Compute fraction in equipoise

`computeEquipoise(data, equipoiseBounds = c(0.3, 0.7))`

## Arguments

- data
A data frame with at least the two columns described below.

- equipoiseBounds
The bounds on the preference score to determine whether a subject is in
equipoise.

## Value

A numeric value (fraction in equipoise) between 0 and 1.

## Details

Computes the fraction of the population (the union of the target and comparator cohorts) who are in clinical
equipoise (i.e. who had a reasonable chance of receiving either target or comparator, based on the baseline
characteristics).

The data frame should have a least the following two columns:

## References

Walker AM, Patrick AR, Lauer MS, Hornbrook MC, Marin MG, Platt R, Roger VL, Stang P, and
Schneeweiss S. (2013) A tool for assessing the feasibility of comparative effectiveness research,
Comparative Effective Research, 3, 11-20