# Multiple comparisons problem

Hi,

I have a question about correcting for multiple comparisons. My question is: for exactly how many tests should I correct in the scenario below? I can't seem to wrap my head around it.

Background: I’m testing for differences between groups A (patient group) and B (control group) in variable X. Variable X is a biological variable and is present in the left and right side of the body. Variable Y is a score on a test.

Step 1. Is there a significant difference within groups in (the weight of) left and right variable X?
For this purpose will conduct two paired sample t-tests

If I find a significant difference in step 1, then I will continue with both step 2A and 2B. If I don’t find a significant difference in step 1, then I will only continu with step 2C.

Step 2A. Is there a significant difference between groups in (the weight of) left variable X?
For this purpose I will conduct a independent t-test

Step 2B. Is there a significant difference between groups in (the weight of) right variable X?
For this purpose I will conduct a independent t-test

Step 2C. Is there a significant difference between groups in (the weight of) total variable X (= weight left + right variable X)?
For this purpose I will conduct a independent t-test

After step 2, and depending on the outcome in step 1 (significant, or not significant differences within groups), I will continue with both step 3A and 3B, or only step 3C.

Step 3A. Is there a significant correlation between (the weight of) left variable X in group A and variable Y?
For this purpose I will conduct a Pearson correlation

Step 3B. Is there a significant correlation between (the weight of) right variable X in group A and variable Y?
For this purpose I will conduct a Pearson correlation

Step 3C. Is there a significant correlation between (the weight of) total variable X in group A and variable Y?
For this purpose I will conduct a Pearson correlation

Thank you!

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