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The Wald power and its quadratic approximation for logistic regression with a binary covariate, α = 0.05, Pr(y = 1|β = 0) = 0.25, Pr(x = 1) = 0.2, and n = 100. The Wald power falls at β = −2.4. Simulations (▲) are good match of the power approximation especially for positive alternatives (Nexp=5,000).
