How it is to be determined that the microarray gene expression data is log transformed?

Question

[Shaurya Jauhari]

The gene-sample microarray dataset holds positive values throughout and of high magnitude. Although, my primary assumption is that the data isn't log transformed, but can I go a step further to consolidate my claim formally?

[Devon Ryan]

Is this something you downloaded from GEO or do you have the raw files (CEL or otherwise)? In the former case you can sometimes discern this by reading through the experiment details. In the latter case only certain normalization methods will produce log transformed data and you can just read the documentation for whichever function you're using.