Confidence Intervals & Hypothesis Testing (5 of 5)

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Next section: Following a non significant finding


Now, consider the 95% confidence interval:

6 ≤ μ₁ - μ₂ ≤ 15.

Since zero is not in the interval, the null hypothesis that μ₁ - μ₂ = 0 can be rejected at the 0.05 level. Moreover, since all the values in the interval are positive, the direction of the effect can be inferred: μ₁ > μ₂.

Whenever a significance test rejects the null hypothesis that a parameter is zero, the confidence interval on that parameter will not contain zero. Therefore either all the values in the interval will be positive or all the values in the interval will be negative. In either case, the direction of the effect is known.

Next section: Following a non significant finding