta t is t ica l ly s ign i f ican t excep t for gender . For
the f ive secondary comp l ica t ions coun try d i f ferences were
s ign i f ican t excep t for k idney fa i lure (see Tab le 2 ) . As there
were three coun tr ies in wh ich there were no par t ic ipan ts
w i th k idney fa i lure , th is var iab le cou ld no t be app l ied for
the ana lyses in tended here . For a l l four secondary comp l i-
ca t ions w i th s ta t is t ica l ly s ign i f ican t coun try d i f ferences ,
the bes t hea l th s ta tes were repor ted in the Ne ther lands .
Da ta were ava i lab le for a l l ca tegor ies o f the f ive EQ-5D-3L
i tems ; however on ly for‘ usua l ac t iv i t ies’ ,‘ pa in/d iscom for t’ ,
and‘ anx ie ty/depress ion’were there da ta for a l l ca tegor ies
in every coun try (see Tab le 2 ) . There were s ign i f ican t d i f-
ferences be tween the coun tr ies for a l l f ive i tems . The
Du tch par t ic ipan ts had the lowes t ra tes o f repor t ing prob-
lems for mob i l i ty (31 .3% ) , se l f-care (5 .2% ) , usua l ac t iv i t ies
(22 .7% ) and pa in and/or d iscom for t (43 .2% ) and the
F inn ish par t ic ipan ts had the lowes t ra te o f repor t ing prob- lems w i th depress ion and/or anx ie ty (11 .4% ) .
Genera l izab i l ity o f f ind ings concern ing EQ -5D -3L items No Span ish par t ic ipan t be tween 55 and 64 years o f age repor ted prob lems w i th se l f-care and a l l Span ish par t ic i- pan ts w i th a prev ious s troke repor ted prob lems w i th mo- b i l i ty , usua l ac t iv i t ies and pa in or d iscom for t (da ta no t shown ) . Hence , the regress ion mode ls w i th in terac t ion terms cou ld not be computed for these comb inat ions o f EQ-5D-3L i tems and test var iab les (see Tab le 3) . A l l other or ig ina l ly intended ana lyses , however , cou ld be per formed , i .e . the s ign i f icance o f interact ions cou ld be tested in 31 cases .
In on ly 3 o f the 31 cases in wh ich in terac t ions cou ld be tes ted , the in terac t ion terms ra ised the mode l f i t s ign i f i- can t ly w i th a s ign i f icance leve l o f 0 .05 (see Tab le 3 ) . These three ana lyses concerned the re la t ionsh ips o f the i tem
‘ mob i l i ty’w i th gender ( increase in Nage lkerke’ s Pseudo R
2: 0 .012 , p < 0 .05 ) , o f the i tem‘ se l f-care’w i th prob lems w i th eyes ( increase in Nage lkerke’ s Pseudo R
2: 0 .015 , p < 0 .05 ) , and o f the i tem‘ pa in/d iscom for t’w i th prob lems w i th hear t ( increase in Nage lkerke’ s Pseudo R
2: 0 .012 , p < 0 .05 ) . In a l l three o f these cases the regress ion coe f f ic ien t for Spa in dev ia ted mos t from the correspond ing coe f f ic ien t for the mode l compu ted for a l l coun tr ies w i thou t the in terac t ion terms as independen t var iab les . When 31 s ig- n i f icance tes ts w i th a s ign i f icance leve l o f 0 .05 are per- formed then the probab i l i ty tha t more than two tes ts y ie ld a s ign i f ican t resu l t by chance is 0 .201 . There fore , the three s ign i f ican t resu l ts cou ld very we l l be fa lse re jec t ions o f the zero-hypo thes is . O f course , w i th a larger samp le s ize more e f fec ts m igh t be de tec ted . However , in those three cases where s ta t is t ica l ly s ign i f ican t in terac t ion e f fec ts were found , the d i f ferences be tween the Nage lkerke ’ s Pseudo R
2are sma l l . Hence , e f fec ts de tec ted w i th a larger samp le s ize can a lso be expec ted to be qu i te sma l l . So , the resu l ts pre- sen ted here sugges t tha t the s ix inves t iga ted d i f feren t lan- guage vers ions re la te in approx ima te ly the same way to the tes t var iab les . However , the fac t tha t the regress ion
coe f f ic ien ts for Spa in dev ia te mos t in a l l three s ign i f ican t in terac t ions m igh t a lso ind ica te tha t e i ther the i tems o f the Span ish vers ion are d i f feren t ly unders tood by the re- sponden ts , or tha t they ac tua l ly re la te d i f feren t ly to the tes t var iab les .
To inves t igate the genera l izab i l i ty o f f ind ings across the f ive coun tr ies o ther than Spa in , the same ana lyses were repea ted w i thout the Span ish da ta . A l l 35 in ter- ac t ion e f fec ts cou ld be tes ted and on ly one o f these 35 tes ts , i .e . the in terac t ion be tween coun tr ies and educa- t iona l leve l w i th regard to the i tem‘ pa in/d iscom for t’ , y ie lded a s ta t is t ica l s ign i f ican t resu l t on the 0 .05 leve l (see Tab le 4 ) . When 35 s ta t is t ica l tes ts w i th a s ign i f i- cance leve l o f 0 .05 are per formed then the probab i l i ty tha t a t leas t one tes t y ie lds a s ign i f ican t resu l t by chance is 0 .834 . There fore , the one and on ly s ign i f ican t resu l t can very we l l be a fa lse re jec t ion o f the zero-hypo thes is . Cons ider ing the pa t terns o f Nage lkerke’ s pseudo R-square (see Tab le 4 ) no large e f fec ts can be expec ted to be de- tec ted w i th a larger samp le s ize . Consequen t ly , the resu l ts prov ide strong ev idence for the genera l izab i l ity o f the resu ltsacrossEng land ,F in land , Germany , Greeceand the Nether lands .
Va l id ity o f the EQ -5D -3L items
Re la t ion be tween EQ -5D -3L i tems and tes t var iab les The va l id i ty o f the EQ-5D-3L i tems was on ly inves t iga ted w i th the da ta o f those f ive coun tr ies for wh ich there was s trong ev idence o f genera l izab i l i ty . For these da ta the re- su l ts from the regress ion ana lyses per formed w i th the tes t var iab les and dummy coded coun tr ies bu t w i thou t in ter- ac t ion terms as independen t var iab les were inspec ted more thorough ly (see Tab le 5 ) . These resu l ts show tha t the f irs t four i tems o f the EQ-5D-3L , i .e .‘ mob i l i ty’ ,‘ se l f- care’ ,‘ usua l ac t iv i t ies’and‘ pa in/d iscom for t’ ,re la teinthe same way to the seven tes t var iab les . The tendency o f repor t ing prob lems increases in a s ta t is t ica l ly s ign i f ican t manner w i th age , fema le gender , prev ious s troke , hear t prob lems , prob lems w i th lower ex trem i t ies and prob lems w i th eyes . The tendency o f repor t ing prob lems a lso Tab le 1 Genera l informat ion about the samp le
Quest ionna ires
d istr ibuted Quest ionna ires
returned Su f f ic ient language
competence Su f f ic ient data
aPart ic ipants inc luded
Eng land 3343 475 313 436 289
F in land 436 183 183 177 177
Ge rmany 462 286 282 259 255
G reece 600 179 179 165 165
The Ne the r lands 779 400 387 364 354
Spa in 625 115 115 101 101
A l l coun t r ies 6245 1638 1459 1502 1341
a
Pa r t ic ipan ts who answe red a t leas t two o f the th ree soc io -demog raph ic quest ions , a t leas t fou r o f the f ive ques t ions conce rn ing seconda ry comp l ica t ions , and a t
leas t fou r o f the f ive EQ -5D -3L ques t ions .
Tab le 2 D istr ibut ions of the invest igated var iab les
aEng land F in land Germany Greece Nether - lands Spa in A l l countr ies Soc io -demog raph ic fea tu res
Age (p < 0 .001 )
bMean 63 .2 64 .2 66 .1 66 .4 65 .9 68 .5 65 .4
SD 12 .8 9 .5 11 .4 10 .7 10 .3 11 .6 11 .2
M in imum 28 34 21 30 38 30 21
Max imum 90 98 92 89 89 92 98
<55 69 (24 .0% ) 25 (14 .4% ) 38 (15 .0% ) 20 (12 .1% ) 45 (12 .8% ) 12 (11 .9% ) 209 (15 .7% ) 55 -64 77 (26 .8% ) 60 (34 .5% ) 62 (24 .4% ) 48 (29 .1% ) 111 (31 .6% ) 17 (16 .8% ) 375 (28 .2% ) 65 -74 83 (28 .9% ) 68 (39 .1% ) 93 (36 .6% ) 52 (31 .5% ) 118 (33 .6% ) 38 (37 .6% ) 452 (33 .9% )
>74 58 (20 .2% ) 21 (12 .1% ) 61 (24 .0% ) 45 (27 .3% ) 77 (21 .9% ) 34 (33 .7% ) 296 (22 .2% ) Gende r (no t s ign i f ican t )
cFema le 114 (40 .1% ) 66 (37 .9% ) 127 (50 .0% ) 71 (43 .0% ) 147 (42 .6% ) 45 (45 .0% ) 570 (43 .1% ) Ma le 170 (59 .9% ) 108 (62 .1% ) 127 (50 .0% ) 94 (57 .0% ) 198 (57 .4% ) 55 (55 .0% ) 752 (56 .9% ) Educa t ion (p < 0 .001 )
cLow 164 (62 .8% ) 70 (42 .9% ) 87 (35 .4% ) 116 (73 .4% ) 84 (24 .7% ) 64 (68 .1% ) 585 (46 .4% ) H igh 97 (37 .2% ) 93 (57 .1% ) 159 (64 .6% ) 42 (26 .6% ) 256 (75 .3% ) 30 (31 .9% ) 677 (53 .6% ) Seconda ry comp l ica t ions
S t roke (p < 0 .05 )
cNo 263 (91 .0% ) 168 (94 .9% ) 228 (89 .4% ) 152 (92 .1% ) 337 (95 .7% ) 95 (95 .0% ) 1243 (92 .9% ) Yes 26 (9 .0% ) 9 (5 .1% ) 27 (10 .6% ) 13 (7 .9% ) 15 (4 .3% ) 5 (5 .0% ) 95 (7 .1% ) Hea r t (p < 0 .01 )
dNo p rob lems 215 (76 .0% ) 127 (78 .4% ) 177 (76 .6% ) 109 (69 .0% ) 286 (84 .4% ) 82 (82 .8% ) 996 (78 .3% ) P rob lems , no a t tack 40 (14 .1% ) 20 (12 .3% ) 32 (13 .9% ) 28 (17 .7% ) 30 (8 .8% ) 8 (8 .1% ) 158 (12 .4% ) Hea r t a t tack 28 (9 .9% ) 15 (9 .3% ) 22 (9 .5% ) 21 (13 .3% ) 23 (6 .8% ) 9 (9 .1% ) 118 (9 .3% ) K idney (no t s ign i f ican t )
cNo k idney fa i lu re 276 (99 .6% ) 173 (100 .0% ) 243 (99 .2% ) 158 (99 .4% ) 348 (100 .0% ) 100 (100 .0% ) 1298 (99 .7% ) K idney fa i lu re 1 (0 .4% ) 0 (0 .0% ) 2 (0 .8% ) 1 (0 .6% ) 0 (0 .0% ) 0 (0 .0% ) 4 (0 .3% ) Lowe r ex t rem i t ies (p < 0 .001 )
dNo p rob lems 230 (81 .3% ) 149 (86 .1% ) 185 (73 .4% ) 144 (87 .8% ) 318 (93 .8% ) 83 (83 .8% ) 1109 (84 .7% ) Mode ra te p rob lems 43 (15 .2% ) 23 (13 .3% ) 63 (25 .0% ) 18 (11 .0% ) 21 (6 .2% ) 15 (15 .2% ) 183 (14 .0% ) Ampu ta t ions 10 (3 .5% ) 1 (0 .6% ) 4 (1 .6% ) 2 (1 .2% ) 0 (0 .0% ) 1 (1 .0% ) 18 (1 .4% ) Eyes (p < 0 .001 )
dNo p rob lems 209 (73 .6% ) 155 (89 .1% ) 202 (79 .5% ) 134 (81 .7% ) 315 (91 .0% ) 73 (73 .0% ) 1088 (82 .3% ) Mode ra te p rob lems 74 (26 .1% ) 19 (10 .9% ) 52 (20 .5% ) 29 (17 .7% ) 31 (9 .0% ) 26 (26 .0% ) 231 (17 .5% ) B l ind 1 (0 .4% ) 0 (0 .0% ) 0 (0 .0% ) 1 (0 .6% ) 0 (0 .0% ) 1 (1 .0% ) 3 (0 .2% ) EQ -5D -3L i tems
Mob i l i ty (p < 0 .001 )
dNo p rob lems 142 (49 .3% ) 104 (58 .8% ) 167 (65 .5% ) 84 (50 .9% ) 242 (68 .8% ) 58 (58 .0% ) 797 (59 .6% ) Some p rob lems 143 (49 .7% ) 73 (41 .2% ) 88 (34 .5% ) 81 (49 .1% ) 110 (31 .3% ) 41 (41 .0% ) 536 (40 .1% ) Con f ined to bed 3 (1 .0% ) 0 (0 .0% ) 0 (0 .0% ) 0 (0 .0% ) 0 (0 .0% ) 1 (1 .0% ) 4 (0 .3% ) Se l f -ca re (p < 0 .001 )
dNo p rob lems 212 (73 .4% ) 157 (88 .7% ) 223 (87 .5% ) 149 (90 .3% ) 330 (94 .8% ) 83 (83 .0% ) 1154 (86 .5% )
Some p rob lems 67 (23 .2% ) 20 (11 .3% ) 30 (11 .8% ) 13 (7 .9% ) 15 (4 .3% ) 15 (15 .0% ) 160 (12 .0% )
increases w i th lower educa t ion for a l l four i tems , bu t on ly for three o f those i tems in a s ta t is t ica l ly s ign i f ican t man- ner . The s ta t is t ica l tes t for the i tem‘ se l f-care’jus t m isses a s ign i f ican t resu l t ; bu t the regress ion coe f f ic ien t for th is i tem (b =−0 .35 ) dev ia tes more from zero than those for the i tems‘ mob i l i ty’(b =−0 .33 ) and‘ pa in/d iscom for t’
(b =−0 .33 ) and the con f idence in terva ls for a l l four i tems over lap large ly (see Tab le 5 ) . There are s t i l l fur ther com- mona l i t ies be tween the f irs t four i tems . For the three soc io-demograph ic var iab les the abso lu te va lue o f the coe f f ic ien t is a lways larges t for the h ighes t age ca tegory in compar ison w i th the lowes t age ca tegory and a lways low- es t for educa t ion . For the four inves t iga ted secondary comp l ica t ions th is va lue is a lways larges t for prob lems w i th lower ex trem i t ies .
However , the regress ion coe f f ic ien ts a lso ind ica te a s l igh t d i f ference be tween the f irs t three i tems , i .e .‘ mob i l- i ty ’ ,‘ se l f-care’and‘ usua l ac t iv i t ies’ , and the i tem‘ pa in/d is- com for t’ . The la t ter i tem seems to be less a f fec ted by age
(b for age > 74 : 0 .92 ) and by the four secondary comp l ica- t ions o f d iabe tes (b range : 0 .65 to 1 .56 ) than the o ther three i tems (see Tab le 5) . For‘ age’and for‘ prev ious stroke’th is tendency is even expressed in the con f idence interva ls , i .e . for the age category‘ >74’the con f idence interva l for‘ pa in/d iscom fort’(0 .53 ; 1 .31) does no t over- lap w ith the con f idence interva l for the item‘ mob i l ity’
(1 .40 ; 2 .25) , and for‘ prev ious stroke’the con f idence interva l for‘ pa in/d iscom fort’(0 .17 ; 1 .14) does no t over- lap w i th the con f idence in terva l for the i tem‘ usua l ac t iv- i t ies ’(1 .25 ; 2 .20 ) (see Tab le 5 ) . There is s t i l l a fur ther d i f ference between the f irst three EQ-5D-3L i tems and the item‘ pa in/d iscom fort’ . Whereas‘ prob lems w ith the heart’const i tute that secondary comp l icat ion wh ich has thesma l lest e f fect on the f irst three i tems (b range : 0 .86 to 0 .98) , it is‘ prev ious stroke’wh ich has the sma l lest e f fect (b = 0 .65) on the item‘ pa in/d iscom fort’ .
The i tem‘ anx ie ty/depress ion’d i f fers qu i te d is t inc t ly from the o ther four EQ-5D-3L i tems . In con tras t to the o ther Tab le 2 D istr ibut ions of the invest igated var iab les
a(Con t inued )
Unab le 10 (3 .5% ) 0 (0 .0% ) 2 (0 .8% ) 3 (1 .8% ) 3 (0 .9% ) 2 (2 .0% ) 20 (1 .5% ) Usua l ac t iv i t ies (p < 0 .001 )
dNo p rob lems 158 (54 .9% ) 129 (72 .9% ) 182 (71 .7% ) 110 (67 .1% ) 272 (77 .3% ) 71 (70 .3% ) 922 (69 .0% ) Some p rob lems 103 (35 .8% ) 45 (25 .4% ) 67 (26 .4% ) 47 (28 .7% ) 77 (21 .9% ) 25 (24 .8% ) 364 (27 .2% ) Unab le 27 (9 .4% ) 3 (1 .7% ) 5 (2 .0% ) 7 (4 .3% ) 3 (0 .9% ) 5 (5 .0% ) 50 (3 .7% ) Pa in/d iscom fo r t (p < 0 .001 )
dNo 120 (41 .5% ) 77 (44 .0% ) 76 (30 .0% ) 65 (39 .6% ) 200 (56 .8% ) 43 (42 .6% ) 581 (43 .6% ) Mode ra te 129 (44 .6% ) 93 (53 .1% ) 158 (62 .5% ) 92 (56 .1% ) 141 (40 .1% ) 48 (47 .5% ) 661 (49 .6% ) Ex t reme 40 (13 .8% ) 5 (2 .9% ) 19 (7 .5% ) 7 (4 .3% ) 11 (3 .1% ) 10 (9 .9% ) 92 (6 .9% ) Anx ie ty/dep ress ion (p < 0 .001 )
dNo t 156 (54 .9% ) 156 (88 .6% ) 175 (70 .3% ) 34 (20 .9% ) 302 (85 .6% ) 56 (56 .0% ) 879 (66 .3% ) Mode ra te ly 108 (38 .0% ) 17 (9 .7% ) 67 (26 .9% ) 97 (59 .5% ) 50 (14 .2% ) 40 (40 .0% ) 379 (28 .6% ) Ex t reme ly 20 (7 .0% ) 3 (1 .7% ) 7 (2 .8% ) 32 (19 .6% ) 1 (0 .3% ) 1 (0 .3% ) 67 (5 .1% )
a
Due to m iss ing va lues the numbe rs o f cases eva lua ted fo r each va r iab le a re mos t ly lower than the samp le s izes . Pe rcen tages re fe r to the‘ w i th in coun t ry’
d is t r ibut ions o f the va r iab les (co lumns ) .
b
Tes t fo r coun t ry d i f fe rences pe r fo rmed w i th mu l t ip le l inea r reg ress ion w i th‘ coun t ry’as dummy coded independen t va r iab le .
c
Tes t fo r coun t ry d i f fe rences pe r formed w i th Pea rson’ s ch i -squa re tes t .
d
Tes t fo r coun t ry d i f fe rences pe r fo rmed w i th K ruska l -Wa l l is tes t .
Tab le 3 Mode l f its for data from a l l s ix study countr ies
aMob i l ity Se l f -care Usua l act iv it ies Pa in/D iscom fort Anx iety/Depress ion Age 0 .13 ; 0 .15 0 .14 ; n .d .
b0 .10 ; 0 .12 0 .07 ; 0 .09 0 .26 ; 0 .27
Gende r 0 .07 ; 0 .08
*0 .10 ; 0 .11 0 .07 ; 0 .08 0 .09 ; 0 .10 0 .27 ; 0 .27 Educa t ion 0 .04 ; 0 .04 0 .10 ; 0 .10 0 .06 ; 0 .06 0 .05 ; 0 .06 0 .27 ; 0 .27 P rev ious s t roke 0 .07 ; n .d .
b0 .13 ; 0 .13 0 .11 ; n .d .
b0 .05 ; n .d .
b0 .27 ; 0 .27 P rob lems w i th hea r t 0 .08 ; 0 .09 0 .13 ; 0 .14 0 .09 ; 0 .09 0 .06 ; 0 .07
*0 .26 ; 0 .26 P rob lems w i th lowe r ex t rem i t ies 0 .16 ; 0 .17 0 .19 ; 0 .19 0 .14 ; 0 .14 0 .12 ; 0 .13 0 .29 ; 0 .29 P rob lems w i th eyes 0 .09 ; 0 .09 0 .15 ; 0 .16
*0 .08 ; 0 .09 0 .08 ; 0 .08 0 .27 ; 0 .28
a
F i rs t numbe r in each ce l l is Nage lkerke’ sR
2fo r the mode l w i thou t in te rac t ion te rms , the second numbe r is Nage lkerke ’ sR
2fo r the mode l w i th in te rac t ion te rms . As te r isks beh ind the second numbe r symbo l ise the resu l ts o f the tes t as to whe the r the second mode l exp la ins the dependen t va r iab le s ign i f ican t ly be t te r than the f i rs t .
*=‘ p < 0 .05’ .
b
n .d . means no t de term inab le .
i tems i t is v ir tua l ly unre la ted to age and educa t ion . More- over , the regress ion coe f f ic ien ts ind ica te tha t i t is less a f- fec ted by the secondary comp l ica t ions w i th on ly‘ prev ious s troke’be ing an excep t ion . For‘ prob lems w i th lower ex- trem i t ies ’and for‘ prob lems w i th eyes’th is tendency is a lso ev iden t in the con f idence in terva ls , i .e . for‘ prob lems w i th lower ex trem i t ies ’the con f idence in terva l for‘ anx ie ty/de- press ion’(0 .59 ; 1 .31 ) does no t over lap w i th the con f idence in terva l for‘ mob i l i ty’(1 .44 ; 2 .18 ) , and for‘ prob lems w i th eyes’the con f idence in terva l for‘ anx ie ty/depress ion’(0 .43 ;
1 .10 ) does no t over lap the con f idence in terva l for‘ usua l ac- t iv i t ies ’(1 .25 ; 2 .20 ) (see Tab le 5 ) .
Re la t ionsh ips to prev ious s tud ies
The f ind ing tha t the f irst three EQ-5D-3L i tems are mos t s im i lar to each o ther whereas the las t i tem , i .e .
‘ anx ie ty/depress ion’ , d i f fers mos t is very we l l in l ine w i th resu l ts from fac tor ana lyses per formed in o ther s tud ies [25-27 ] . The f ind ing that hea l th impa irmen ts as re f lec ted by more ob jec t ive ind ica tors have an adverse e f fec t on Tab le 4 Mode l f its w ithout Span ish data
aMob i l ity Se l f -care Usua l act iv it ies Pa in/D iscom fort Anx iety/Depress ion Age 0 .14 ; 0 .15 0 .14 ; 0 .16 0 .10 ; 0 .12 0 .07 ; 0 .09 0 .27 ; 0 .29
Gende r 0 .07 ; 0 .07 0 .11 ; 0 .11 0 .07 ; 0 .07 0 .08 ; 0 .09 0 .28 ; 0 .29 Educa t ion 0 .04 ; 0 .05 0 .10 ; 0 .11 0 .06 ; 0 .06 0 .06 ; 0 .07
*0 .28 ; 0 .29 P rev ious s t roke 0 .07 ; 0 .07 0 .13 ; 0 .14 0 .10 ; 0 .11 0 .06 ; 0 .06 0 .28 ; 0 .28 P rob lems w i th hea r t 0 .09 ; 0 .10 0 .13 ; 0 .15 0 .09 ; 0 .10 0 .07 ; 0 .08 0 .28 ; 0 .28 P rob lems w i th lowe r ex t rem i t ies 0 .15 ; 0 .16 0 .19 ; 0 .19 0 .14 ; 0 .15 0 .12 ; 0 .13 0 .30 ; 0 .30 P rob lems w i th eyes 0 .09 ; 0 .10 0 .17 ; 0 .18 0 .10 ; 0 .11 0 .09 ; 0 .09 0 .29 ; 0 .29
a
F i rs t numbe r in each ce l l is Nage lkerke’ sR
2fo r the mode l w i thou t in te rac t ion te rms , the second numbe r is Nage lkerke ’ sR
2fo r the mode l w i th in te rac t ion te rms . As te r isks beh ind the second numbe r symbo l ise the resu l ts o f the tes t as to whe the r the second mode l exp la ins the dependen t va r iab le s ign i f ican t ly be t te r than the f i rs t .
*=‘ p < 0 .05’ .
Tab le 5 Regress ion coeff ic ients for mode ls w ithout interact ion terms , Span ish data exc luded
aMob i l ity Se l f -care Usua l act iv it ies Pa in/D iscom fort Anx iety/Depress ion Age
<55 ( re fe rence )
55 -64 0 .45* 0 .19 0 .24 0 .34 0 .11
0 .05 ; 0 .85 −0 .42 ; 0 .80 −0 .18 ; 0 .65 −0 .02 ; 0 .69 −0 .31 ; 0 .52
65 -74 0 .72*** 0 .43 0 .32 0 .35 0 .03
0 .33 ; 1 .11 −0 .15 ; 1 .01 −0 .08 ; 0 .72 −0 .00 ; 0 .69 −0 .38 ; 0 .43
>74 1 .82*** 1 .38*** 1 .30*** 0 .92*** −0 .14
1 .40 ; 2 .25 0 .80 ; 1 .96 0 .88 ; 1 .73 0 .53 ; 1 .31 −0 .59 ; 0 .30
Ma le gende r −0 .61*** −0 .46** −0 .61*** −0 .68*** −0 .46**
−0 .85 ;−0 .38 −0 .80 ;−0 .11 −0 .86 ;−0 .36 −0 .91 ;−0 .44 −0 .73 ;−0 .18
H ighe r educa t ion −0 .33* −0 .35 −0 .36** −0 .33* −0 .03
−0 .59 ;−0 .08 −0 .73 ; 0 .03 −0 .63 ;−0 .09 −0 .59 ;−0 .08 −0 .33 ; 0 .27 P rev ious s t roke 1 .28*** 1 .41*** 1 .72*** 0 .65** 0 .87***
0 .81 ; 1 .75 0 .92 ; 1 .90 1 .25 ; 2 .20 0 .17 ; 1 .14 0 .40 ; 1 .35 P rob lems w i th hea r t 0 .98*** 0 .86*** 0 .89*** 0 .68*** 0 .45**
0 .69 ; 1 .27 0 .47 ; 1 .24 0 .60 ; 1 .18 0 .38 ; 0 .98 0 .13 ; 0 .77 P rob lems w i th lowe r ex t rem i t ies 1 .81*** 1 .67*** 1 .62*** 1 .56*** 0 .95***
1 .44 ; 2 .18 1 .27 ; 2 .06 1 .27 ; 1 .96 1 .14 ; 1 .99 0 .59 ; 1 .31 P rob lems w i th eyes 1 .17*** 1 .46*** 1 .72*** 0 .99*** 0 .76***
0 .85 ; 1 .49 1 .09 ; 1 .84 1 .25 ; 2 .20 0 .64 ; 1 .34 0 .43 ; 1 .10
a
F i rs t en t ry in the ce l l is the reg ress ion coe f f ic ien t , i .e . the loga r i thm o f the odds ra t io . The as te r isks beh ind th is en t ry ma rk the resu lts o f the s ign i f icance tes t fo r
dev ia t ion f rom ze ro , w i th * =‘ p < 0 .05’ , **= ’ p < 0 .01’ , ***= ’ p < 0 .001’ . The numbe rs in the second row o f each ce l l a re the bounda r ies o f the 95% - in te rva l o f
con f idence fo r the reg ress ion coe f f ic ien t .
a l l f ive i tems is , w i th a few excep t ions [6-8 ,12 ,13 ,16] , a lso in l ine w i th the f ind ings in ear l ier s tud ies [6-17] . As in the resu l ts presen ted here , o ther s tud ies show tha t age has an adverse e f fec t on the f irst four EQ-5D-3L i tems [6 ,11 ,14 ,17 ,19 ,20 ] . However , in contras t to the f ind ings presen ted here , age a lso had a s ta t is t ica l ly s ign i f ican t ad- verse e f fec t on the i tem‘ anx iety/depress ion’in mos t o f the s tud ies in wh ich th is re la t ion has prev ious ly been in- ves t iga ted [11 ,14 ,17 ,19 ,20 ] . In on ly one o f these s tud ies was no such e f fec t found [6 ] . As in the s tudy presen ted here , women reported more prob lems than men for a l l f ive i tems in mos t o f the prev ious s tud ies in wh ich th is re la t ionsh ip had been inves t iga ted [11 ,14 ,17 ,19 ,20 ] . There was on ly one excep t ion [15 ] . There is a lso r ich ev idence tha t , jus t as in the s tudy presen ted here , the tendency o f repor t ing prob lems for the f irs t four EQ-5D-3L i tems in- creases w i th lower educa t ion [11 ,14 ,15 ,17 ,19 ,20 ] . However , in con tras t to the s tudy presen ted here , prev ious s tud ies a lso show a s ta t is t ica l ly s ign i f ican t pos i t ive e f fec t o f educa- t ion on the i tem‘ anx ie ty/depress ion’[11 ,14 ,15 ,17 ] or a t leas t a non-s ign i f ican t tendency in th is d irec t ion [19 ,20 ] . In tegra t ive in terpre ta t ion o f the resu l ts re levan t for va l id i ty Cons idered from on ly a concep tua l perspec t ive the con- s truc ts addressed by the f ive EQ-5D-3L i tems are re la ted in a d i f ferent way to each o ther . The f irs t three i tems are a l l concerned w i th bod i ly func t ion wh ich to a large de- gree can be a f fec ted by the same impa irmen ts ; the fourth i tem , i .e .‘ pa in/d iscom for t’ , descr ibes some th ing wh ich is phys ica l bu t wh ich is no t necessar i ly re la ted to func- t iona l res tr ic t ions ; the f i f th i tem , i .e .‘ anx iety/depress ion’ , descr ibes some th ing wh ich is no t phys ica l and wh ich can be a f fec ted by qu i te d i f ferent fac tors o ther than phys ica l hea l th . These concep tua l re la t ions be tween the i tems are very we l l re f lec ted by the resu l ts found in the s tudy presen ted here as we l l as by the resu l ts o f the pre- v ious s tud ies concern ing the fac tor ia l s truc ture o f the i tems [25-27 ] . Hence , these resu l ts prov ide ev idence for the in terna l va l id ity o f the i tems .
Bo th the s tudy presen ted here and prev ious s tud ies show tha t more prob lems are repor ted for the f irs t four EQ-5D-3L i tems w i th increas ing age and lower educa t ion . As phys ica l hea l th is known to decrease w i th age and lower educa t ion [28-31 ] these f ind ings fur ther corrobora te these i tems ’va l id i ty . The re la t ionsh ips o f age and educa- t ion w i th the i tem‘ anx ie ty/depress ion’ , however , are more comp l ica ted .
For the re la t ionsh ip be tween age and the i tem‘ anx- ie ty/depress ion ’two antagon is t ic med ia t ing mechan isms can be assumed . One mechan ism is that phys ica l hea l th decreases w i th age and tha t , th is in turn , increases anx- ie ty and/or depress ion [32-34 ] . On the o ther hand , mos t peop le a t an o lder age rece ive a pens ion income from wh ich they can l ive and wh ich can a l lev ia te some reasons
for be ing anx ious and/or depress ive . Moreover , o lder age for some peop le is assoc ia ted w i th a t ime for reduced work respons ib i l i t ies and increased le isure t ime wh ich can a lso reduce anx ie ty and/or depress ion . When these two antagon ist ic mechan isms work together no un iversa l adverse e f fect o f age on the item‘ anx iety/depress ion’
can be expected . In the data presented here , both mech- an isms m ight have neutra l ised each other whereas in most stud ies in l iterature the f irst mechan ism m ight have been stronger .
For the re la t ionsh ip be tween educa t ion and the i tem
‘ anx ie ty/depress ion’two antagon is t ic med ia t ing mecha- n isms can a lso be pos tu la ted . One mechan ism is tha t h igher educa t ion is assoc ia ted w i th be t ter phys ica l hea l th [28-31 ] , and be t ter phys ica l hea l th , in turn , is assoc ia ted w i th less anx ie ty and depress ion [32-34 ] . The o ther mech- an ism is tha t h igher educa t ion is very o f ten assoc ia ted bo th w i th more be ing expec ted from these peop le in the ir work pos i t ions and w i th the ir own expec ta t ions from l i fe in genera l be ing h igher , wh ich bo th increases the r isk o f be- com ing anx ious and depress ive . Assum ing these two an- tagon is t ic mechan isms imp l ies tha t no un iversa l adverse e f fec t o f educa t ion on the i tem‘ anx ie ty/depress ion’can be expec ted . In the da ta presen ted here , bo th mechan isms m igh t have neu tra l ised each o ther whereas in mos t s tud ies in l i tera ture the f irs t mechan ism m igh t have been s tronger .
Bo th the s tudy presented here and prev ious s tud ies show tha t ma les repor t fewer hea l th prob lems than fe- ma les . The in terpre ta t ion o f these f ind ings , however , is a lso comp l ica ted . In fac t , some emp ir ica l s tud ies ind ica te tha t ma les are hea l th ier than fema les [35-38 ] . However , the c lass ica l ma le se l f-concep t expec ts ma les to be bo th phys ica l ly and emo t iona l ly s trong [39 ] , wh ich reduces the tendency to adm i t impa irmen ts even i f they ac tua l ly ex is t . So , as far as the gender e f fec t in the answers corresponds to ac tua l d i f ferences in hea l th th is e f fec t cons t i tu tes fur- ther ev idence for the va l id i ty o f the i tems . However , to the ex ten t to wh ich the gender e f fec t is s tronger than the d i f ferences in ac tua l hea l th , th is e f fec t is ev idence for a re- sponse b ias and there fore for a spec i f ic res tr ic t ion o f va l id- i ty . W i th the ana lyses presen ted here the re la t ive in f luence o f bo th fac tors canno t be de term ined and add i t iona l re- search wou ld be requ ired .
Conc lus ions
The i tems o f the Eng l ish , F inn ish , German , Greek , Du tch ,
and Span ish vers ions o f the EQ-5D-3L re la te in approx i-
ma te ly the same way to age , gender , educa t ion , prev ious
s troke , hear t prob lems , prob lems w i th lower ex trem i t ies
and prob lems w i th eyes . However , for 3 o f the 31 per-
formed tes ts s ta t is t ica l ly s ign i f ican t dev ia t ions from the
same pa t tern were de tec ted and a l l o f these were large ly a t-
tr ibu tab le to the Span ish da ta . These resu l ts can s t i l l be ex-
p la ined by s ta t is t ica l var ia t ion caused by chance . However ,
they m igh t a lso sugges t tha t some th ing is d i f feren t e i ther w i th the European Span ish language vers ion o f the EQ- 5D-3L or w i th the ac tua l re la t ionsh ips be tween the EQ- 5D-3L i tems and the tes t var iab les . Fur ther s tud ies are requ ired for dec id ing be tween bo th poss ib le exp lana t ions . A f ter exc lud ing the Span ish da ta , on ly one o f the 35 per- formed s ta t is t ica l tes ts o f dev ia t ion from the same pa t tern produced a s ta t is t ica l ly s ign i f ican t resu l t . Th is prov ides s trong emp ir ica l ev idence tha t the i tems o f the Eng l ish , the F inn ish , the German , the Greek , and the Du tch vers ion o f the EQ-5D-3L re la te in the same way to the tes t var iab les . The aggrega ted resu l ts for Eng l ish , F inn ish , German , Greek and Du tch da ta prov ide fur ther ev idence for the va l id i ty o f the EQ-5D-3L i tems .
Compet ing interests
The au tho rs dec la re tha t they have no compe t ing in te res ts . Authors’contr ibut ions
UK has coo rd ina ted the su rvey in a l l s tudy coun t r ies , o rgan ised the su rvey in Ge rmany , e labo ra ted the bas ic concep t ion o f the pape r , pe r fo rmed the s ta t is t ica l ana lyses and w r i t ten mos t pa r ts o f the pape r . SE , RF , PF , TM and EP have o rgan ised the su rvey in the i r coun t r ies , d iscussed the concep t ion o f the pape r , c r i t ica l ly rev iewed the pape r and g iven impo r tan t con t r ibu t ions to i ts re f inemen t . MFBJ has g iven essen t ia l suppo r t in e labo ra t ing the concep t ion o f the pape r , c r i t ica l ly rev iewed seve ra l ea r l ie r ve rs ions o f the pape r and g iven impo r tan t con t r ibu t ions to i ts re f inemen t . A l l au tho rs read and app roved the f ina l manusc r ip t .
Acknow ledgements
The resea rch lead ing to these resu l ts has rece ived fund ing f rom the Eu ropean Commun i ty 's Seven th F ramewo rk P rog ramme (FP7/2007 -2013 ) unde r g ran t ag reemen t n ° 241741 . The su rveys have been pe r fo rmed w i th the spec ia l ass is tance o f Tom Bowen , E le f the r ia Ka ramp l i , Te resa Meneu , Pau lus To rkk i , and An te ro Vanha la . The au tho rs wou ld l ike to exp ress the i r g ra t i tude to the pa r t ic ipa t ing hea l thca re se rv ice p rov ide r o rgan isa t ions fo r the i r co -ope ra t ion and suppo r t in enab l ing the s tudy to take p lace . Author deta i ls
1
T r imbe rg Resea rch Academy , Un ive rs i ty o f Bambe rg , Bambe rg D -96045 , Ge rmany .
2Ins t i tu te o f Hea l th Po l icy & Managemen t , E rasmus Un ive rs i ty Ro t te rdam , PO Box 1738 , Ro t te rdam , DR 3000 , The Ne the r lands .
3Jo in t Resea rch Un i t in B iomed ica l Eng inee r ing , I IS La Fe - Un ive rs i ta t Po l i tècn ica de Va lènc ia , Bu leva r su r s/n , 46026 Va lenc ia , Spa in .
4The Ba lance o f Ca re G roup , 39a C leve land Road , London N1 3ES , UK .
5Depa r tmen t o f Indus t r ia l Eng inee r ing and Managemen t , Aa l to Un ive rs i ty , PO Box 15500 , Espoo , Aa l to 00076 , F in land .
6Depa r tmen t o f Hea l th Econom ics , Na t iona l Schoo l o f Pub l ic Hea l th , 196 A lexand ras Ave , 115 21 A thens , G reece .
7Depa r tmen t o f Psych ia t ry , Sec t ion Med ica l Psycho logy & Psycho the rapy , E rasmus MC , PO Box 2040 , CA 3000 Ro t te rdam , The Ne the r lands .
Rece ived : 20 June 2014 Accepted : 26 Novembe r 2014
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