These samples were also used for the 1996 and 1997 National Youth Gang Surveys. In previous surveys, the response rate for cities with populations of more than 150,000 has been as high as 91.3 percent. The response rate of those cities to the 1995 National Youth Gang Survey was estimated to be 74.5 percent. All of the above computations for the proposed sample size assumed a response rate of 75 percent. N is the true population size.
P is the true proportion of the population with a specific characteristic.
All the terms in the computing formula are presented in a form equivalent to those in Cochran's formula. An error rate d was computed as 5 percent. The probability of an estimated error being greater than d used in the computations above is .05.