Large Counts condition

The Large Counts condition checks that np is at least 10 and n(1-p) is at least 10, so the sampling distribution of p-hat is close to normal.

Large Counts is a sample size check: you need roughly 10 successes and 10 failures before you can treat the sampling distribution of p^\hat{p} (p-hat, the sample proportion) as normal; that is the textbook name for it, and the AP course framework calls the same check the normality condition. Which value of pp goes into the check depends on the procedure. A significance test has a hypothesized value, so you verify np010np_0 \ge 10 and n(1p0)10n(1-p_0) \ge 10 using p0p_0 (p-naught); a confidence interval has no hypothesized value, so you verify np^10n\hat{p} \ge 10 and n(1p^)10n(1-\hat{p}) \ge 10, which is just counting the observed successes and failures. Testing p0=0.25p_0 = 0.25 with n=60n = 60 passes, since np0=15np_0 = 15 and n(1p0)=45n(1-p_0) = 45.

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