In studying the effectiveness of different instructional practices or programs, it is possible that an outcome measure may be biased in favor of a particular practice or program because the overlap between the test and one program is greater than for the other(s). Two basic approaches for dealing with the overlap issue are reviewed. The first approach is a systematic analysis of curricula and tests to help guide test selection. A second approach to overlap is to measure the degree of overlap directly, and incorporate such a measure into the analysis. This approach could be used in conjunction with the first, or alone. Also reviewed are two ways to directly measure overlap which have been developed. The first involves teacher interviews or questionnaires. The second involves analyzing the curriculum to assess if information required by the test has been covered by the curriculum. The teacher interview approach reflects both informal in-class instruction and curriculum-based instruction, but it may also include the teacher's expectation about student competency. Both approaches do equally well in predicting final test performance. (Author/RL)