External validity of a population-based study on osteoporosis and fracture
Background and purpose-Little is known about the characteristics of non-participants in epidemiological studies. We evaluated external validity by comparing fracture and mortality rate in participants and non-participants in a longitudinal study on risk factors for fracture. Methods - 1,604 randomly selected women, 75 years of age, were invited to attend a study on osteoporosis and fracture. 1,044