Minimum skills required by children to complete healthrelated quality of life instruments for asthma: comparison of measurement properties

Transcription

1 Eur Respir J 1997; 10: DOI: / Prited i UK - all rights reserved Copyright ERS Jourals Ltd 1997 Europea Respiratory Joural ISSN Miimum skills required by childre to complete healthrelated quality of life istrumets for asthma: compariso of measuremet properties E.F. Juiper*, G.H. Guyatt* +, D.H. Feey*, L.E. Griffith*, P.J. Ferrie* Miimum skills required by childre to complete health-related quality of life istrumets for asthma: compariso of measuremet properties. E.F. Juiper, G.H. Guyatt, D.H. Feey, L.E. Griffith, P.J. Ferrie. ERS Jourals Ltd ABSTRACT: To gai a complete picture of a child's health-status, measuremet of health-related quality of life (HRQL) is ecessary. Sice parets do ot accurately perceive childre's HRQL, iformatio must be obtaied from the childre themselves. The aim of this study was to determie the miimum age ad readig skills required by childre to complete competetly the Paediatric Asthma Quality of Life Questioaire (PAQLQ), the Health Utilities Idex (HUI), the Feelig Thermometer ad the Stadard Gamble, ad to evaluate the validity of each for measurig HRQL i childre with asthma. Fifty two childre (age 7 17 yrs) with symptomatic asthma participated i a 9 week sigle cohort study with HRQL ad cliical asthma cotrol assessed every 4 weeks. childre provided very reliable data for the PAQLQ ad the HUI but they eeded grade 6 readig skills to complete the Stadard Gamble ad grade 2 skills for the Feelig Thermometer. I those childre who were able to provide reliable data, the PAQLQ had the best discrimiative ad evaluative measuremet properties, followed closely by the Feelig Thermometer. Measuremet properties i the Stadard Gamble were weaker ad although the HUI was very reliable it was ot actually measurig asthma-specific HRQL. The Paediatric Asthma Quality of Life Questioaire may be used with cofidece i cliical studies ad practice to provide a profile of childre's day-to-day experieces. I those childre with adequate skills to complete the test reliably, the Feelig Thermometer provides a good estimate of the value that childre place o their asthma health status. Eur Respir J 1997; 10: Depts of *Cliical Epidemiology ad Biostatistics, ad + Medicie, ad Cetre for Health Ecoomics ad Policy Aalysis, McMaster Uiversity, Hamilto, Otario, Caada Correspodece: E.F. Juiper Dept of Cliical Epidemiology ad Biostatistics McMaster Uiversity Faculty of Health Scieces 1200 Mai Street West Hamilto Otario Caada LN 3Z5. Keywords: Asthma paediatrics quality of life Received: April 1996 Accepted after revisio July Supported through a grat from Fisos Caada May paediatricias ow recogize the importace of icorporatig a assessmet of health-related quality of life (HRQL) ito their cliical studies. Covetioal cliical measures usually provide valuable iformatio about the status of the affected orga system but they rarely capture the fuctioal impairmets (physical, emotioal ad social) that are importat to the patiets i their everyday lives. If oe is to obtai a complete picture of a child's health status, oe has to measure both the covetioal cliical idices ad the child's HRQL. Parets do ot accurately perceive their childre's HRQL [1]. Therefore, we are depedet o obtaiig the iformatio directly from the child. Differet types of HRQL istrumets require differet levels of uderstadig, readig skills ad reasoig, but to date there is miimal iformatio to help ivestigators ad cliicias decide whether the childre they ited to study ca provide meaigful data from the istrumets they would like to use. Both geeric [2, 3] ad disease-specific paediatric HRQL questioaires [4, 5] are available for use i childre with asthma ad, i the future, with the growig importace of health ecoomics, we will see a icreased use of preferece measures ad utilities. Therefore, we felt that it was timely to determie the age ad skills required by childre for reliable completio of these differet types of istrumets. We selected four HRQL istrumets to represet the spectrum of istrumets likely to be used i the future. They represet the differet types of istrumets (geeric ad disease-specific questioaires ad utilities) ad each requires very differet types ad levels of skills: 1) the Paediatric Asthma Quality of Life Questioaire (PAQLQ) [4] is a iterviewer-admiistered disease-specific questioaire with resposes give, usig a sevepoit scale; 2) the Health Utilities Idex (HUI) Mark 2 ad Mark 3 system [2, 3] is a self-admiistered geeric questioaire which has predomiatly dichotomous resposes; 3) the Feelig Thermometer [6] is a coceptually simple preferece-measuremet istrumet; 4) the Stadard Gamble [6] is a utility istrumet that requires quite sophisticated coceptual skills. Our objectives i coductig this study were etirely practical. We wated to kow whether these published HRQL istrumets are capable of measurig

2 226 E.F. JUNIPER ET AL. HRQL i childre with asthma ad, if so, what are the miimum skills required for reliable completio. It was ot our itet to explore the theories of developmetal uderstadig i childre. These are certaily importat (e.g. childre's perceptio of death for the Feelig Thermometer ad the Stadard Gamble) but such a discussio would of ecessity be legthy ad detract from our practical objective. I additio, there are umerous excellet ad comprehesive discussios o these issues to be foud i the child developmet literature. I this study, we first estimated the miimum age, school grade ad readig skills eeded to complete each of these istrumets reliably ad the, i childre who were able to provide reliable data, we have examied the validity of these istrumets for measurig asthmaspecific quality of life i childre. Patiets Methods Usig otices placed i the local media ad paediatric asthma cliics, ad through parets who had take part i our adult asthma studies, we recruited 52 childre (aged 7 17 yrs) with asthma, as defied by the America Thoracic Society guidelies. Patiets experiecig asthma symptoms durig the week prior to erollmet with a score of less tha 6.5 o the symptom domai of the PAQLQ (7.0 = o impairmet ad 1.0 = severe impairmet) were icluded. We excluded childre if they: had illesses other tha asthma that affected quality of life; had recurret chest ifectio requirig treatmet with atibiotics; were uable to perform reliable peak expiratory flow rates at home; or had required oral steroids durig the previous 2 weeks. Each child was accompaied to the cliic o each visit by the primary caregiver, usually a paret. Childre over the age of 12 yrs ad all caregivers siged a iformed coset that had bee approved by the McMaster Uiversity Faculty of Health Scieces Ethics Committee. Study desig Childre were see i the cliic at erollmet ad after 1, 5 ad 9 weeks. At weeks 1, 5 ad 9, a traied iterviewer admiistered the PAQLQ, the HUI, the Feelig Thermometer ad the Stadard Gamble. istrumets were admiistered with the caregiver abset. Questios i the PAQLQ ad the HUI were ever iterpreted, paraphrased or explaied for the childre. If a child appeared to have difficulty with a questio, it was repeated verbatim. At each visit, we measured spirometry before ad after a brochodilator. At the first visit, we tested childre for their word recogitio ad readig comprehesio skills usig the Brigace Comprehesive Ivetory of Basic Skills [7]. At weeks 5 ad 9, the childre completed a global ratig of chage questioaire that asked whether there had bee ay chage i their asthma sice the previous visit. For 1 week before each follow-up visit, the childre completed a daily symptom ad medicatio diary ad made morig peak flow measuremets. At the cliic visit, a cliical asthma cotrol score was calculated [4]; this is a composite of asthma symptoms (awoke by symptoms at ight, wakig i the morig with symptoms, sputum, limitatio of daily activities), spirometry (forced expiratory volume i oe secod (FEV1) <70% of predicted value) ad brochodilator use (β-agoist use more tha four times per day). A poit is scored for each of the six items preset (0=good cotrol, 6=very poor cotrol). At weeks 1, 5 ad 9, the caregiver completed the Paediatric Asthma Caregiver's Quality of Life Questioaire [] ad the Impact-o-Family Scale [9]. At weeks 5 ad 9, caregivers completed a global ratig of chage questioaire [10] o their child's asthma symptoms. Quality of life istrumets Paediatric Asthma Quality of Life Questioaire [4]. This istrumet was developed to measure asthma-specific quality of life i childre aged 7 17 yrs. The 23 items i the questioaire cover those problems associated with asthma which have bee idetified by childre with asthma as beig importat ad bothersome to them i their day-to-day lives [11]. The words used i the questioaire are those that the childre themselves use to describe their problems. The items are i three domais: symptoms (=10); emotioal fuctio (=); ad activity limitatio (=5). Three of the activity items are "idividualized" ad idetified by the child at the first visit. The questioaire is available i both iterviewer ad self-admiistered formats. I this study, we used the iterviewer-admiistered versio. The respose optios of the PAQLQ are o a seve-poit scale where 1 idicates maximum impairmet ad 7 idicates o impairmet. Patiets are provided with a card o which the resposes are listed. A verbal descriptor follows each umber, e.g. 1=extremely bothered, 2=very bothered, 3=quite bothered... 7=ot bothered. The iterviewer reads the questio ad the child gives the respose, from the card, that best describes his or her experieces durig the previous week. The questioaire takes approximately mi to complete at the first visit ad 7 mi at follow-up. Prior to use i Eglish ad all subsequet laguages, the questioaire was pretested i childre to esure that eve the yougest uderstood each of the questios ad the respose optios. For overall quality of life ad for each of the domais, the Miimal Importat Differece (MID) has bee determied to be a chage i score of 0.5 [4]. The MID has bee defied as "the smallest differece i score i the domai of iterest which patiets perceive as beeficial ad would madate, i the abseces of troublesome sideeffects or excessive cost, a chage i the patiet's maagemet" [10]. Health Utilities Idex [2, 3]. This is a geeric multiattribute questioaire used to assess health status i the HUI2 ad HUI3 systems [2, 3]. There are 10 attributes (visio, hearig, speech, mobility, dexterity, self-care, feeligs, memory, thikig ad pai ad discomfort). The impairmet experieced i the first five attributes is ascertaied usig Guttma-style questios. For istace,

3 MEASURING ASTHMA HRQL IN CHILDREN 227 i the visio attribute, the first questio asks "Are you usually able to see well eough to read ordiary ewsprit without glasses or cotact leses?". If the respose is "yes", the respodet goes o to the ext attribute. If the respose is "o", the patiet cotiues to the questios which progressively ascertai the level of visio impairmet. For the fial five attributes, respose optios rage from three-poit to five-poit. The time frame is ot specified. To calculate the overall score for each patiet, we used the weightigs that had bee derived previously from a multiplicative, multi-attribute utility fuctio based o the prefereces of a radom sample of the geeral populatio [3, 4]. I this study, if childre had isufficiet readig skills to uderstad the questios or istructios, the iterviewer admiistered the questioaire. The questioaire takes approximately 5 7 mi to complete. The Feelig Thermometer [6]. This preferece-measuremet istrumet explores how patiets feel about their ow health state ad the value they place upo it. The istrumet looks like a thermometer with clearly defied ed poits: 0 = least preferred health state (death), ad 100 = most preferred health state (perfect health). I this study, patiets first read aloud (if ecessary with the iterviewer's help) a descriptio of three hypothetical "marker" health states, derived from the PAQLQ: Mild asthma: "You have asthma but it hardly bothers you at all. Occasioally, you wheeze ad are a little short of breath. Your asthma does ot limit you i ay sports or games. You have o problems at school. Your asthma does ot bother you at ight. Your asthma is ever frighteig." Moderate asthma: "You have asthma ad it bothers you quite a bit. You wheeze quite ofte ad get short of breath. Your asthma limits you i may thigs you like doig, such as sports ad games. Your asthma sometimes wakes you up at ight. You get frustrated by your asthma ad sometimes a attack is a bit frighteig." Severe asthma: "You have asthma ad it is really bothersome. You feel wheezy ad it is difficult to breath a lot of the time. You ca't joi i ay sports or games. At ight it is difficult to sleep because of your asthma. Quite ofte you get bad asthma attacks ad these are very frighteig." We asked the childre to place a marker o the thermometer to reflect their feeligs about each of the three health states. We the asked the patiets to thik about how their ow asthma had bee durig the previous week ad to place a marker o the thermometer to reflect their feeligs about this. Oly this fial score was used i the aalysis. The istrumet takes approximately 12 mi to complete at the first visit ad 7 mi at followup. The Stadard Gamble [6]. This utility istrumet also measures the value that patiets place o their ow health state. A full descriptio of the protocol for elicitig values may be foud elsewhere [6]. Coceptually, patiets are asked to thik about a health state ad the to cosider whether they would prefer to remai i that health state or take a chace with a ew (imagiary) treatmet. They are told that the ew treatmet has the ability to retur them to perfect health immediately with o sideeffects but may cause istat death. I other words, patiets are asked whether they would prefer the certaity of remaiig i their curret health state or whether they would prefer to take a gamble with the treatmet which will result i either perfect health or death. Iitially, if they take the treatmet (gamble), the probability of perfect health is set at 100% with absolutely o chace of death. those who uderstad the cocept choose to take the ew treatmet (the gamble) rather tha stay i their preset health state. I theory, the probability of perfect health is the gradually reduced (ad the chace of death icreased) util the patiet decides to remai i his/her ow curret health state rather tha take the ew treatmet (the gamble). I practice, the probability of perfect health (p) ad death (1-p) is varied util a poit of idifferece is foud. The idifferece probability represets the value that the patiet places o his/her health state. I this study, we first admiistered the Stadard Gamble with each of the three hypothetical asthma states used for the Feelig Thermometer ad the we asked childre about their ow asthma durig the previous week. Oly the score for the child's ow health state was used i the aalysis. The istrumet takes approximately 30 mi to admiister at the first visit ad 20 mi at follow-up. Before admiisterig the Stadard Gamble to a child, we explaied the etire procedure to the paret. Noe declied to have it admiistered to their childre. Word recogitio ad readig comprehesio We used the Brigace Comprehesive Ivetory of Basic Skills [7] to obtai each child's Word Recogitio Placemet ad Readig Vocabulary Comprehesio Placemet. For the former, the child is asked to read aloud lists of words which progressively become more difficult. A child must correctly proouce five of 10 words i a category to pass to the ext level. I the comprehesio test, the child is show three groups of five words. I each group, oe word does ot belog. The child is asked to idetify the three icorrect words (oe from each group) ad must get two right to pass o to the ext ad more difficult level. The Brigace testig system origiated i the USA ad the results of the tests are based o the USA school gradig system. Other questioaires used i the study Paediatric Asthma Caregiver's Quality of Life Questioaire []. This self-admiistered questioaire assesses the quality of life of parets of childre with asthma. It has four items o activity limitatios ad ie o emotioal fuctio. The questioaire presets resposes to each item o a seve-poit scale ad caregivers recall impairmets experieced durig the previous week. The istrumet has good reliability, resposiveess ad validity []. Impact-o-Family Scale [9]. This 24 item quality of life istrumet evaluates the impact of a child's illess o

4 22 E.F. JUNIPER ET AL. family fuctio. It has four domais: fiacial (=4); family/social (=9); persoal strai (=6); ad mastery (=5), with resposes to each item preseted o a fourpoit Likert scale (strogly agree to strogly disagree). Iteral cosistecy (Crobach's alpha) for overall impact ad for each domai rages Global ratig of chage questioaires [10]. These questioaires ask about chages i health status ad quality of life sice the previous cliic visit. At each follow-up visit, we asked both childre ad caregivers whether there had bee ay chage i the child's asthma sice their previous cliic visit, scorig resposes o a 15- poit scale from -7 (a very great deal worse) to 0 (o chage) to +7 (a very great deal better). Classifyig patiets as chaged or uchaged Each patiet had two study periods (2 5 weeks ad 6 9 weeks). For each period, we categorized patiets either as havig stayed the same (Group A) or chaged (Group B) usig three idepedet methods: 1) if patiets scored -1, 0 or + 1 o the symptom global ratig of chage questioaire, they were cosidered to have stayed the same ad if they scored betwee -7 ad -2 or betwee +2 ad +7 they were cosidered to have chaged; 2) if the caregiver scored -1, 0 or +1 o their perceptio of whether the child's symptoms had chaged, the child was cosidered stable, for all other scores the child was cosidered to have chaged; 3) usig oly cliical data (asthma cotrol score, steroid ad beta-agoist use, peak flow rates, spirometry ad cliical commets i the patiet's chart) ad blided to the HRQL data, oe of the ivestigators (EFJ), at the time of each cliic visit, classified patiets as uchaged or chaged. Agreemet betwee the methods was examied usig a weighted kappa statistic. Testig competece We reasoed that if childre fully uderstood the istrumets, those with stable asthma (Group A) would provide data that was cosistet (good reproducibility/ reliability) ad resposes would be accurate (good crosssectioal validity). For the estimate of reproducibility, if a child cotributed more tha oe pair of observatios to Group A, our statisticia (LEG) used a radom umber geerator directly o the database to select oe of the two pairs of observatios for the estimate. First, we calculated the relatioship betwee the betwee-subject ad the total variace to obtai a itra-class correlatio coefficiet (ICC). If reliability appeared poor (low ICC), we plotted the withi-subject stadard deviatio agaist age, school grade ad readig ad comprehesio grade to estimate the miimum level of each that would yield reproducible data. Regressio aalysis was used to determie whether the estimates of reliability above ad below chose cut-poits were sigificatly differet. Sice these were post hoc aalyses, we have lowered the covetioal level of statistical sigificace to p<0.01. For the method of determiig cross-sectioal validity, see Validity below. Testig the measuremet properties For discrimiative use (cross-sectioal surveys), istrumets eed to have good reliability ad cross-sectioal costruct validity, ad for evaluative use (cliical trials), istrumets eed to have good resposiveess ad logitudial costruct validity [12]. Reliability ad resposiveess. We estimated reliability, as described above, by calculatig a ICC usig data from childre whose asthma remaied stable betwee cosecutive visits (Group A). We estimated resposiveess i three ways. First, we assessed the ability of the istrumets to detect withi-subject chage i patiets who chaged (Group B) usig paired t-tests. Secod, we examied the ability of the istrumets to distiguish betwee Groups A ad B i terms of chage i HRQL over a 4 week period usig upaired t-tests. For both estimatios, symmetry of the data from those who improved ad those who deteriorated justified our chagig the sig i those who deteriorated. Third, we calculated the resposiveess idex ( / SD) [13]. Differeces i the resposiveess idex betwee istrumets were tested usig paired t-tests. Some patiets experieced a chage i their quality of life durig both study periods ad therefore cotributed two observatios to Group B. To esure that this did ot result i a overestimate of the precisio of resposiveess, we iflated the variace to take ito accout withi-subject correlatios by the quatity 1+(-1)ρ where ρ is the ICC of the chage scores ad =2 (the umber of observatios per subject). Validity. I addressig validity, we could have asked either whether the istrumets were valid for measurig asthma-specific HRQL or whether they were valid for measurig HRQL i geeral. We chose the former ad thus asked childre completig the Feelig Thermometer ad the Stadard Gamble to tell us about impairmets specifically related to their asthma. Before aalysig the data, four ivestigators (EFJ, GHG, DHF, LEG) together made predictios about the degree of correlatio we should expect to fid betwee the four istrumets beig tested ad other idices of cliical asthma severity ad quality of life if ideed the four istrumets were measurig asthma-specific HRQL (a priori predictios). We evaluated the cross-sectioal costruct validity of the four istrumets usig oly data from the first cliic visit. We calculated the correlatios betwee each of the four istrumets ad the other idices of cliical asthma severity ad HRQL. We the examied how closely these actual correlatios matched our a priori predictios. Logitudial costruct validity was evaluated i a similar maer except that the correlatios were betwee chages i scores betwee cosecutive visits. Results 52 patiets fiished the study ad provided complete data sets. Their demographic data ad baselie HRQL scores are show i table 1. Patiets represeted

5 MEASURING ASTHMA HRQL IN CHILDREN 229 Table 1. Patiet characteristics ad health-related quality of life at erollmet Patiet characteristics Patiets 52 Geder F/M 22/30 Age yrs 12.0±3.1 (7 17) FEV1 % pred 5±16.6 Medicatios Noe 2 Brochodilators aloe 15 Ihaled steroids ad brochodilators 31 Cromoglycate aloe 4 History of atopy* 44 Health-related quality of life at erollmet Paediatric Asthma Quality of Life Overall 5.19±0.95 ( ) Symptoms 5.09±1.0 ( ) Activities 4.56±1.16 ( ) Emotios 5.72±0.90 ( ) Health Utilities Idex 0.9±0.09 ( ) Feelig Thermometer 66.3±14. (30 9) Stadard Gamble (=40) 0.2±0.15 ( ) Values are mea±sd with rage i parethesis, apart from patiet umber, geder, medicatios ad history of atopy which are give i absolute umbers of patiets. *: exacerbatio of asthma symptoms o exposure to specific allerges. FEV1: forced expiratory volume i oe secod; % pred: percetage of predicted value. a wide rage of urba/rural ad socioecoomic backgrouds. The majority were Caucasia. Whe categorizig whether patiets stay the same (Group A) or chage (Group B) durig each time iterval, we usually use the patiets' ow global ratig of chage [14]. Although the overall kappa (κ=0.71) suggested that the childre perceived the chage i their health status well, i the yougest age group this perceptio was poor (7 10 yrs: κ=0.35). We have show subsequetly that parets have a very poor perceptio of chage i their child's asthma status [1] ad, therefore, it would have bee iappropriate to use the paret's global ratigs. Good cocordace betwee the older (11 17 yrs) childre's global ratig ad the cliical ratig (κ=0.77) suggested that the optimal ad most cosistet approach would be to use the cliical ratig. Uderstadig of the istrumets ad reliability of completio Paediatric Asthma Quality of Life Questioaire. The childre had little difficulty uderstadig the questios, the respose optios or their task i aswerig the questios. The wordig of each item was ot expected to be a cocer sice childre with asthma had chose them ad the coceptual uderstadig of each questio had bee carefully evaluated durig the pretest [4]. However, we were particularly iterested i whether the childre would experiece ay difficulty uderstadig the cocept of the seve-poit scale. Every child gave all resposes uaided ad good reliability ad validity data (see below) provided additioal cofidece that eve the yougest uderstood ad used the respose optios well. Noe of the childre had difficulty selectig appropriate activities for the idividualized sectio of the questioaire. The oly otable problem with the PAQLQ was the time specificatio i youger childre. Some of these childre had difficulty with the cocept of "durig the last week". We dealt with this problem by idetifyig a evet that had occurred a week ago ad framig the questios i relatio to this evet. Thirty seve patiets cotributed 57 sets of observatios to the "stayed the same" category (Group A). Whe oe radomly selected observatio per patiet cotributed to the estimatio of reliability, the withi-subject stadard deviatio was 0.17 with a ICC of 0.95 (table 2). This was cosistet through each of the domais (ICC: ) [4], ad for each age group (7 10 yrs: ICC=0.9; yrs: ICC=0.96; yrs: ICC=0.7). These results provided strog evidece that all childre aged 7 17 yrs ca complete the PAQLQ cosistetly. Good cross-sectioal validity provided evidece of accuracy i these patiets (table 3). Therefore, it appears that all childre aged 7 17 yrs ca complete the questioaire with competece. Health Utilities Idex. Most childre completed this self-admiistered questioaire uassisted. The youger oes ad those with limited readig skills required help which was adjusted accordig to the idividual child's eeds. I those with iadequate readig skills, the iterviewer read aloud all the questios ad the respose optios. I older childre, she read aloud oly those words that the child could ot read. I the 37 patiets i Group A, the withi-subject stadard deviatio was 0.02 ad the ICC of 0.93, strogly suggestig that over the age of 7 yrs, all childre ca complete the questioaire cosistetly. Cross-sectioal validity was poor (table 3) ad therefore it is impossible to determie from these data whether the cosistecy was accompaied by accuracy. Feelig Thermometer. Whe we icluded all 37 childre i the aalysis, the withi-subject stadard deviatio was ad the ICC was The low ICC Table 2. Reliability of scores i patiets with stable asthma (Group A) Istrumet Subjects Withi- Betwee- ICC subject subject SD SD PAQLQ Overall Symptoms Activities Emotios HUI Feelig Thermometer patiets Age yrs School Word Recogitio Comprehesio Stadard Gamble patiets Age 12 yrs School Word Recogitio Comprehesio ICC: itraclass correlatio coefficiet; PAQLQ: Paediatric Asthma Quality of Life Questioaire; HUI: Health Utilities Idex.

6 20 E.F. JUNIPER ET AL. Table 3. Cross-sectioal costruct validity + Cliical asthma Quality of life Asthma FEV1 Peak flow β-agoist PAQLQ PAQLQ Impact-o- Patiets cotrol % pred rates use Overall Overall family Istrumet (Pre-bd) A priori predictio <0.20 < > PAQLQ - Overall NA HUI Feelig Thermometer patiets Age yrs School Word Recogitio Comprehesio Stadard Gamble Age 12 yrs School Word Recogitio Comprehesio : Pearso correlatio coefficiet. NA: ot applicable. For further defiitios, see tables 1 ad 2. suggested that some childre may have experieced difficulty uderstadig the istrumet or their task. Figure 1 shows that there was a decrease i the withi-subject stadard deviatio i childre aged yrs or older, those i school grade 3 or higher ad those with at least grade 2 word recogitio ad comprehesio skills. Usig all these cut-poits teded to result i improved reliability (table 4). Good cross-sectioal validity i the older ad more skilled childre provides evidece of accurate resposes (table 3). Stadard Gamble. Oly childre i Group A were able to complete the Stadard Gamble ad provide a score. Whe all were icluded i the aalysis, the withisubject stadard deviatio was 0.15 ad the ICC was Figure 2 shows that the withi-subject stadard Withi-subject stadard deviatio a) Years c) Age Word recogitio grade b) d) School grade Comprehesio grade Fig. 1. Feelig thermometer: improvemet i reproducibility (withi-subject stadard deviatio) with icreasig: a) age; b) comprehesio; c) word recogitio; ad d) school grade i patiets with stable asthma. : umber of subjects i each group.

7 MEASURING ASTHMA HRQL IN CHILDREN 21 Table 4. Differeces i reliability above ad below cut poits Predictor ICCs below ad Ability of the (Cut poit) above cut-poit predictor to detect differeces i Below Above reproducibility p* Feelig Thermometer Age (< vs yrs) (=4) (=33) Word recogitio (<2 vs 2) (=3) (=34) Comprehesio (<2 vs 2) (=3) (=34) School grade (<3 vs 3) (=4) (=33) Stadard Gamble Age (<12 vs 12 yrs) (=11) (=1) Word recogitio (<6 vs 6) (=10) 19 Comprehesio (<6 vs 6) (=13) (=16) School grade (<6 vs 6) (=11) (=1) *: p<0.01 idicates that the predictor was able to differetiate betwee reliability above ad below the cut poit (see text). ICC: itraclass correlatio coefficiet. deviatio dropped at age 12 yrs, above school grade 6 ad above grade 6 readig ad comprehesio skills. Usig these cut-off poits resulted i improved reliability (table 4) ad, i these childre, there was moderately acceptable cross-sectioal validity. Compariso of measuremet properties The measuremet properties of the four istrumets have bee determied usig oly reliable data. For the PAQLQ ad the HUI, all 52 childre were icluded i the aalysis. For the Feelig Thermometer ad the Stadard Gamble we used oly childre above the cutoff poits show i table 4. Discrimiative properties. The reliability of each istrumet has bee described i detail i the sectio above. For cross-sectioal costruct validity, correlatios betwee each istrumet ad both cliical asthma measures ad other estimates of HRQL are show i table 3. The PAQLQ ad the Feelig Thermometer provided correlatios that were moderately close to predicted. For the Stadard Gamble, readig skills grade 6 provided correlatios that were still acceptably close to predicted, whereas age 12 yrs ad school grade 6 did ot. For the HUI, the correlatios were ot close to predicted for the cliical asthma measures but moderately close to predicted for the HRQL measures. a) 0.2 b) Withi-subject stadard deviatio c) 0.05 Years Age 17 3 d) Comprehesio grade Word recogitio grade School grade Fig. 2. Stadard Gamble: improvemet i reproducibility (withi-subject stadard deviatio) with icreasig: a) age; ad b) comprehesio; c) word recogitio; ad d) school grade i patiets with stable asthma. : umber of subjects i each group.

8 22 E.F. JUNIPER ET AL. Evaluative properties. For the estimatio of resposiveess, 32 patiets cotributed 47 sets of observatios to the chaged category (Group B), 27 improvemets ad 20 deterioratios. The PAQLQ ad the Feelig Thermometer both showed good resposiveess (table 5). Table 5. Resposiveess: the ability of the istrumet to detect chage Istrumet Group A Group B Differeces (patiets (patiets i (A vs B) with stable whom asthma p-value + asthma) chaged) PAQLQ Overall 0.01± ±0. < (=57) (=47) Symptoms 0.03± ±0.2 < (=57) (=47) Activities -0.03± ±1.32 < (=57) (=47) Emotios 0.01± ±1.09 < (=57) (=47) HUI 0.01± ± (=57) (=45) Feelig Thermometer patiets -12±13.5* 11.5±1.7* (=57) (=47) Age yrs -0.76± ±15.3 < (=50) (=42) School grade ± ±15.1 < (=50) (=42) Word recogitio 2-0.5± ±15.3 < (=52) (=46) Comprehesio 2-0.5± ±15.3 < (=52) (=46) Stadard Gamble patiets -0.03± ± (=45) (=34) Age 12 yrs ± ±0.15* 0.04 (=25) (=23) School ± ±0.15* 0.0 (=19) (=21) Word recogitio ± ±0.12* 0.1 (=19) (=21) Comprehesio ± ± (=11) (=13) *: p<0.05; : p<0.0001, withi-subject chage (paired t-test). + : upaired t-test. For further defiitios, see table 2. Both istrumets were able to detect chages i the patiets whose health status chaged (Group B) ad to differetiate these patiets from those who remaied stable (Group A). I childre at grade 6 or higher, the Stadard Gamble was able to detect improvemets i Group B but was uable to differetiate betwee Groups A ad B. The HUI was uresposive. For each istrumet, we calculated the resposiveess idex ( /SD ) (table 6). The PAQLQ has the highest resposiveess ad was sigificatly more resposive tha the HUI. Other differeces did ot reach sigificace. For logitudial validity, the PAQLQ correlatios were closest to predicted with the Feelig Thermometer ad the Stadard Gamble ot quite so close (table 7). For the HUI, correlatios were cosistetly low. Comprehesio Discussio Our results suggest that childre as youg as 7 yrs have little difficulty completig the PAQLQ ad the high reliability scores i stable patiets ad good crosssectioal validity leaves little doubt that the childre were both cosistet ad accurate i their uderstadig of the questios ad the respose optios. I this study, the iterviewer-admiistered versio was used. Studies curretly uderway are examiig the readig skills required for the self-admiistered versio. Although reliability for the HUI was excellet, cross-sectioal validity was poor i all age groups ad, therefore, it is impossible to determie, from this study, whether the cosistecy of resposes was accompaied by accuracy of uderstadig. However, other validatio studies suggest that childre do uderstad the questios ad tasks accurately [2, 3]. For the Feelig Thermometer, oly the yougest childre experieced difficulty ad our results for both reliability ad validity suggest that there are o problems of comprehesio for childre with at least grade 2 readig skills. The Stadard Gamble is coceptually more difficult ad we foud that childre eeded to have a least grade 6 readig skills before oe could have cofidece i their resposes. Table 6. Compariso of resposiveess betwee istrumets Istrumet Patiets HUI Feelig Feelig Stadard Stadard Thermometer- Thermometer- Gamble- Gamble- subjects Comprehesio 2 subjects Comprehesio 6 (0.14) (0.4) (0.67) (0.22) (0.51) PAQLQ (0.91) 47 *** * NS ** NS HUI (0.14) 45 NS * NS NS Feelig Thermometer- 47 NS NS NS subjects (0.4) Feelig Thermometer- 46 * NS Comprehesio 2 (0.67) Stadard Gamble- 34 NS subjects (0.22) Stadard Gamble- 25 Comprehesio 6 (0.51) The resposiveess idex is show i paretheses after the title of each istrumet. 1. Resposiveess idex = / SD. *: p<0.05; **: p<0.01; ***: p< NS: osigificat. For further defiitios see leged to table 2.

9 MEASURING ASTHMA HRQL IN CHILDREN 23 Table 7. Logitudial costruct validity + Cliical asthma Quality of life Global ratigs Asthma FEV1 % Peak β-agoist PAQLQ PACQLQ Impact o Child's Caregiver cotrol pred flow use Overall Overall family symptoms re child's Istrumet score (Pre-bd) rates symptoms A priori predictio < > PAQLQ - Overall N/A HUI Feelig Thermometer patiets Age yrs Word recogitio Comprehesio Stadard Gamble Age 12 yrs Word recogitio Comprehesio Values are Pearso correlatio coefficiets. N/A: ot applicable. For defiitios, see tables 1, 2 ad 3. For practical purposes, it would be desirable to use a child's age to decide his/her ability to complete a HRQL test. However, as show i tables 2 ad 3, stadardized readig tests provide substatially better guidace. I this study, we also looked at school grade. This is certaily better tha age but grades i this study come from the Otario school system where childre begi grade 1 i the caledar year of their sixth birthday ad occasioally repeat grades o the basis of poor attaimet. Therefore, the results may ot be applicable outside the provice or coutry. Istrumet measuremet properties As we have described i detail i a previous publicatio [4], the PAQLQ has strog discrimiative ad evaluative properties. The other three istrumets varied i their success. Whe, i the subsequet discussio, we refer to the Feelig Thermometer ad the Stadard Gamble, we are restrictig ourselves to the subpopulatios i which istrumet reliability was high. The HUI was highly reliable but completely uresposive ad ot valid as either a discrimiative or evaluative istrumet for asthma-specific HRQL. The high reliability tells us that the istrumet is measurig somethig ad data from other studies suggest that it is measurig HRQL [2, 3]. I this study, we excluded childre with other illesses but the high ICC may have stemmed from such impairmets as the eed to wear glasses. As with ay relatively short geeric istrumet, there is the risk that the questios will ot capture the impairmets associated with a specific medical coditio [15]. I this case, the HUI does ot measure paediatric asthma-specific quality of life ad ivestigators should ot try to use it for this purpose. The Feelig Thermometer worked well as both a discrimiative ad evaluative istrumet; it had very good reliability, resposiveess ad validity. The Stadard Gamble worked less well but still had acceptable measuremet properties. Whe reflectig o the success of the Feelig Thermometer ad the Stadard Gamble, the reader should remember the way i which the istrumets were admiistered. Patiets were asked to rate three scearios presetig mild, moderate ad severe asthma ad the to thik specifically about their asthma whe ratig their ow HRQL. Had they bee admiistered usig more geeric health state scearios ad the childre asked to focus o their health i geeral, the results might have bee quite differet. This implies that the HUI, a failure at measurig asthma-specific HRQL, may have bee doig a better job of measurig overall HRQL. We did ot admiister other geeral HRQL measures that would have allowed us to explore this hypothesis. A limitatio of this study is the relatively small ad possibly homogeeous sample. Although we edeavoured to erol patiets to represet a wide rage of socioecoomic backgrouds ad from both rural ad urba settigs, most of the childre ad their parets were Caucasia. I additio, all the childre were i the Otario school system where readig ad umeracy skills may be give differet emphasis ad itroduced at differet times compared to other provices ad coutries. Testig of these istrumets i other settigs will icrease our cofidece i the geeral applicability of the results. I coclusio, this study has show that the Paediatric Asthma Quality of Life Questioaire is quick, easy to uderstad, ad valid for both discrimiative (survey) ad evaluative (cliical trial/practice) use. It provides iformatio o the differet aspects of health-related quality of life that are troublesome to childre with asthma (symptoms, emotios ad activity limitatios) ad, very importatly, it is possible to place a cliical iterpretatio o the data [4]. The Feelig Thermometer is a good algorithm for evaluatig the value that childre with asthma place o their health status. It is quick to complete ad, i childre with grade 2 readig skills, it has very good measuremet properties. By providig oly a sigle umber, cliical uderstadig of patiet's experieces is limited, but a sigle umber o a stadardized scale (0=death, 1=perfect health) is ofte a desirable feature for health ecoomists ad those resposible for the allocatio of healthcare resources. Ulike the Feelig Thermometer, the Stadard Gamble meets the assumptios of utility theory ad the results ca be

10 24 E.F. JUNIPER ET AL. used i cost/utility aalyses. However, it is complex, log ad difficult to admiister, ca oly be used i childre with grade 6 readig skills ad has oly very modest measuremet properties. The Health Utilities Idex is quick, easy ad reliable, but ot valid for measurig asthma-specific quality of life i childre. This suggests that the Paediatric Asthma Quality of Life Questioaire ca be used cofidetly i cliical trials ad cliical practice to provide a profile of a child's experieces, but for specialized studies, such as health care utilizatio ad other pharmacoecoomic studies, the Feelig Thermometer may be more appropriate. The Stadard Gamble ad Health Utilities Idex are ulikely to be of use i childre with asthma. Ackowledgemets: The authors thak P. Rosebaum for his perceptive commets ad suggestios durig the preparatio of the mauscript, A. Willa for statistical support ad M. Guldemod ad T. Va Bevere for their help ad guidace i evaluatig readig skills. Refereces 1. Guyatt GH, Juiper EF, Feey DH, Griffith LE. Childre ad adult perceptios of childhood asthma. Pediatrics 1997; 99: Feey DH, Furlog W, Boyle M, Torrace GW. Multiattribute health status classificatio systems: health utilities idex. Pharmacoecoomics 1995; 7: Torrace GW, Furlog W, Feey DH, Boyle M. Multiattribute preferece fuctios: health utilities idex. Pharmacoecoomics 1995; 6: Juiper EF, Guyatt GH, Feey DH, Ferrie PJ, Griffith LE, Towsed M. Measurig quality of life i childre with asthma. Qual Life Res 1996; 5: Frech DJ, Christie MJ, Sowde AJ. The reproducibility of the childhood asthma questioaires: measures of quality of life for childre with asthma 4 16 years. Qual Life Res 1994; 3: Torrace GW. Measuremet of health state utilities for ecoomic appraisal: a review. J Health Eco 196; 5: Brigace AH. Brigace comprehesive ivetory of basic skills. Curriculum Associates Ic., North Billerica, Massachusetts Juiper EF, Guyatt GH, Feey DH, Ferrie PJ, Griffith LE, Towsed M. Measurig quality of life i the parets of childre with asthma. Qual Life Res 1996; 5: Stei REK, Riessma CK. The developmet of a impacto-family scale: prelimiary fidigs. Med Care 190; 1: Juiper EF, Guyatt GH, Willa A, Griffith LE. Determiig a miimal importat chage i a disease-specific quality of life istrumet. J Cli Epidemiol 1994; 47: Towsed M, Feey DH, Guyatt GH, Furlog WJ, Seip AE, Dolovich J. Evaluatio of the burde of illess for pediatric asthma patiets ad their parets. A ergy 1991; 67: Guyatt GH, Kirsher B, Jaeschke R. Measurig health status: What are the ecessary measuremet properties. J Cli Epidemiol 1992; 45: Guyatt GH, Walter S, Norma G. Measurig chage over time: assessig the usefuless of evaluative istrumets. J Chro Dis 197; 40: Juiper EF, Guyatt GH, Ferrie PJ, Griffith LE. Measurig quality of life i asthma. Am Rev Respir Dis 1993; 147: Rutte-va Molke MPMH, Clusters F, et al. Compariso of performace of four istrumets i evaluatig the effects of salmeterol o asthma quality of life. Eur Respir J 1995; : 9.