For a one tailed test evaluating a treatment that is supposed to decrease scores,a researcher obtains t(8)= 1.90.For α = .05,the correct decision is to reject the null hypothesis.

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A one-tailed test means that we are only interested in one direction of the effect (in this case, a decrease in scores). The t-value of 1.90 is greater than the critical value of 1.860 (obtained from a t-table with 8 degrees of freedom and α = .05, using a one-tailed test). Therefore, we reject the null hypothesis and conclude that the treatment did have a statistically significant effect in decreasing scores.

For a One Tailed Test Evaluating a Treatment That Is