# Create a design for mediation analysis

Source:`R/mediation_analysis_designer.R`

`mediation_analysis_designer.Rd`

A mediation analysis design that examines the effect of treatment (Z) on mediator (M) and the effect of mediator (M) on outcome (Y) (given Z=0) as well as direct effect of treatment (Z) on outcome (Y) (given M=0). Analysis is implemented using an interacted regression model. Note this model is not guaranteed to be unbiased despite randomization of Z because of possible violations of sequential ignorability.

## Usage

```
mediation_analysis_designer(
N = 200,
a = 1,
b = 0.4,
c = 0,
d = 0.5,
rho = 0,
args_to_fix = NULL
)
```

## Arguments

- N
An integer. Size of sample.

- a
A number. Parameter governing effect of treatment (Z) on mediator (M).

- b
A number. Effect of mediator (M) on outcome (Y) when Z = 0.

- c
A number. Interaction between mediator (M) and (Z) for outcome (Y).

- d
A number. Direct effect of treatment (Z) on outcome (Y), when M = 0.

- rho
A number in [-1,1]. Correlation between mediator (M) and outcome (Y) error terms. Non zero correlation implies a violation of sequential ignorability.

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

## Details

See vignette online.

## Examples

```
# Generate a mediation analysis design using default arguments:
mediation_1 <- mediation_analysis_designer()
draw_estimands(mediation_1)
#> inquiry estimand
#> 1 FirstStage 0.325
#> 2 Indirect_0 0.400
#> 3 Indirect_1 0.400
#> 4 Controlled_Direct_0 0.500
#> 5 Controlled_Direct_1 0.500
#> 6 Natural_Direct_0 0.500
#> 7 Natural_Direct_1 0.500
if (FALSE) {
diagnose_design(mediation_1, sims = 1000)
}
# A design with a violation of sequential ignorability and heterogeneous effects:
mediation_2 <- mediation_analysis_designer(a = 1, rho = .5, c = 1, d = .75)
draw_estimands(mediation_2)
#> inquiry estimand
#> 1 FirstStage 0.345
#> 2 Indirect_0 0.400
#> 3 Indirect_1 1.400
#> 4 Controlled_Direct_0 0.750
#> 5 Controlled_Direct_1 1.750
#> 6 Natural_Direct_0 1.265
#> 7 Natural_Direct_1 1.610
if (FALSE) {
diagnose_design(mediation_2, sims = 1000)
}
```