Requirements of the Ota Hip Fracture Prediction Model

T his appendix describes the assumptions used in OTA’s analysis of the impact of hormone replacement therapy (HRT) on hip fractures. OTA’s model assumes that HRT affects fracture risk through its impact on bone mass as measured by bone mineral density (BMD). The rationale for this assumption is twofold. First, the causal relationship between HRT and bone loss is well-established and precisely estimated, at least in the short-run. In contrast, the evidence of a direct relationship between HRT and fracture rests on studies with relatively weak designs that do not lend themselves readily to precise estimates of effect size. (See appendices B and C.) Second, the relationship between BMD measured at each age and the risk of hip fracture has been quantified in some recently reported studies.