You absolutely can! There are different ways to estimate a composite score like this; we describe a number of them in this paper: Article Assessing Change in Intervention Research: The Benefits of C...

Hopefully that helps!

This is a very valuable resource. Thank you very much for that. Considering my variables and context, taking the average will be the most appropriate approach I think. However, because I have 1 reaction time and 3 accuracy data at different ranges. Because of that, I will transform them into Z-scores before taking the average. Do you think that this is an appropriate approach? Should I also consider, for example, log transformation (I encountered a few applications like this) before z transformation? Do you have any other recommendations?

Sincerely thank you for your previous answer and in advance.

I think transforming the variables to Z-scores so they are on the same scale before averaging is an appropriate approach. For an inhibitory control measure, we used this approach to create a composite (latency variable and ordinal variable). The variables were significantly correlated. Creating the composite better conceptualized and captured the variability in performance .

Thank you for sharing your experience dear Holley Pitts Arnold,

I will surely follow your recommendation.

That's a really interesting question, and I think it depends on the research question. To show the development of executive functions over a period of time, it is possible to calculate a sum score or composite score. If you want to explain differences and similarities in the development of different functions, of course, differentiation is essential. Have the unity-diversity framework of EFs in mind when thinking about a sum score.

Here is a paper where I read about a sum score:

10.1016/j.psychsport.2020.101677