Condition A has M=5, SD=1
Condition B has M=10, SD=1

If a two-tailed test gives p<.05, can you infer that Condition B was significantly higher than Condition A without conducting a one-tailed test?

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    $\begingroup$ Welcome. I fail to see how this question fits Psych & Neurosci. $\endgroup$ – AliceD May 4 '19 at 14:24


A two-tailed test simply corrects for the appropriate probability of observing a difference as large as you observe given the null hypothesis is true. This probability is twice the one-tailed probability (in effect, a two-tailed test with alpha=0.05 is the same as two one-tailed tests each with alpha=0.025). You do not need a one-tailed test to infer the direction. If there is a significant difference with a two-tailed test, it clearly must be in the direction of the observed difference.


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