Introduction: Measures of health status and physical function do not usually include a specific code for death. This can cause problems in longitudinal studies because analyses limited to survivors may bias the results. One approach is to recode the status variables to include a reasonable value for death. One method that has been used is to replace each scale value with the estimated probability that a person with this value will be “healthy”. “Healthy” has been defined as being above a particular threshold on the variable of interest one year later, or alternatively as being in excellent, very good, or good self-rated health in the same year. Transformation coefficients have been published for various health status measures, but the coefficients were estimated from data for older adults (usually older than 65).
Methods: Here, we used data from the Medical Expenditures Panel Survey (MEPS) to develop new age-specific coefficients for self-rated health, activities of daily living (ADL), instrumental activities of daily living (IADL), and the SF-12 physical function scale (PCS). We computed new age-specific transformations for ages 0 through 85 and compared the new transformations with published transformations for persons aged 65 and older.
Results: The transformed values were different at different ages, The new transformed values for persons 65 and over were remarkably similar to the published results, calculated from different datasets.
Conclusion: The new transformation equations should be particularly useful for studies involving persons younger than 65. For older persons, either the published equations or these new equations may be used.
Derleth, Ann M. and Diehr, Paula, "Age- and Sex-Specific Transformations of Health Status Measures to Incorporate Death" (June 2006). UW Biostatistics Working Paper Series. Working Paper 418.