Brief communication
Is the standard SF-12Health Survey valid and equivalent for a Chinese population?
Cindy L.K.Lam1,Eileen Y.Y.Tse1&Barbara Gandek2
1Family Medicine Unit,the University of Hong Kong,Hong Kong SAR(E-mail:clklam@hku.hk);2IQOLA Project,Health Assessment Lab,Boston,MA USA
Accepted in revised form15June2004
Abstract
Introduction:Chinese is the world’s largest ethnic group but few health-related quality of life(HRQoL) measures have been tested on them.The aim of this study was to determine if the standard SF-12was valid and equivalent for a Chinese population.Methods:The SF-36data of2410Chinese adults randomly selected from the general population of Hong Kong(HK)were analysed.The Chinese(HK)specific SF-12 items and scoring algorithm were derived from the HK Chinese population data by multiple regressions. The SF-36PCS and MCS scores were used as criteria to assess the content and criterion validity of the SF-12.The standard and Chinese(HK)specific SF-12PCS and MCS scores were compar
ed for equivalence. Results:The standard SF-12explained82%and89%of the variance of the SF-36PCS and MCS scores, respectively,and the effect size differences between the standard SF-36and SF-12scores were less than0.3. Six of the Chinese(HK)specific SF-12items were different from those of the standard SF-12,but the effect size differences between the Chinese(HK)specific and standard SF-12scores were mostly less than0.3. Conclusions:The standard SF-12was valid and equivalent for the Chinese,which would enable more Chinese to be included in clinical trials that measure HRQoL.
Key words:Health-related quality of life,SF-12,Chinese,Validity,Equivalence
Introduction
Chinese make up nearly a quarter of the world’s population.They should be included in global and cross-cultural clinical trials but this is often not possible in studies that measure health-related quality of life(HRQoL)because of language and cultural barriers.Most HRQoL measures are in English and originate from the Western culture,so they need to be translated and validated before they can be applied to the Chinese.The Chinese (Hong Kong)translation of the MOS36-item Short Form Health Survey(SF-36)and its physical and mental health summary(PCS and MCS) Scales have been shown
to be valid and equivalent for the Chinese[1–5],but the length of the SF-36 limits its acceptability in some clinical trials that need to measure a number of outcomes.The standard SF-12Health Survey(SF-12),an abbre-viated form of the SF-36that yields the PCS and MCS scores,is becoming a popular HRQoL measure in clinical trials because it can be com-pleted in a few minutes[6,7].
The items and scoring algorithm of the standard SF-12were derived from data of a US general population survey in1990[6–8].The standard SF-12PCS and MCS scores are norm-based on the US general population whose mean is50and standard deviation(SD)is10[6,9].The12items include two from each of the physical functioning, role-physical,role-emotional and mental health scales and one item from each of the bodily pain, general health,vitality and social functioning scales of the SF-36.The items were selected by multiple regressions in order to explain the largest proportion of the total variance in the SF-36PCS
Qual Life Res(2005)14:539–547ÓSpringer2005
and MCS scores.The response to each item is weighted separately by the PCS and MCS regres-sion coefficient and then summated to give the standard SF-12PCS and MCS scores,respectively.
A small number and weighting of items may make a HRQoL measure more culture-sensitive [10,11].
All previous studies on the validity and equivalence of the standard SF-12were carried out in Caucasian populations[8,12].There was very little data from any Chinese or Asian population whose cultures are quite different from those of the West.The rank orders by item mean of three(PF9, GH3and RE3)SF-36items were found to be different between the HK Chinese and US popu-lations[1].Although the differential item func-tioning(DIF)of a few items did not affect the validity of the SF-36Scales that summated all the items without weighting[1,13],they may have an effect on the validity and equivalence of the much shorter standard SF-12.
The aim of this study was to determine if the standard SF-12was valid and equivalent for the Chinese population of Hong Kong,or whether a Chinese(HK)specific SF-12was needed.The standard SF-12is valid if it really measures the SF-36PCS and MCS scores,which are what it pur-ports to measure.The selected items should be representative and adequate in explaining the SF-36PCS and MCS scores(content validity),and the SF-12should give similar PCS and MCS scores as the SF-36(criterion validity).The standard SF-12 is equivalent if no more than three of the12items selected specifically from the Chinese(HK)popu-lation were different from those of the standard SF-12,as that found in other countries(item equivalence)[8];and if there is no important dif-ference between the results of the Chinese(HK) specific and standard scoring algorithms(mea-surement equivalence)[8,14,15].
Methods
Data of2410Chinese adults randomly selected from the general population of Hong Kong that were collected in the Chinese(Hong Kong)SF-36 norming survey in1998were used for analysis in this study.The detailed sampling and data collec-tion methods have been described in previous pa-pers[16,17].All subjects answered the Chinese (Hong Kong)translation of the SF-36and a structured questionnaire on sociodemographic data.Each subject was also asked to indicate whether he/she had ever been diagnosed by a doctor to have hypertension,diabetes mellitus, heart disease,stroke,chronic pulmonary disease, chronic joint disease,psychological illness or any other chronic disease.A subject was classified as not having any chronic disease if the responses to these chronic disease questions were all negative. Table1shows that the sociodemographic charac-teristics of the subjects were similar to those of the general adult population in Hong Kong[18].The sample was comparable to the US population sample[19]from which the standard SF-12was derived in mean age(42.9vs.43.6years)and sex distribution(47.8%vs.48%males).
The Chinese(HK)specific SF-12items were selected by multiple regressions of the Chinese (HK)specific SF-36PCS and MCS scores derived from the HK Chinese adult population[3],based on the criteria of the International Quality of Life Assessment(IQOLA)Project for cross-cultural adaptatio
n of the SF-12[8].The Chinese(HK) specific PCS and MCS regression constants and coefficients for each item response were obtained by regressing the Chinese(HK)specific SF-36PCS and MCS scores on the Chinese(HK)specific item scores.The SAS programme was used for the multiple regressions analyses.The SPSS Pro-gramme for Windows10.0(SPSS Inc.Chicago,IL, USA)was used for all other data analyses.
The standard SF-12PCS and MCS scores were calculated by the standard algorithm described in the SF-12Manual[6].The Chinese(HK)specific and standard mean SF-12PCS and MCS scores were determined for all subjects and by self-re-ported chronic disease groups.
Content validity was assessed by the proportion of total variance of the SF-36PCS and MCS scores explained by the SF-12PCS and MCS,and P90%was the expected standard[6,8].It was further assessed by Pearson correlations between the SF-12and SF-36PCS and MCS scores and the expected standard was P0.9[6,8].Effect size dif-ference between corresponding SF-12and SF-36 PCS and MCS scores was used to determine if the SF-12gave similar or different results from those of the SF-36(Criterion validity).Effect size dif-ference between the SF-36and SF-12scores was
540
calculated by dividing their difference by the standard deviation(SD)of the SF-36summary score.
Measurement equivalence between the standard and Chinese(HK)specific SF-12wasfirst assessed by Pearson correlations(expected standard P0.9) and then the effect size differences between the standard and Chinese(HK)specific scores.The effect size difference was calculated by dividing the difference between the corresponding SF-12 scores by the SD of the Chinese(HK)specific SF-12score.The standard and Chinese(HK)SF-12 scores were also compared by chronic disease groups in order to determine if they performed differently in different groups.A spectrum of chronic diseases(Heart,chronic pulmonary,psy-chological and chronic joint)that are known to affect HRQoL were used as tracer conditions[20]. There is no consensus on what the minimally important difference(MID)in HRQoL scores should be.Kazis et al.showed that the effect size changes in scores measured by the Arthritis Im-pact Measurement Scale were mostly between0.3 and0.5in the treatment group[21];and Wyrwich showed that the MID of the Chronic Heart Failure Questionnaire scores corresponded to effect size changes of0.34–0.37[22].We therefore adopted Cohen’s moderate effect size of0.3–0.5as the MID in this study[23,24].
Results
The Chinese(HK)specific SF-12PCS and MCS scales
First forward stepwise regressions of the Chinese (HK)specific SF-36PCS and MCS scores on the SF-36items selected two items each from the physical functioning(PF1,PF8)and mental health (MH3,MH4)scales,and one item each from the role-physical(RP3),bodily pain(BP1),social functioning(SF1)and role-emotional(RE3) scales.The second forward stepwise regressions, with the general health item(GH1)and the above items forced into the model,selected the remaining items(RP2,VT4and RE1)that explained the greatest variance of the HK Chinese specific SF-36 PCS and MCS scores.It is an IQOLA criterion that GH1should be included in all versions of SF-12because it is an item common to many HRQoL measures[8].Table2shows the Chinese(HK) specific SF-12items,in comparison with the standard SF-12items.The items that were differ-ent are shown in bold.The numbers in brackets correspond to the question numbers in the SF-36 Health Survey.
Table3shows the regression coefficients of the Chinese(HK)specific SF-12items and those of the
Table1.Sociodemographic characteristics of study sample compared with the Hong Kong general population
Sample
N=2410Hong Kong general adult population a N=5,333,610
Mean age(years)42.942.3
Age group(years)
18–4456.7%58.6%
45–6423.7%27.4%
65or above15.3%14.0%
Refused to answer  4.2%0%
Male47.8%48.3%
Female52.2%51.7%
Marital status
Now married58.0%59.4%
Never married33.8%31.9%
Widow/widower  5.8%  6.0%
Divorced/separated  1.3%  2.7%
Refused to answer  1.1%0%
Educational level
No schooling  6.9%8.4%
Primary22.3%20.5%
Secondary52.2%54.6%
Tertiary17.8%16.4%
Refused to answer0.9%0%
Social class by occupation
Managers and
administrators
N.A.10.7%b
Professional  3.1%  5.5%
Associate professional14.7%15.0%
Skilled worker35.4%33.5%c
Semi-skilled worker24.6%15.0%d
Non-skilled worker14.4%19.8%e
Refused to answer7.7%0%
a Data from the Hong Kong2001Population Census.
b This occupation category is not applicable to the social class
by occupation classification.
c Craft workers,plant an
d machin
e operators and assemblers.
d Servic
e and shop sales workers.
e Workers in elementary occupation,agriculture andfishery,
and unclassified.
541
standard SF-12items,derived from the HK gen-eral Chinese population sample.The regression coefficient of the best response choice of each item is not shown because it is the indicator variable. The Chinese(HK)specific PCS and MCS regres-sion coefficients of each item response were used separately to weight each item response for the calculation of the PCS and MCS scores.The weight f
or the best response choice of each item is zero.Summation of the relevant Chinese(HK) specific regression constant and item response PCS and MCS regression coefficients would give the Chinese(HK)specific SF-12PCS and MCS scores, respectively.
Content and criterion validity of the SF-12PCS and MCS
The R2in Table3indicates the proportion of total variance in the SF-36PCS or MCS score that was explained by the corresponding SF-12summary score.The standard SF-12PCS and MCS ex-plained82%and89%of the total variances of the standard SF-36PCS and MCS,respectively.The Chinese(HK)specific SF-12PCS and MCS ex-plained88%and90%of the total variances of the Chinese(HK)specific SF-36PCS and MCS, respectively.
Table4shows the correlations between the SF-12and SF-36PCS and MCS scores.The correla-tions between the corresponding SF-36and SF-12 summary scores all reached the expected standard of0.9.
The mean and standard deviation(SD)of the Chinese(HK)specific and standard SF12and SF-36PCS and MCS scores of the whole sample and by self-reported chronic disease groups are shown in Table5.The effect size differences(effect size1) between corresponding SF-36and SF-12scores were
all less than0.3.
Measurement equivalence between the chinese (HK)specific and standard SF-12
As shown in Table4,the correlations between the corresponding standard and Chinese(HK)specific SF-12PCS and MCS scores were just short of0.9. The standard and Chinese(HK)specific SF-12 scores are compared in Table5.The mean stan-dard SF-12PCS and MCS for the overall HK Chinese population were50.2and48.4,respec-tively,which were similar to the US general pop-ulation means of50.The Chinese(HK)specific and standard SF-12detected similar significant differences between each chronic disease group and the‘no chronic disease’group.The largest difference between the Chinese(HK)specific and standard SF-12scoring algorithms was the PCS score of people reporting heart diseases,with an effect size of0.36.
Discussion
The standard SF-12did not satisfy the criterion on item equivalence for the Chinese population in
Table2.The Chinese(HK)specific SF-12items compared with the standard SF-12items
SF-36scales Chinese(HK)specific SF-12items Standard SF-12items
Physical functioning(PF)PF1(3a)Vigorous activities PF2(3b)Moderate activities
PF8(3h)Walking several blocks PF4(3d)Climbing severalflights Role-physical(RP)RP2(4b)Accomplished less RP2(4b)Accomplished less
RP3(4c)Limited in kind of work RP3(4c)Limited in kind of work
Bodily pain(BP)BP1(7)How much bodily pain
have you had BP2(8)how much did pain interfered with work
General health(GH)GH1(1)Your GH1(1)Your
Vitality(VT)VT4(9i)Did you feel tired VT2(9e)Did you have a lot of energy
Social functioning(SF)SF1(6)Extent social activities
was interfered SF2(10)How much time social activities was interfered
Role-emotional(RE)RE1(5a)Cut down time on work RE2(5b)Accomplish less
RE3(5c)Didn’t do work as carefully RE3(5c)Didn’t do work as carefully Mental health(MH)MH3(9d)Felt calm&peaceful MH3(9d)Felt calm&peaceful
MH4(9f)Felt downhearted&blue MH4(9f)Felt downhearted&blue 542
543
Table3.Forward stepwise regressions of SF-36PCS and MCS scores on the SF-12item responses
Item_Response scores PCS regression coefficients MCS regression coefficients
Chinese(HK)specific Standard Chinese(HK)specific Standard
PF1_1)8.042639–  2.795780–
PF1_2)3.641426–  1.121187–
PF2_1–)6.609693–  3.461042
PF2_2–)2.782074–  1.314947
PF4_1–)6.269240–  2.586866
PF4_2–)2.427698–0.752688
PF8_1)16.203705–7.818665–
PF8_2)7.963922–  3.164988–
RP2_1)4.343623)4.390177)0.705448  1.022170
RP3_1)5.044296)5.0474760.256528  1.278842
BP1_1)17.012005–  3.635025–
BP1_2.2)12.695771–  2.349628–
BP1_3.1)9.002881–  1.931547–
BP1_4.2)6.377284–  1.507313–
BP1_5.4)3.772960–0.652800–
BP2_1–)12.257268–  2.208989
BP2_2–)10.594807–  2.500285
BP2_3–)7.912197–  1.500170
BP2_4–)4.970550–  1.033358
GH1_1)8.704344)8.042873)0.8411670.184282
GH1_2)5.382641)4.663071)1.133139)0.389631
accepted什么意思中文GH1_3.4)3.230279)2.706827)0.660725)0.349572
GH1_4.4)1.936141)1.671905)0.7950150.330309
VT2_1–)1.704222–)7.001461
VT2_2–)1.355533–)5.031671
VT2_3–)0.262164–)4.012001
VT2_4–)0.150904–)2.677302
VT2_5–0.150005–)1.396547
VT4_1)2.301203–)6.694192–
VT4_2)1.673615–)6.555417–
VT4_3)1.217702–)4.965228–
VT4_4)0.849186–)2.403254–
VT4_5)0.495087–)1.041427–
SF1_1  2.955278–)14.617923–
SF1_2  1.116653–)12.142296–
SF1_3  1.433979–)7.841254–
SF1_40.861761–)4.676580–
SF2_1–0.286656–)8.236227
SF2_2–)0.189464–)6.857423
SF2_3–0.193895–)5.284785
SF2_4–0.482796–)3.301877
RE1_1  2.468990–)6.099051–
RE2_1–  2.747609–)6.981024
RE3_1  1.642657  2.143392)5.120612)5.946570
MH3_10.486081  2.865890)8.496928)8.255860
MH3_2  1.644377  3.500893)8.257450)6.883770
MH3_30.696675  2.694178)6.255882)5.404594
MH3_40.864621  2.333822)4.238056)3.439909
MH3_50.774435  1.609226)2.544268)1.943186
MH4_10.851938  4.534201)12.868018)15.794343
MH4_2)0.119061  2.494064)9.187208)12.925241
MH4_3  1.319095  2.212045)7.247869)9.157472

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