different times, and as a result the circumstances and treatment they encounter may differ. The possibility of such differences implies that the frequency of adverse treatment of minority testers, the gross measure, may capture differences that do not represent discrimination. In addition, testers are paired only on gender and age, and therefore may differ on many characteristics that might influence behavior during a test. This second problem may exacerbate the error in gross adverse treatment as a measure of discrimination while creating the potential for more severe biases in the analysis. Specifically, the populations of white and minority testers may differ systematically on characteristics that influence treatment. If so, the net and gross measures capture a combination of discrimination and the effect of racial differences in unobserved tester characteristics.
The 2000 HDS is attempting to address these issues. To the author's knowledge, Phase I of this study is the first paired-testing effort that records actual tester characteristics and makes those characteristics available for analysis. The characteristics collected include employment status and history, education level, individual and household income, household structure, and experience as a home seeker. Earlier research by Heckman and Siegelman (1993) and Ondrich et al. (2000, 2001) found only limited evidence that tester characteristics affect treatment. The data analyzed in these studies, however, contain no information about testers beyond an identification number, and these analyses were based on examining the experiences of pairs of testers who conducted multiple tests together. In HDS 2000, the analysis will exploit the information on actual tester characteristics, as well as test characteristics such as the attributes of the advertised unit and observed circumstances during a tester's visit, to determine whether these factors influence treatment and whether such influences affect observed net and gross adverse treatment.
Finally, Phase II of the 2000 HDS will include three-person or triplet tests to examine the influence of random differences between visits and testers on observed adverse treatment. These tests will take two forms: minority-white-white and white-minority-minority. The form will be randomized over tests. This approach will minimize noise by limiting the time between same-race visits while also ensuring that the first two visits of each triplet will yield a standard paired test.