Bone width (BW, cm), bone mineral density (BMD, g/cm) and bone mineral density (BMD, g/square cm) are three indexes to the mineral content of the bone. Since the ways, methods and instruments measurement are usually not the same, exact measurement of the three indexes could not be assured. Thus the results of data analysis might not keep with the facts. We treated the three indexes as latent variables, set up a linear structural relation model (LISREL) and hence confirmed the causation of osteoporosis.