Using the standard α = 0.05, sample size = 31, observed false positive (TI+|CXR-) rate =0.38 and the observed false negative (TI-|CXR+) rate = 0.20, the power (β-1) for the test applied to the overall population was calculated at 0.26. In order to achieve a power of 0.80 with the conditions encountered in this study, we would require 138 patients.