# nnc

##### Numbers Needed for Change

This function computes the Numbers Needed for Change, and shows a
visualisation to illustrate them. `nnt`

is an alias for `nnc`

.

- Keywords
- utilities

##### Usage

```
nnc(d = NULL, cer = NULL, r = 1, n = NULL,
threshold = NULL, mean = 0, sd = 1,
poweredFor = NULL, thresholdSensitivity = NULL,
eventDesirable = TRUE, eventIfHigher = TRUE,
conf.level=.95,
d.ci = NULL, cer.ci = NULL, r.ci = NULL,
d.n = NULL, cer.n = NULL, r.n = NULL,
plot = TRUE, returnPlot = TRUE, silent = FALSE)
```

##### Arguments

- d
The value of Cohen's

*d*.- cer
The Control Event Rate.

- r
The correlation between the determinant and behavior (for mediated Numbers Needed for Change).

- n
The sample size.

- threshold
If the event rate is not available, a threshold value can be specified instead, which is then used in conjunction with the mean (

`mean`

) and standard deviation (`sd`

) and assuming a normal distribution to compute the event rate.- mean
The mean value, used to draw the plot, or, if no CER is provided but instead the threshold value, to compute the CER.

- sd
The standard deviation, used to draw the plot (and to compute the CER if a threshold value is supplied instead of the CER).

- poweredFor
The Cohen's

*d*value for which the study was powered. This expected Cohen's*d*value can be used to compute the threshold, which then in turn is used to compute the CER. To use this approach, also specify the mean and the standard deviation.- thresholdSensitivity
This argument can be used to provide a vector of potential threshold values, each of which is used to compute an NNC. This enables easy inspection of whether the value chosen as threshold matters much for the NNC.

- eventDesirable
Whether an event is desirable or undesirable.

- eventIfHigher
Whether scores above or below the threshold are considered 'an event'.

- conf.level
The confidence level of the confidence interval.

- d.ci
Instead of providing a point estimate for Cohen's

*d*, a confidence interval can be provided.- cer.ci
Instead of providing a point estimate for the Control Event Rate, a confidence interval can be provided.

- r.ci
Instead of providing a point estimate for the correlation, a confidence interval can be provided.

- d.n
In addition to providing a point estimate for Cohen's

*d*, a sample size can be provided; if it is, the confidence interval is computed.- cer.n
In addition to providing a point estimate for the Control Event Rate, a sample size can be provided; if it is, the confidence interval is computed.

- r.n
In addition to providing a point estimate for the correlation, a sample size can be provided; if it is, the confidence interval is computed.

- plot
Whether to generate and show the plot.

- returnPlot
Whether to return the plot (as an attribute), or to only display it.

- silent
Whether to suppress notifications.

##### Details

This function computes the Numbers Needed for Change. See Gruijters & Peters (2017) for details.

##### Value

The Numbers Needed for Change (NNC), potentially with a plot visualising the NNC in an attribute.

##### References

Gruijters, S. L. K., & Peters, G.-J. Y. (2017). Introducing the Numbers Needed for Change (NNC): A practical measure of effect size for intervention research.

##### Examples

```
# NOT RUN {
### Simple example
nnc(d=.4, cer=.3);
### Or for a scenario where events are undesirable, and the
### intervention effective (therefore having a negative value for d):
nnc(d=-.4, cer=.3, eventDesirable=FALSE);
# }
```

*Documentation reproduced from package userfriendlyscience, version 0.7.2, License: GPL (>= 3)*