In the textbooks I have access to (and that discuss hypothesis testing for correlation), I only met examples, where the null-hypothesis was $rho=0$, and the alternative hypothesis was $rhone 0$. My question is about using a one-sided alternative hypothesis $rho>0$. Is this meaningful?

This question has been asked before, but it has not been answered. There was a comment next to the linked question, that said that the null-hypothesis should be $rhole 0$ in case we would like a one-sided alternative hypothesis, but I have problems with this comment. As I understand, the t-distribution that is used for testing the correlation coefficient is only valid when $rho=0$, so we have no choice, but using this as the null-hypothesis.

So, to summarize: can we test $H_0:rho=0$ against $H_1:rho>0$ using $Rsqrt{dfrac{n-2}{1-R^2}}$ and the t-distribution with degree of freedom $n-2$?

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#### Best Answer

Yes. Instead of using a two-sided critical value from a t-distribution with $n-2$ degrees of freedom (e.g., $pm 2.09$ for $n=22$ and $alpha=.05$, two-sided), you would use just the upper critical value (e.g., $+1.72$ for $n=22$ and $alpha=.05$, one-sided).

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