Chapter 4: the study design for a survey of american sexual behaviour. A study began in 1988 to talk about sex. For many sex is considered to be extremely private matter or to be discussed with close friends or intimates only. Everyone has different sexual lives and experiences (s & m/role-play) Normal sex is off limits because it is too ordinary, trivial, and self-evident to deserve attention to the study. Most of the problems in the survey involved in participation from people (confidentiality, ect. ) Probability sampling: sampling where every member of a clearly specified population has a known probability of selection. It is highly developed practical application of statistical theory to the problem of selecting a sample. The bigger, the higher the precision of it estimates. There may be errors too in the sampling. Door to door/ give a letter in advance about the survey. Interviewer needs to be fully persuaded about the legitimate and importance of the research.