A critique of survey methods used to measure the occurrence of osteomalacia and rickets in the United Kingdom

In order to demonstrate that a preventive campaign reduces the prevalence of rickets and osteomalacia, a reliable and precise estimate of the prevalence of these diseases in the population in which the campaign is to be evaluated is needed. This will involve choosing a method of identifying cases of rickets and osteomalacia which has been properly standardized for inter- and intra-observer variation and whose sensitivity and specificity in identifying cases of rickets and osteomalacia are known. Samples have not only to be representative of the population chosen but also sufficiently large to allow acceptable confidence limits to be attached to the prevalence estimates. So far, surveys purporting to measure the occurrence of osteomalacia and rickets have failed to tackle these problems adequately.