Measurement invariance across chronic conditions: a systematic review and an empirical investigation of the Health Education Impact Questionnaire (heiQ™).
BACKGROUND
To examine whether lack of measurement invariance (MI) influences mean comparisons among different disease groups, this paper provides (1) a systematic review of MI in generic constructs across chronic conditions and (2) an empirical analysis of MI in the Health Education Impact Questionnaire (heiQ™).


METHODS
(1) We searched for studies of MI among different chronic conditions in online databases. (2) Multigroup confirmatory factor analyses were used to study MI among five chronic conditions (orthopedic condition, rheumatism, asthma, COPD, cancer) in the heiQ™ with N = 1404 rehabilitation inpatients. Impact on latent and composite mean differences was examined.


RESULTS
(1) A total of 30 relevant studies suggested that about one in three items lacked MI. However, only four studies examined impact on latent mean differences. Scale means were only affected in one of these three studies. (2) Across the eight heiQ™ scales, seven scales had items with lack of MI in at least one disease group. However, in only two heiQ™ scales were some latent or composite mean differences affected.


CONCLUSIONS
Lack of MI among disease groups is common and may have a relevant influence on mean comparisons when using generic instruments. Therefore, when comparing disease groups, tests of MI should be implemented. More studies of MI and according impact on mean differences in generic questionnaires are needed.
Department of Medical Psychology and Psychotherapy, Medical Sociology and Rehabilitation Sciences Section, University of Würzburg, Klinikstr, 3, D-97070 Wuerzburg, Germany. m.schuler@uni-wuerzburg.de.
Michael
M
Schuler
Gunda
G
Musekamp
Jürgen
J
Bengel
Sandra
S
Nolte
Richard H
RH
Osborne
Hermann
H
Faller
D001249:Asthma / Q000523:psychology; D002908:Chronic Disease / Q000523:psychology*; D036262:Empirical Research; D005163:Factor Analysis, Statistical; D006266:Health Education / Q000706:statistics & numerical data; D006801:Humans; D007592:Joint Diseases / Q000523:psychology; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000523:psychology; D029424:Pulmonary Disease, Chronic Obstructive / Q000523:psychology; D012216:Rheumatic Diseases / Q000523:psychology; D012737:Sex Factors; D011795:Surveys and Questionnaires