The post is incorrect as is: the power is indeed the proportion of times you correctly reject the null hypothesis when it is false, but the probability of making a Type II error is **one minus** the power of the test. With a power of 0.104, you fail to reject the null 89.6% of the time, not 10%... Misleading statements throughout the post:

> The probability of making a Type 2 error is called the power of a statistical hypothesis test.

> The tables tell you that (with these parameter values) the two-sided t test will commit a Type 2 error about 10% of the time (power=0.104) at the α=0.05 significance level. So we got "unlucky" when the simulated sample failed to reject the null hypothesis. Apparently, this only happens for 10% of random samples. In 9 out of 10 random samples, the t test will conclude that the sample comes from populations that have different means.

> For random samples from the specified distributions, PROC POWER shows that the probability that the t test will commit a Type 2 error is 0.1.