Comparing Two Proportional Data Samples (95% Confidence)

We must calculate a test value Z_t.

x₁ = number of defects (or whatever) in sample #1

x₂ = number of defects (or same as above) in sample #2

absolute proportion difference (no minus sign in difference)

n₁ = size of sample #1

n₂ = size of sample #2

If Z_t > 1.96, then we can say with a 95% confidence that the two samples are significantly different.