This function uses a base rate (Control Event Rate, argument `cer`

) and a
Meaningful Change Definitions (MCD, argument `mcd`

) to compute the
corresponding Cohen's d. See Gruijters & Peters (2019) for details.

```
dMCD(
cer,
mcd = NULL,
eer = NULL,
plot = TRUE,
mcdOnX = FALSE,
plotResultValues = TRUE,
resultValueLineColor = "blue",
resultValueLineSize = 1,
returnLineLayerOnly = FALSE,
theme = ggplot2::theme_bw(),
highestPossibleEER = 0.999999999,
xLab = ifelse(mcdOnX, "Meaningful Change Definition", "Control Event Rate"),
yLab = "Cohen's d",
dist = "norm",
distArgs = list(),
distNS = "stats",
...
)
# S3 method for dMCD
print(x, ...)
```

- cer
The Control Event Rate (or base rate): how many people already perform the target behavior in the population (as a proportion)?

- mcd
The Meaningful Change Definitions: by which percentage (as a proportion) should the event rate increase to render an effect meaningful?

- eer
Instead of the MCD, it is also possible to specify the Experimental Event Rate (EER), in which case the MCD is computed by taking the difference with the CER.

- plot
Whether to show a plot.

- mcdOnX
Whether to plot the Meaningful Change Definition on the X axis (by default, the CER is plotted on the X axis).

- plotResultValues
Whether to plot the result values.

- resultValueLineColor, resultValueLineSize
If plotting the result values, lines of this color and size are used.

- returnLineLayerOnly
Whether to only return a layer with the plotted line (which can be used to quickly stack lines for different MCDs).

- theme
The

`ggplot2`

theme to use.- highestPossibleEER
The highest possible EER to include in the plot.

- xLab, yLab
The labels for the X and Y axes.

- dist, distArgs, distNS
Used to specify the distribution to use to convert between Cohen's d and the CER and EER. distArgs can be used to specify additional arguments to the corresponding

`q`

and`p`

functions, and distNS to specify the namespace (i.e. package) from where to get the distribution functions.- ...
Any additional arguments to dMCD are passed on to the

`ggplot2::geom_line`

used to draw the line showing the different Cohen's d values as a function of the base rate (or MCD) on the X axis. Additional arguments for the print method are passed on to the default print method.- x
The object to print (i.e. a result from a call to dMCD).

The Cohen's d value, optionally with a `ggplot2`

plot stored in an
attribute (which is only a `ggplot2`

layer if `returnLineLayerOnly=TRUE`

).

Gruijters, S. L. K., & Peters, G.-J. Y. (2020). Meaningful change
definitions: Sample size planning for experimental intervention research.
*PsyArXiv*. doi:10.31234/osf.io/jc295

```
dMCD(.2, .05);
#> mcd
#> cer 0.05
#> 0.2 0.1671315
```