Survey evidence is often introduced in court cases involving trademark violation and employment discrimination. There has been controversy, however, about whether non probability samples are acceptable as evidence in litigation. Jacoby and Handlin (1991) selected 26 from a list of 1285 scholarly journals in the social and behavioral sciences. They examined all articles published during 1988 for the selected journals, and recorded (1) the number of articles in the journal that described empirical research from a survey (they excluded articles in which the authors analyzed survey data which had been collected by someone else) and (2) the total number of articles for each journal which used probability sampling, non probability sampling, or for which the sampling method could not be determined. The data are in file journal.dat.
a. Explain why this is a cluster sample.
b. Estimate the proportion of articles in the 1285 journals that use non probability sampling, and give the standard error of your estimate.