RESEARCH METHODS HANDBOOK

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Contents	Introduction	Descriptive	Hypothesis	Tables	Appendix

Comparing Proportions From Two Independent Samples
(Z-test)

Assumptions

Independent random sampling

Nominal level data

Large sample size

State the Hypothesis Null Hypothesis (Ho): There is no difference between the proportion of one population (p1) and the proportion of another population (p2).

Alternate Hypothesis (Ha): There is a difference between the proportion of one population (p1) and the proportion of another population (p2).

Ha for 1-tailed test: The proportion of p1 is greater (or less) than the proportion of p2.

p1 > p2 or p1 < p2

Set the Rejection Criteria Establish alpha and 1-tailed or 2-tailed test

Use z-distribution table to estimate critical value

At alpha .05, 2-tailed test Zcv = 1.96

At alpha .05, 1-tailed test Zcv = 1.65

Compute the Test Statistic Standard error of the difference between two proportions

where

Test statistic

Decide Results of Null Hypothesis There is/is not a significant difference between the proportions of the two populations.

Example