A friend has performed a significance test of the null hypothesis that two means
ID: 3174741 • Letter: A
Question
A friend has performed a significance test of the null hypothesis that two means are equal. His report states that the null hypothesis is rejected in favor of the alternative that the first mean is larger than the second. In a presentation on his work, he notes that the first sample mean was larger than the second mean and this is why he chose this particular one-sided alternative.
(a) Explain what is wrong with your friend's procedure and why.
We should only choose a one-sided alternative if we have some reason to expect a specific directional outcome before looking at the sample results.
(b) Suppose he reported t = 1.50 with a P-value of 0.08. What is the correct P-value that he should report?
Explanation / Answer
ans=
A) a hypothesis test for a mean value, using a one-sample t-test. The test procedure is illustrated with examples for one- and two-tailed tests Because the null hypothesis is that the means are equal, you need to perform a two-sided test. You cannot perform a one-sided test just because one sample mean was larger than another
B)To convert from a one-sided to two-sided p-value, simply multiply by two. So the correct p-value is 0.08
2*0.08=0.16.