A statistical test for the detection of answer copying on multiple-choice tests is presented. The test is based on the idea that the answers of examinees to test items may be the result of three possible processes: (1) knowing, (2) guessing, and (3) copying, but that examinees who do not have access to the answers of other examinees can arrive at their answers only through the first two processes. This assumption leads to a distribution for the number of matched incorrect alternatives between the examinee suspected of copying and the examinee believed to be the source that belongs to a family of "shifted binomials." Power functions for the tests for several sets of parameter values are analyzed. An extension of the test to include matched numbers of correct alternatives would lead to improper statistical hypotheses.