The use of "and" in bioinformatics literature

Question

[I0110]

Sorry, this is basically an English problem.

I am reading a paper which mentioned they normalized and log2 transformed their microarray data. Does that imply any relationship in time? I meant: did they normalize the data first then log2 transform the data?

Thanks!

Answer 1

[Ahill]

The "and" may not guarantee it was normalized first and log2-transformed second... Either approach could have been used, so if the order is important to you I would look more closely at the methods section of the paper for the details of the algorithms used. Example: for Affy oligo arrays, MAS5 methodology would effectively normalize on the linear scale first, and then analysts might often log2-transform afterwards, before doing differential analysis. For other more recent/common methods, normalizations might be applied after log2-transformation.

[I0110]

I really did not know that normalization could be done before log2-transformation. Thanks for sharing the knowledge, Ahill.