Sampling Distribution of the Difference Between Two Proportions (2 of 2)


For this example, the mean of the sampling distribution of p1 - p2 is:

μ= π1 - π2 = 0.8 - 0.4 = 0.4.

The standard error is:

= 0 .133.

The solution to the problem is the probability that p1 - p2 is less than or equal to 0. The number of standard deviations above the mean associated with a difference in proportions of 0 is:

formula for se

From z table it can be determined that only 0.0013 of the time would p1 - p2 be 3.01 or more standard deviations below the mean.