Calculate selection intensity under an assumption of pairwise epistasis between pairs of variants. CompoundVariantSets are supported.

## Usage

```
ces_epistasis(
cesa = NULL,
variants = NULL,
samples = character(),
run_name = "auto",
cores = 1,
conf = 0.95,
return_fit = FALSE
)
```

## Arguments

- cesa
CESAnalysis

- variants
To test pairs of variants, supply a list where each element is a 2-length vector of CES-style variant IDs. Alternatively (and often more usefully), supply a CompoundVariantSet (see

`define_compound_variants()`

) to test all pairs of compound variants in the set.- samples
Which samples to include in inference. Defaults to all samples. Can be a vector of Unique_Patient_Identifiers, or a data.table containing rows from the CESAnalysis sample table.

- run_name
Optionally, a name to identify the current run.

- cores
number of cores for parallel processing of variant pairs

- conf
confidence interval size from 0 to 1 (.95 -> 95%); NULL skips calculation, reducing runtime.

- return_fit
TRUE/FALSE (default FALSE): Embed epistatic model fits for each variant pair in a "fit" attribute of the epistasis results table. Use

`attr(my_results, 'fit')`

to access the list of fitted models.

## Value

CESAnalysis with a table of epistatic inferences appended to list `[CESAnalysis]$epistasis`

. Some column definitions:

variant_A, variant_B: Names for the two variants or merged sets of variants in each epistatic inference. For brevity in the case of merged variant sets, we say that a sample with any variant in variant set A "has variant A."

ces_A0: Cancer effect (scaled selection coefficient) of variant A that acts in the absence of variant B.

ces_B0: Cancer effect of variant B that acts in the absence of variant A.

ces_A_on_B: Cancer effect of variant A that acts when a sample already has variant B.

ces_B_on_A: Cancer effect of variant B that acts when a sample already has variant A.

p_A_change: P-value of likelihood ratio test (LRT) that informs whether selection for variant A significantly changes after acquiring variant B. The LRT compares the likelihood of the full epistatic model to that of a reduced model in which ces_A0 and ces_A_on_B are set equal. The p-value is the probability, under the reduced model, of the likelihood ratio being greater than or equal to the ratio observed.

p_B_change: P-value of likelihood ratio test (LRT) that informs whether selection for variant B significantly changes after acquiring variant A. The LRT compares the likelihood of the full epistatic model to that of a reduced model in which ces_B0 and ces_B_on_A are set equal. The p-value is the probability, under the reduced model, of the likelihood ratio being greater than or equal to the ratio observed.

p_epistasis: P-value of likelihood ratio test that informs whether the epistatic model better explains the mutation data than a non-epistatic model in which selection for mutations in each variant are independent of the mutation status of the other variant. Quite often, p_epistasis will suggest a significant epistatic effect even though p_A_change and p_B_change do not suggest significant changes in selection for either variant individually. This is because the degree of co-occurrence can often be explained equally well by a strong change in selection for either variant.

expected_nAB_epistasis: The expected number of samples with both A and B mutated under the fitted epistatic model. Typically, this will be very close to the actual number of AB samples (nAB).

expected_nAB_null: The expected number of samples with both A and B mutated under a no-epistasis model.

AB_epistatic_ratio: The ratio

`expected_nAB_epistasis/expected_nAB_null`

. Useful to gauge the overall impact of epistatic interactions on the co-occurrence of variants A and B. Since the expectations take mutation rates into account, this ratio is a better indicator than the relative frequencies of A0, B0, AB, 00 in the data set.nA0, nB0, nAB, n00: Number of (included) samples with mutations in just A, just B, both A and B, and neither.

ces_A_null, ces_B_null: Cancer effects of A and B when estimated independently; that is, effects under a no-epistasis model.