This report presents the findings of a research study, conducted by the College of the Mainland (COM) as a subcontractor for Project FOLLOW-UP, designed to test the accuracy of random sampling and to measure non-response bias in mail surveys. In 1975, a computer-generated random sample of 500 students was drawn from a population of 1,256 students who had attended COM in the spring of 1972. A 48% response to a follow-up survey of the sample was achieved. A random subsample of 70 non-respondents was drawn and interviews were conducted with 56 who could be located as a validity check. A similar survey of spring 1973 students conducted in 1976 resulted in a 42% response rate and a random subsample of 78 non-respondents was drawn for interviewing. The total samples and total populations showed no significant differences on variables of age, sex, and GPA in either year. However, significant differences between mail-respondents and the total sample were found in terms of age and GPA (grade point average) but not sex in the first year, and in terms of GPA in the second year. Consistent differences were also found between mail-respondents and total populations and between the mail-respondents and interview samples. Sampling methods are reviewed, and causes and implications of non-response bias are discussed. Alternative bias correction methods are suggested. Study materials, survey instruments, and resultant data are appended. (JDS)