ABSTRACT
This chapter starts with the history of the 1946 National Survey of Health and Development which was the first national cohort to be studied in any country. The problems encountered in obtaining the sample, collecting information and estimating bias are described and suggestions are made for improving the design of future studies of this type. Some results, published and unpublished, which show the value of collecting data for the same individuals over time are presented, and then the chapter discusses some of the criticisms that have been made in recent years of cohort studies. Finally, it gives reasons for believing that in an evolving society, we cannot afford to be without a series of cohort studies strategically placed in relation to major changes in social policy. Another criticism of cohort studies is that the data collected take so long to process that they are out of date when written up.
