# cvSDDT: To calculate the critical constants for step-down Dunnett... In DunnettTests: Software implementation of step-down and step-up Dunnett test procedures

## Description

The function applies to testing problem with either t distributed test statistics or (approximately) normally distributed test statistics. The function accomodates both equally correlated and unequally correlated test statistics.

## Usage

 `1` ```cvSDDT(k,alpha=0.05,alternative="U",df = Inf,corr = 0.5,corr.matrix=NA) ```

## Arguments

 `k` Number of hypotheses to be tested, k≥ 2 and k≤ 16. `alpha` The pre-specified overall significance level, default=0.05. `alternative` The alternative hypothesis: "U"=upper one-sided test (default); "B"=two-sided test. For lower one-sided tail test, specify alternative="U" and use the negations of the return critical constants. `df` Degree of freedom of the t-test statistics. When (approximately) normally distributed test statistics are applied, set df=Inf (default). `corr` Specified for equally correlated test statistics, which is the common correlation between the test statistics, default=0.5. `corr.matrix` Specified for unequally correlated test statistics, which is the correlation matrix of the test statistics, default=NA.

## Value

Return a k-vector of critical constants from smallest to largest.

## Author(s)

FAN XIA <phoebexia@yahoo.com>

## References

Charles W Dunnett and Ajit C Tamhane. Step-down multiple tests for comparing treatments with a control in unbalanced one-way layouts. Statistics in Medicine, 10(6):939-947, 1991.

## Examples

 ```1 2 3 4 5 6 7 8``` ```#To test four hypotheses, the test statistics are #2.2 (H1), 2.7 (H2), 2.1(H3), 0.85(H4), respectively. #The test statistcis are equally correlated at 0.6 and have df=30. #At overall one-sided significance level 0.05, the critical constants are given by: cvSDDT(k=4,df=30,corr=0.6) #based on the critical values, we reject H2, H1, H3 in a sequence and accept H4. ```

### Example output

```Loading required package: mvtnorm
c1    c2    c3    c4
1.697 1.970 2.118 2.217
```

DunnettTests documentation built on May 2, 2019, 9:13 a.m.