Question regarding lib.sizes when using glmQLFit
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@steve-pederson-3490
Last seen 6 days ago
Australia

When using the Quasi-Likelihood dispersions via glmQLFit in edgeR, and providing a DGEList as input, the function glmQLFit.DGEList() explicitly passes the value lib.size = NULL to the lower-level function glmQLFit(). This forces the library sizes to be the column sums when passed eventually to the lower-level function .compressOffsets(). I'm really struggling to see the justification for this.

My situation is that I'm using sliding windows via the workflow presented at https://f1000research.com/articles/4-1080/v2 and as such, the library size is not the sum of the reads in each column. I would like to use the correct library sizes I have assigned to the lib.size element of my DGEList. Clearly, I can just write my own function to get around this. However, is this an intentional decision with solid reasoning that's beyond me, or just one that slipped through?

glmQLFit edgeR • 67 views
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Yunshun Chen • 690
@yunshun-chen-5451
Last seen 6 days ago
Australia

glmQLFit.DGEList() not only passes lib.size=NULL but also passes an offset obtained by getOffset() to the low-level function glmQLFit(). In your case, this offset would be computed using the corrected lib.size stored in your DGEList object. And offset always takes precedence over lib.size in the low-level function glmQLFit().

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Thanks Andy. That makes sense for sure.

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The precedence of offset over lib.size is documented on the glmQLFit help page.

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