Calculates equivalent deviates for Dunnett’s simultaneous confidence interval around a control (R.W. Payne).
Options
METHOD = string token |
Form of the alternative hypothesis (twosided, greaterthan, lessthan); default twos |
|---|---|
NTREATMENTS = scalar |
Number of treatments being compared |
DF = scalar |
Number of residual degrees of freedom |
REPTREATMENTS = scalar or variate |
Specifies the replication of the treatments |
REPCONTROL = scalar |
Specifies the replication of the control |
TOLERANCE = scalar |
Tolerance for the difference between the probability for the calculated equivalent deviate and that requested by CIPROBABILITY; default 0.0001 |
Parameters
CIPROBABILITY = scalars |
Specifies the probability for the confidence interval |
|---|---|
ED = scalars |
Saves the equivalent deviate |
Description
Dunnett’s test is useful when you want to compare several treatments with a control treatment, and use a critical value that controls the chance that any one comparison may be found significant when there are no true differences. (It is designed thus to take account of the fact that you are making multiple comparisons with the control.) The test can be preformed in Genstat using the AMDUNNETT procedure, and this uses EDDUNNETT to calculate the critical value (i.e. the equivalent deviate of the probability distribution).
The METHOD option defines the type of interval that is formed. By default EDDUNNETT assumes a two-sided interval. If you set METHOD=lowerthan, it assumes a lower confidence interval, assessing the one-sided test of the null hypothesis that the treatment means are not lower than the control mean. Alternatively, you can set METHOD=greaterthan, to assume an upper confidence interval, assessing the one-sided test of the null hypothesis that the treatment means are not greater than the mean of the control.
The NTREATMENTS option specifies the number of treatments that are being compared with the control. The REPTREATMENTS option specifies their replication, in a scalar if they all have the same replication, or in a variate if their replications differ. The REPCONTROL option specifies the replication of the control, and the DF option specifies the number of residual degrees of freedom.
The probability for the confidence interval is specified by the CIPROBABILITY parameter, and the ED parameter saves the equivalent deviate.
The equivalent deviate is estimated by an iterative process. The TOLERANCE option controls the accuracy of the estimation, defining the how close the probability corresponding to the calculated equivalent deviate must be to that requested by CIPROBABILITY; default 0.0001
Options: METHOD, NTREATMENTS, DF, REPTREATMENTS, REPCONTROL, TOLERANCE.
Parameters: CIPROBABILITY, ED.
See also
Procedure: AMDUNNETT.
Example
CAPTION 'EDDUNNETT examples'; STYLE=meta
EDDUNNETT [NTREATMENTS=3; DF=8] 0.95; critical
PRINT critical
EDDUNNETT [METHOD=greaterthan; NTREATMENTS=3; DF=8] 0.95; critical
PRINT critical
VARIATE [VALUES=3,2,3] trep
EDDUNNETT [NTREATMENTS=3; DF=8; REPCONTROL=2; REPTREATMENTS=trep]\
0.95; critical
PRINT critical
EDDUNNETT [METHOD=greaterthan; NTREATMENTS=3; DF=8; REPCONTROL=2;\
REPTREATMENTS=trep] 0.95; critical
PRINT critical
EDDUNNETT [METHOD=lessthan; NTREATMENTS=3; DF=8; REPCONTROL=2;\
REPTREATMENTS=trep] 0.95; critical
PRINT critical