# DunnettTest: Dunnett's Test for Comparing Several Treatments With a... In DescTools: Tools for Descriptive Statistics

## Description

Performs Dunnett's test for comparing several treatments with a control.

## Usage

 ```1 2 3 4 5 6 7``` ```DunnettTest(x, ...) ## Default S3 method: DunnettTest(x, g, control = NULL, conf.level = 0.95, ...) ## S3 method for class 'formula' DunnettTest(formula, data, subset, na.action, ...) ```

## Arguments

 `x` a numeric vector of data values, or a list of numeric data vectors. `g` a vector or factor object giving the group for the corresponding elements of `x`. Ignored if `x` is a list. `control` the level of the control group against which the others should be tested. If there are multiple levels the calculation will be performed for every one. `conf.level` confidence level of the interval. `formula` a formula of the form `lhs ~ rhs` where `lhs` gives the data values and `rhs` the corresponding groups. `data` an optional matrix or data frame (or similar: see `model.frame`) containing the variables in the formula `formula`. By default the variables are taken from `environment(formula)`. `subset` an optional vector specifying a subset of observations to be used. `na.action` a function which indicates what should happen when the data contain `NA`s. Defaults to `getOption("na.action")`. `...` further arguments to be passed to or from methods.

## Details

`DunnettTest` does the post hoc pairwise multiple comparisons procedure.

If `x` is a list, its elements are taken as the samples to be compared, and hence have to be numeric data vectors. In this case, `g` is ignored, and one can simply use `DunnettTest(x)` to perform the test. If the samples are not yet contained in a list, use `DunnettTest(list(x, ...))`.

Otherwise, `x` must be a numeric data vector, and `g` must be a vector or factor object of the same length as `x` giving the group for the corresponding elements of `x`.

## Value

A list of class `c("PostHocTest")`, containing one matrix named after the control with columns `diff` giving the difference in the observed means, `lwr.ci` giving the lower end point of the interval, `upr.ci` giving the upper end point and `pval` giving the p-value after adjustment for the multiple comparisons.

There are print and plot methods for class `"PostHocTest"`. The plot method does not accept `xlab`, `ylab` or `main` arguments and creates its own values for each plot.

## Author(s)

Andri Signorell <[email protected]>, the interface is based on R-Core code

## References

Dunnett C. W. (1955) A multiple comparison procedure for comparing several treatments with a control, Journal of the American Statistical Association, 50:1096-1121.

`PostHocTest`

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24``` ```## Hollander & Wolfe (1973), 116. ## Mucociliary efficiency from the rate of removal of dust in normal ## subjects, subjects with obstructive airway disease, and subjects ## with asbestosis. x <- c(2.9, 3.0, 2.5, 2.6, 3.2) # normal subjects y <- c(3.8, 2.7, 4.0, 2.4) # with obstructive airway disease z <- c(2.8, 3.4, 3.7, 2.2, 2.0) # with asbestosis DunnettTest(list(x, y, z)) ## Equivalently, x <- c(x, y, z) g <- factor(rep(1:3, c(5, 4, 5)), labels = c("Normal subjects", "Subjects with obstructive airway disease", "Subjects with asbestosis")) DunnettTest(x, g) ## Formula interface boxplot(Ozone ~ Month, data = airquality) DunnettTest(Ozone ~ Month, data = airquality) DunnettTest(Ozone ~ Month, data = airquality, control="8", conf.level=0.9) ```

### Example output

```  Dunnett's test for comparing several treatments with a control :
95% family-wise confidence level

\$`1`
diff     lwr.ci    upr.ci   pval
2-1  0.385 -0.6901497 1.4601497 0.5832
3-1 -0.020 -1.0336608 0.9936608 0.9982

---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Dunnett's test for comparing several treatments with a control :
95% family-wise confidence level

\$`Normal subjects`
diff     lwr.ci
Subjects with obstructive airway disease-Normal subjects  0.385 -0.6901497
Subjects with asbestosis-Normal subjects                 -0.020 -1.0336608
upr.ci   pval
Subjects with obstructive airway disease-Normal subjects 1.4601497 0.5832
Subjects with asbestosis-Normal subjects                 0.9936608 0.9982

---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Dunnett's test for comparing several treatments with a control :
95% family-wise confidence level

\$`5`
diff    lwr.ci   upr.ci    pval
6-5  5.829060 -22.43792 34.09604 0.96467
7-5 35.500000  15.22870 55.77130 0.00011 ***
8-5 36.346154  16.07486 56.61745 9.7e-05 ***
9-5  7.832891 -11.90719 27.57297 0.73506

---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Dunnett's test for comparing several treatments with a control :
90% family-wise confidence level

\$`8`
diff    lwr.ci     upr.ci    pval
5-8 -36.3461538 -54.26925 -18.423062 7.5e-05 ***
6-8 -30.5170940 -55.50965  -5.524537  0.0298 *
7-8  -0.8461538 -18.76925  17.076938  0.9999
9-8 -28.5132626 -45.96667 -11.059853  0.0019 **

---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
```

DescTools documentation built on March 19, 2018, 9:03 a.m.