I have multiple RNA-seq datasets in a meta-analysis. All of those datasets are TPM normalized. However, one or two are also log2 transformed.

I don't understand what this transformation does, and how can it affect the analysis?

Can I still compare regular TPM to transformed TPM?

Quote from one of the articles:

" TPM values were log2 transformed for further analysis of individual genes or standardized gene pathway signature scores. Briefly, for each gene, we calculated the mean expression and s.d. across samples. Then, we subtracted the mean and divided by the s.d. to standardize the gene score to be centered at zero with units of s.d. (z-score)."

Thanks!