Transforming Negatively Skewed Independent Groups


New Member
I have two independent groups, (roughly 30 in each) – and their performance on 3 different tasks, there are 10 scores in total for each group.

The majority of them are negatively skewed so I know I have to reflect the data before I transform it – if the two groups have different maximum scores, do I use different maximums in the transformation formula or do I use the maximum overall?

Group 1 – Maximum = 36
Group 2 – Maximum = 39

So do I do
A) log10(40-Var) – for both groups
B) log10(37-Var) – for Group 1, and log10(40-Var) for group 2

And if I am later going to calculate a composite score, do I need to use the same transformation for all of the scores?

There are also a couple of outcomes where the data is negatively skewed for one group and positively skewed for the other – how do I deal with this?

Any help would be massively appreciated :)