The effective sample size is the sum of the harmonic means of the number units in treatment and control for each matched group. For k matched pairs, the effective sample size is k. As matched groups become more unbalanced, the effective sample size decreases.

## Usage

```
effectiveSampleSize(x, z = NULL)
# S3 method for factor
effectiveSampleSize(x, z = NULL)
# S3 method for default
effectiveSampleSize(x, z = NULL)
# S3 method for table
effectiveSampleSize(x, z = NULL)
```