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March 17, 1993

Variability in Bone Mass Measurement

JAMA. 1993;269(11):1386. doi:10.1001/jama.1993.03500110054028

To the Editor.  —We read with great interest the recent article by Recker et al.1 The authors concluded that gain in bone mass occurs in healthy young women during the third decade of life, with the median gain (expressed as a percentage per decade) ranging from 4.8% (forearm) to 12.5% (total body). They used median values instead of means because "the distributions for rates of change in bone mineral were not gaussian."However, a closer look at their Table 2, which presents the percentage changes in bone mineral per decade, makes the conclusion questionable. Namely, the 95% confidence intervals (CIs) for these median gains in bone mineral are extremely large, including very high negative values. For example, the CI for the 4.8% median gain in the forearm bone mineral density was from —25.7% to 25.6%, indicating that in the population the actual change can be anything from very high