The purpose of a study by Porcellini et al. (A-25) was to study the difference in CD4 cell response in patients taking highly active antiretroviral therapy (HAART, treatment 1) and patients taking HAART plus intermittent interleukin (IL-2, treatment 2). Another factor of interest was the HIVRNA plasma count at baseline of study. Subjects were classified as having fewer than 50 copies/ml

(plasma 1) or having 50 or more copies/ml (plasma 2). The outcome variable is the percent change in CD4 T cell count from baseline to 12 months of treatment. Can one conclude that there is a difference in the percent change in CD4 T cell count between the two treatments? The results are shown in the following table. Can one conclude that there is a difference in the percent change in CD4 T cell count between those who have fewer than 50/ml plasma copies of HIV-RNA and those who do not? Can one conclude that there is interaction between treatments and plasma levels? Let a ¼ :05 for each test.

Percent Change in CD4 T Cell Treatment Plasma 12:60 1 1 14:60 2 1 28.10 2 1 77.30 1 1 0:44 1 1 50.20 1 1 48.60 2 2 86.20 2 2 205.80 1 2 100.00 1 2 34.30 1 2 82.40 1 2 118.30 1 2 Source: Data provided courtesy of Simona Porcellini, Guiliana Vallanti, Silvia Nozza, Guido Poli, Adriano Lazzarin, Guiseppe Tabussi, and Antonio Grassia, “Improved Thymopoietic Potential in Aviremic HIV Infected Individuals with HAART by Intermittent IL-2 Administration,” AIDS, 17 (2003), 1621–1630.