# SNK.test: Student-Newman-Keuls (SNK) In agricolae: Statistical Procedures for Agricultural Research

## Description

SNK is derived from Tukey, but it is less conservative (finds more differences). Tukey controls the error for all comparisons, where SNK only controls for comparisons under consideration. The level by alpha default is 0.05.

## Usage

 `1` ```SNK.test(y, trt, DFerror, MSerror, alpha = 0.05, group=TRUE, main = NULL,console=FALSE) ```

## Arguments

 `y` model(aov or lm) or answer of the experimental unit `trt` Constant( only y=model) or vector treatment applied to each experimental unit `DFerror` Degree free `MSerror` Mean Square Error `alpha` Significant level `group` TRUE or FALSE `main` Title `console` logical, print output

## Details

It is necessary first makes a analysis of variance.

## Value

 `statistics` Statistics of the model `parameters` Design parameters `snk` Critical Range Table `means` Statistical summary of the study variable `comparison` Comparison between treatments `groups` Formation of treatment groups

## Author(s)

Felipe de Mendiburu

## References

1. Principles and procedures of statistics a biometrical approach Steel & Torry & Dickey. Third Edition 1997
2. Multiple comparisons theory and methods. Departament of statistics the Ohio State University. USA, 1996. Jason C. Hsu. Chapman Hall/CRC.

`BIB.test`, `DAU.test`, `duncan.test`, `durbin.test`, `friedman`, `HSD.test`, `kruskal`, `LSD.test`, `Median.test`, `PBIB.test`, `REGW.test`, `scheffe.test`, `waerden.test`, `waller.test`, `plot.group`

## Examples

 ``` 1 2 3 4 5 6 7 8 9 10 11``` ```library(agricolae) data(sweetpotato) model<-aov(yield~virus,data=sweetpotato) out <- SNK.test(model,"virus", console=TRUE, main="Yield of sweetpotato. Dealt with different virus") print(SNK.test(model,"virus", group=FALSE)) # version old SNK.test() df<-df.residual(model) MSerror<-deviance(model)/df out <- with(sweetpotato,SNK.test(yield,virus,df,MSerror, group=TRUE)) print(out\$groups) ```

### Example output

```Study: Yield of sweetpotato. Dealt with different virus

Student Newman Keuls Test
for yield

Mean Square Error:  22.48917

virus,  means

yield      std r  Min  Max
cc 24.40000 3.609709 3 21.7 28.5
fc 12.86667 2.159475 3 10.6 14.9
ff 36.33333 7.333030 3 28.0 41.8
oo 36.90000 4.300000 3 32.1 40.4

alpha: 0.05 ; Df Error: 8

Critical Range
2         3         4
8.928965 11.064170 12.399670

Means with the same letter are not significantly different.

Groups, Treatments and means
a 	 oo 	 36.9
a 	 ff 	 36.33
b 	 cc 	 24.4
c 	 fc 	 12.87
\$statistics
Mean      CV  MSerror
27.625 17.1666 22.48917

\$parameters
Df ntr alpha test name.t
8   4  0.05  SNK  virus

\$SNK
Table CriticalRange
2 3.261182      8.928965
3 4.041036     11.064170
4 4.528810     12.399670

\$means
yield      std r  Min  Max
cc 24.40000 3.609709 3 21.7 28.5
fc 12.86667 2.159475 3 10.6 14.9
ff 36.33333 7.333030 3 28.0 41.8
oo 36.90000 4.300000 3 32.1 40.4

\$comparison
Difference pvalue sig.        LCL        UCL
cc-fc  11.5333333 0.0176    *   2.604368  20.462299
cc-ff -11.9333333 0.0151    * -20.862299  -3.004368
cc-oo -12.5000000 0.0291    * -23.564170  -1.435830
fc-ff -23.4666667 0.0008  *** -34.530836 -12.402497
fc-oo -24.0333333 0.0012   ** -36.433003 -11.633664
ff-oo  -0.5666667 0.8873       -9.495632   8.362299

\$groups
NULL

trt    means M
1  oo 36.90000 a
2  ff 36.33333 a
3  cc 24.40000 b
4  fc 12.86667 c
```

agricolae documentation built on Sept. 13, 2017, 1:03 a.m.