# Why does the one-sided T-test reject the Null Hypothesis while the two-sided doesn't?

I'm not that familiar with statistics, especially not with T-tests, however I need to apply a T-test for my dataset. My dataset is basically an observation of productivity over several weeks, where week 1 and 2 are considered as phase 1 and week 3 as phase 2. I'm comparing if there's a productivity increase between phase 1 and phase 2.

Now, the one-sided T-test rejects the Null hypothesis (with 90%), where the two sided does not reject the Null hypothesis (between 80% and 90%).

Could someone explain to me, what this behavior means and which result I should focus more on?

• Jun 23 at 15:25

Let say the significance level $$\alpha$$ is 0.05