BETA(direction of effect) sign flipping based on the coded allele - when doing meta analysis of different studies - explain?

Question

[iphoenix2100]

Hi all,

So I am doing this new analysis (meta) from different studies. In which I was asked

• to swap the coded and non-coded alleles
• and the direction/sign of the beta flipped

to make both consistent across studies.

I am not able to understand this part or the reason why it is being done. Can someone explain

Eg. Study 1:

SNP      Coded allele    Non coded allele   Beta
rs1      A               T                  -0.5465

Study 2

SNP      Coded allele    Non coded allele   Beta
rs1      A               T                  0.0345

Answer 1

[David W]

It sounds like whoever asked you to do this just wants you to make sure all the studies you are using in your meta-analysis coded in the same way. So, in your example, if one study set "T" to the coded allele, you''d flip the sign of the effect-size so the result can be used to calculate the odds-ratio for the T (and not A) allele?

Or is there something I'm missing?