The model coefficients that are being tested for enrichment are the coefficients from the zlmfit objects. With **A** as a ref, then positive coefficients in the `ZlmFit`

object means that the mean of **B** > mean of **A**. The GSEA is calculating the average `ZlmFit`

coefficient inside the set. So a positive Z-score in `gseaAfterBoot`

means that **B** > **A**, on average, in the gene set.

## Example

```
library(MAST)
package.version("MAST")
## "1.3.0"
data(vbetaFA)
vb1 = subset(vbetaFA, ncells==1)
vb1 = vb1[,freq(vb1)>.1][1:15,]
zf = zlm(~Stim.Condition, vb1)
coef(zf, 'D') #discrete components
boots = bootVcov1(zf, 5)
sets = list(A = 1:2, #positive coefficients
B = 3:6) #negative
gsea = gseaAfterBoot(zf, boots, sets, CoefficientHypothesis('Stim.ConditionUnstim'))
calcZ(gsea)[,,'Z'] #zscore is positive for A, negative for B
summary(gsea) #pretty-printer
```