williamsTest: Performs Williams Test

In StatCharrms: Statistical Analysis of Chemistry, Histopathology, and Reproduction Endpoints Including Repeated Measures and Multi-Generation Studies

Description

The Williams test is a parametric test for trend. It is used to test for a trend when normality assumption is met.

Usage

	williamsTest(df,resp,trt,direction='decreasing',SeIn=NULL)

Arguments

df	A data set.
resp	The name (as a string) of the response variable.
trt	The name (as a string) of the treatment variable.
direction	The direction of the test statistic which can either be 'increasing', 'decreasing').
SeIn	This is used to specify a different standard error then the one calculated within the WilliamsTest function.

Value

trt	The treatment level the test statistic corresponds to.
Y.Tilde	The amalgamated averages for the treatment level.
Se Diff	The standard error.
DF	The degrees of freedom.
Will	The value of the Williams test statistic.
TCrit	The critical value of the Williams test statistic, corresponding to a p-value of 0.05.

Author(s)

Joe Swintek

References

Williams D.A. (1971). A test for differences between treatment means when several dose levels are compared with a zero dose control. Biometrics 27(1):103-117.
Green J., Springer T., Holbeck H. Statistical Analysis of Ecotoxicology Data (Wiley in press)

Examples

	#Data 
		data(lengthWeightData)
	#Subset the data
		SubData<-lengthWeightData[lengthWeightData$Age=='16 week', ] 
		SubData<-SubData[SubData$Generation=='F1', ]
		SubData<-SubData[SubData$SEX=='M', ]
		williamsTest(df=SubData, trt='Treatment', 
			resp='WEIGHT', direction='decreasing',SeIn=NULL)
		

Example output

R session is headless; GTK+ not initialized.

(R:11398): Gtk-WARNING **: 13:43:09.192: gtk_disable_setlocale() must be called before gtk_init()
R session is headless; GTK+ not initialized.
Type Run.StatCharrms() to begin.
   Treatment Y.Tilde    Y0 Se.Diff DF    Will TCrit Signif
Q5         6   374.6 357.5   70.74 28 -0.2415 1.826      .
Q4         5   374.6 357.5   74.19 28 -0.2302 1.811      .
Q3         4   374.6 357.5   74.19 28 -0.2302 1.799      .
Q2         3   374.6 357.5   70.74 28 -0.2415 1.780      .
           2   374.6 357.5   70.74 28 -0.2415 1.701      .

StatCharrms documentation built on Nov. 14, 2020, 5:09 p.m.