Your first taste of statistical inference. Using the sampling distribution of a sample proportion, you'll build confidence intervals and run significance tests for one and two population proportions, reason about Type I and Type II errors and power, and finish with chi-square tests for two-way tables.
Six ways to master Unit 3 — pick whichever fits how you like to study.
All 15 topics from the College Board CED, in order.
Unit 3 is where AP Statistics turns from describing data to drawing conclusions from it. Everything rests on the sampling distribution of a sample proportion p̂, which is approximately normal with mean p and standard deviation √(p(1−p)/n) when the conditions are met. From that foundation you build the two forms of inference: a confidence interval (estimate ± margin of error) that gives a plausible range for the true proportion, and a significance test that weighs evidence against a null hypothesis using a test statistic and a p-value.
You'll learn to state hypotheses, check the Random, 10%, and Large Counts conditions, interpret intervals and p-values in context, and reason carefully about Type I and Type II errors and the power of a test. The unit then extends every idea to two proportions (including the pooled proportion for tests) and closes with the chi-square test for homogeneity or independence, which compares distributions across the cells of a two-way table.
This unit is 15–25% of the AP Statistics exam and takes about 30 class periods. The four statistical practices below run through every topic: