Alternate-form health measures are useful for clinical trials or health services research requiring repeated administrations over a short interval of time. Further, by using alternate-form methodology, they can be utilized to estimate score reliability. Data from the Medical Outcomes Study were used to evaluate five alternate forms of the Short-Form 36-ltem Health Survey (SF-36) general mental health scale (MHI-5). Well-established psychometric criteria were used to select the best alternate form and to estimate the reliability of the MHI-5 using the alternate-form methodology. Although a considerable degree of comparability across the five alternate forms was observed for criteria pertaining to estimates of item-internal consistency and reliability, distributional characteristics of scales, tests of empirical validity, and score equivalence at the individual level, we recommend one alternate form that satisfied all evaluation criteria and did so better than any other alternate form. Using the alternate-form methodology of estimating reliability, results suggest that the internal-consistency method underestimates the reliability of the MHI-5 by 3%. The methodology presented here should prove useful to others interested in constructing and evaluating alternate forms, and the alternate form recommended here (MHI-5AF) should prove useful across many health status assessment applications.
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