Produces a design in which an outcome Y is observed pre- and post-treatment. The design allows for individual post-treatment outcomes to be correlated with pre-treatment outcomes and for at-random missingness in the observation of post-treatment outcomes.

```
pretest_posttest_designer(
N = 100,
ate = 0.25,
sd_1 = 1,
sd_2 = 1,
rho = 0.5,
attrition_rate = 0.1,
args_to_fix = NULL
)
```

- N
An integer. Size of sample.

- ate
A number. Average treatment effect.

- sd_1
Nonnegative number. Standard deviation of period 1 shocks.

- sd_2
Nonnegative number. Standard deviation of period 2 shocks.

- rho
A number in [-1,1]. Correlation in outcomes between pre- and post-test.

- attrition_rate
A number in [0,1]. Proportion of respondents in pre-test data that appear in post-test data.

- args_to_fix
A character vector. Names of arguments to be args_to_fix in design.

A pretest-posttest design.

See vignette online.

```
# Generate a pre-test post-test design using default arguments:
pretest_posttest_design <- pretest_posttest_designer()
```