4 The test statistic for this hypothesis test is the Z-score of the observed difference, P - P. A Compute the pooled proportion, p. p = With the pooled proportion, we estimate the standard error of differences. p(] - p) p(] - p 0.856(1 - 0.856) 0.856(1- 0.856) S + = + P : 825 861 = 0.017 - Pb