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Help choosing truth sensitivity

sp580sp580 GermanyMember
edited March 10 in Ask the GATK team

Hello,

I am trying to decide which set of SNPs to use for my downstream analyses. I need to have > 1SNP per Kbp to detect signatures of selection (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4611237/). The tranches that achieve this SNP density start from 80% truth sensitivity.
Looking at the tranches plot , tranches 80-90 are reasonable based on the novel TiTv ratio for the species I am working with.

However, the fraction of false positives (Target TiTv ratio = 2) might be too high for these tranches (0.2-0.25):

    | targetSensitivity|     nTP|     nFP| FP_fraction|
    |-----------------:|-------:|-------:|-----------:|
    |                60|  140491|    5357|       0.037|
    |                65|  200758|   10581|       0.050|
    |                70|  289547|   23544|       0.075|
    |                75|  303540|   76741|       0.202|
    |                80|  311006|   81051|       0.207|
    |                85|  322111|   90922|       0.220|
    |                90|  340943|  110478|       0.245|
    |                95|  377469|  340152|       0.474|
    |               100| 1479090| 2361373|       0.615|

But I am not really sure how to interpret this information. The way this makes sense to me is that if I use, for instance, tranche 85 as my final SNP subset, I would accept that each novel SNP has 22% chance of being a false positive. However, this corresponds to 90922 SNPs and 1% of the total SNP set, which I am willing to live with and move on with the analysis.

I would like to know if this interpretation correct and if you have any suggestions (i.e. would it make a big difference to choose tranche 90 instead of 85?).

Thanks!

Post edited by sp580 on

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