How to handle mediation analysis (within participant design, two condition, three measurements)?

21 February 2022 3 842 Report

Hi,

I am currently working on a project where we examine the effect of an intervention on fatigue. The project has been carried out according to an one-group pre-test post-test design. I am uncertain about the best way to conduct a mediation analysis.

In our project we started with a 12week control period. So we have a baseline measurement at T0, and the pre-test measurement at T12. So we have two measurements for 1 condition. The following 12 weeks are the intervention period, and we have post-test measurement after these 12 weeks at T24.

Our outcome (fatigue) and potential mediators have been measured at all these three time points. We conducted a mediation analysis according to Montoya & Hayes (2017). However, this analysis only took into account the measurements at T12 and T24. So the baseline measurement is not considered at all. Now we are wondering, is this the correct way of conducting this analysis, or do we also need to include the baseline measurement? We had the following idea's

Conduct the analysis with T12 (pre-test) compared toT24 (post-test) as we did.
Conduct the analysis with the average of T12 and T0 (pre-test) compared to T24 (post-test).
Conduct two separate analyses, so compare T0 and T12, and compare T12 with T24.
Conduct an analysis to compare the change score (T12-T0) with the change score (T24-T12)

What would you guys do?

David Morse

Hello Marjin,

I believe that your team's decision to use M & Y values from T12 and T24 make the most sense for drawing inferences about potential mediation, given your description of the study.

You could, however, additionally explore the T0 to T12 changes in M & Y. Should it turn out that one or both change, just as a function of time, then this will necessarily require that you qualify any statements about the first analysis (T12 to T24). (In other words, is the T12-T24 analysis the influence of time--or possibly some ad hoc event during that specific time, the difference in X condition, or some combination?)

Good luck with your work.

David Eugene Booth

Next time plan your analysis before you collect your data.. Best wishes David Booth

Marijn Witziers

I agree with considering data analysis before data collection. However, I was not part of the team yet at time of data collection.

Thank you David for your answer! After some considerations with the team we indeed decided to perform an additional analysis to explore the possible changes between T0 and T12 in order to control for time.

How to compare two groups with only two measurements?

Enhanced Yellow Fluorescent Protein (Aequorea victoria) DNA sequence?

What kind of fluid could I use for a pitfall trap that also does not invalidate molecular testing?

What's the best way to measure growth rates in House sparrow chicks from day 2 to day 10?

Do we need to write protocol for a second study of a systematic review that has been registered and published?

How to increase a model accuracy ?

Do I need to do linear regression before running mediation analysis using PROCESS MACRO by Hayes ?

Sample dilution for quantitative analysis using ELISA?

Is There Any Feasible Method To Test Fluorescent Compounds Other Than Fluorescence Spectrometers ??

How to calculate average trend in maximum annual NDVI from MODIS?