**About me:**Medical student with

**minimal**statistical knowledge or research experience

**Question related to:**statistical regression/correlation analysis of a medical trial

**Trial design:**Double blind, randomized controlled trial. Placebo vs vitamin with a few months between baseline and follow-up measurements. Follow-up and baseline measurements are identical.

**Measurements performed, possibly relevant for answering my questions:**

In total 6 tests are performed twice. Once at baseline, once at follow-up.

*Insulin sensitivity testing;*2 tests.

- First provides 3 values usable for analysis (one of these is important, other 2 secondary)

- Second test provides 4 quite comparable values usable for analysis (difference are minor because of different calculation method)

*Vascular function testing;*4 tests.

- First provides one important useable value

- Second provides 4 values

- Third provides 3 values (1 important, 2 secondary)

- Fourth provides 4 equally important variables

**Important! Current situation:**

- Goal of study: 120 participants

- Current status: 13 participants included with baseline measurements taken, 8 of them have also completed follow-up measurements.

- Double blinded study, with no option to de-blind (until trial completion) to see effect of the vitamin. Solution for me:

**Looking at the correlations between insulin sensitivity (insulin resistance) and vascular function (vascular dysfunction).**

**What I did so far:**

*Baseline correlation*(N=13)

Using the 13 baseline measurements, I performed Spearman correlation (in SPSS) using all variables of insulin sensitivity and vascular function. I also included screening data such as BMI, age etc. I figured Pearson would be inferior because of the small sample size (and thus not a normal distribution).

*Follow-up/baseline difference*(N=8)

I made a separate database where I subtracted the baseline (BL) data from the follow-up (FU) data. This results in a database with both positive and negative values (because sometimes the values improved at follow-up, and sometimes they deteriorated).

I did this, because I want to know if there is a relationship between the change of insulin sensitivity and vascular functioning between BL and FU. In other words; does a decrease (between BL/FU) in insulin sensitivity cause an increase in vascular dysfunction?

To analyse this, I used the spearman correlation again. Also, I tried some linear regression analysis (in SPSS) on these numbers, using insulin sensitivity parameters as the independent variable.

**My questions:**

Regarding baseline correlation:

(1) Is Spearman correlation indeed the best (and easiest) way to assess the correlation between insulin resistance and vascular dysfunction in this situation?

Regarding the Follow-up/baseline difference analysis:

(2) Does it even make sense to use spearman correlation in this situation?

(3) Is linear regression the best way to analyse the difference between follow-up and baseline in this situation, using the subtracted data?

(4) Would it make sense to correct for age, sex or other variables in such a small sample size (N=8) with regression analysis?

General questions:

(5) After reading this, any other suggestions regarding the statistical analysis approach? Or any specific references I could use which deal with situations like this specifically?

Thank you in advance!

*PS. Note to administrators: this was my first time on this forum. After writing this relatively long thread (in latest version of Google Chrome) and then clicking on preview after a decent amount of time spent on typing it prompts with a re-login because of an expired session. After logging in again, I got a white screen. Pressing back did not work. Everything I wrote disappeared. Very frustrating*

I wrote this post again in Word and then pasted it into the forum to prevent this from happening again. Known issue?

I wrote this post again in Word and then pasted it into the forum to prevent this from happening again. Known issue?

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