An example of a coded sexual history. More than 18,000 sexual histories were collected between 1938 and 1963 by Alfred Kinsey and three other institute researchers. All were obtained through personal interviews. Each area on the coded form represented one aspect of an in-depth interview of 350 questions. The meaning of each symbol varied depending on its position on the form. To ensure confidentiality, a key for the code was never written down; researchers were taught the code verbally. Learning the code required months of practice. In scope, detail, method of interviewing, and number and variety of cross-checks, the Kinsey methodology was groundbreaking for sex research.