The fourth of a series of reports on the study, Mental Retardation in a Canadian Province, the document covers the initial months of field data gathering in Prince Edward Island, April to September 1969. The major objectives of the study, to describe and explore the most suitable definition of retardation for a Canadian population and to report on the prevalence of mental retardation in a geographically defined population, are stated and further broken down into null hypotheses. Problems involved in selecting the sample population and data on the final sample, the battery of instruments administered, staff selection and training, the interview process, and the use of publicity to introduce and support the project are described. Professional interest in the study is mentioned with the conclusion that the study can fill an important research void. (RJ)