Pitfalls in measuring the health status of Mexican Americans: comparative validity of the English and Spanish Sickness Impact Profile.

We tested a Spanish translation of the Sickness Impact Profile (SIP) in a clinical study of low back pain, which included non-Hispanic patients (Group I), Mexican Americans who used the English SIP (Group II), and Mexican Americans who used the Spanish SIP (Group III). The reliability and clinical validity of responses by these three groups were compared. Internal consistency of responses by all three groups was excellent ( Cronbach 's alpha for the overall SIP = .93 - .95). When construct validity was tested by correlating SIP scores with several clinical measures of disease severity, however, important differences emerged. Group I responses appeared to be highly valid, while group III responses did not; Group II responses appeared reasonably valid, but intermediate between the other groups. These differences appear unlikely to be due to clinical differences, interviewing, or translational problems and seem to parallel the groups' levels of "acculturation." It may be that certain aspects of acculturation, including familiarity with questionnaire research, critically affect the validity of responses to this questionnaire.