Example: Low Power

Power and Sample Size

Test for Two Proportions

Testing proportion 1 = proportion 2 (versus not =)

Calculating power for:

proportion 1 = 0.55 and proportion 2 = 0.70

Alpha = 0.05 Difference = -0.15

Sample

Size Power

60 0.4366

70 0.4911

80 0.5421 *Sample size = # in EACH group