Despite the advantages of a large population of women ranging from age 50 to 104 years from throughout the United States, this study has some limitations. First, NORA included only women with personal physicians and excluded women who had a prior diagnosis of osteoporosis or were receiving specific treatment for osteoporosis. Therefore, NORA women may be healthier, with lower fracture rates and better BMD, than the US population. Second, peripheral devices were used to assess BMD in NORA, and comparability of these peripheral BMD test to the gold standard measurements of central hip and spine BMD is still under study. However, the WHO diagnostic criteria were established based on central (hip and spine) and peripheral (forearm) BMD measurement devices.21 T scores obtained by peripheral devices may not always be as low as T scores determined from central DXA devices, resulting in prevalences of WHO-defined osteoporosis using peripheral device–specific databases of 3% to 14%, compared with prevalences based on hip measurements for white women of 16% to 20%.34- 35 The discrepancies between T-score calculations among various BMD devices are well recognized and exist among different central DXA skeletal sites and devices as well.36- 40 As previously reported, prediction of fracture risk in NORA, including risk of hip fracture, with peripheral BMD measurements was similar to that reported in other studies12,23 with hip BMD measurements. Third, fractures in NORA were self-reported, without radiological confirmation, so fractures may have been overestimated (eg, sprains or arthritis reported as fractures) or underestimated (unrecognized or subclinical fractures). It has previously been shown, however, that self-report of fractures is generally reliable.41- 43 Because most spine fractures are asymptomatic or at least unrecognized, NORA cannot address the value of risk factors or peripheral BMD to predict nonclinical spine fractures. Over the long term, clinical and subclinical vertebral fractures are associated with increased morbidity and mortality.4,44 Finally, the data in this analysis are derived from information from white postmenopausal women, and generalization to other ethnic groups should be made with caution, if at all, until analyses from those groups become available.