Linking the Iowa Women's Health Study cohort to Medicare data: linkage results and application to hip fracture.

This study linked the Iowa Women's Health Study cohort to Medicare administrative data and assessed the value of using Medicare and survey-based sources to study hip fracture incidence. The authors used Social Security number to combine the Iowa Women's Health Study cohort Medicare enrollment and claims data for 1986-2004. Hip fractures were identified from Medicare and follow-up-mail, survey-based sources. Estimates of hip fracture incidence after age 65 years and postfracture mortality were compared. The authors were able to match to Medicare 99.2% of the 40,978 Iowa Women's Health Study participants who survived to age 65 years. Although both Medicare and survey-based hip fracture incidence showed the expected positive association with age and negative association with body mass index, hip fracture incidence was considerably underestimated by self-report (2.61 per 1,000 person-years of observation vs. 4.20 per 1,000 person-years of observation from Medicare-based estimates). Similarly, 1-year postfracture mortality was significantly underestimated by survey-based measures (1% vs. 14% for Medicare-based estimates). Medicare data are an outstanding source of health care information to supplement for older cohorts that have identifiers such as Social Security numbers. These data are useful for studying clinically unambiguous and high morbidity and mortality conditions. They enable less-biased collection of health data.