I am writing a grant, where we have a prospective cohort study and 4 hypotheses. Our hypotheses are directional, that is, we expect significantly increased values in hypothesis #1,2,3; and significantly decreased value on hypothesis #4 (compared with baseline at 3-month follow up post-intervention). We will be performing a pre-intervention measurement and 3 months after the intervention, the same measurements will be repeated.
Inherently, the intervention we will be performing is a routine procedure to alleviate symptoms (hypotheses 1-2-3-4). Therefore, unidirectional changes in our respective hypotheses are I believe justified. The preliminary data also indicate that the changes will be unidirectional. Since the hypotheses are not "significantly different values compared to baseline", but rather "significantly increased" for hypotheses #1-2-3, and "significantly decreased" for the hypothesis #4 following the intervention at 3-months, I am thinking that one-sided paired t-test is justified.
I use STATA to run the sample size calculations for the grant, and I will be using STATA for the stats analysis.
Am I right?
Many thanks in advance.