Hello,
I work with the kruskla function of the agricolae package to conduct
Kurskal-Wallis tests.
The kurskal function has the argument "group"=T/F.
If group=T, the output of the kruskal test assigns a "significance letter" to
each mean of each tested treatment (means with the same letter are not
significantly different).
However, if I compare the "significance letters" with the p-values (obtained if
group=F) sometimes the sign. letters and p-values do not coincide.
E.g. in my example the treatments "2" and "2C" differ significantly from each
other (p.value=0.0332, level of significance=0.05) , however both of them are
assigned the letter "a" if group=T is used.
Does anyone know why that's the case? First I thought is because I use a holm
correction, but this should already be seen in the actual p-values.
The problem is that I would like to use the "sign. letters" in one of my
figures (so the reader can easily distinguish which treatments are different
from each other) but also use the p-values in the text (and of course sometimes
the letters and p-values do not coincide)
Thank you Mike
EXAMPLE:
#Below is the code and the dput of my data frame (called "example")
kruskal(example$H.polone,example$Position, p.adj = 'holm', console = T, group =
F)
#group=F shows p-values, group=T shows sign. letters
> dput(example)
structure(list(leaf = structure(c(2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L,
2L, 2L, 2L, 2L), .Label = c("Cot", "L1", "L2", "L4", "L7"), class = "factor"),
H.polone = c(980.310618, 2474.133482, 4406.901817, 2233.141989,
1284.855658, 1202.881507, 2393.532397, 2639.775244, 2853.759572,
3009.791049, 2734.731629, 1539.309599, 9634.265878, 15627.14214,
13212.8464, 4.679175916, 5004.820592, 17045.7964, 17461.49723,
14065.03002, 24452.43564, 17267.91494, 9483.597645, 535.05702,
582.0554615, 163.9588478, 527.1015784, 621.3924963, 519.8953943,
1429.334963, 584.2620172, 600.5646899, 568.2045799, 583.0237882,
1054.557537, 576.5345625, 366.6277524, 644.2932199, 877.2948815,
343.9021574, 960.3431623, 899.6237855, 834.5025197), Position =
structure(c(6L,
6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 5L, 5L, 5L, 5L,
5L, 5L, 5L, 5L, 5L, 5L, 5L, 8L, 8L, 8L, 8L, 8L, 8L, 8L, 8L,
8L, 8L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L, 7L), .Label = c("1",
"1C", "1L4", "1L4C", "2", "2C", "2L4", "2L4C", "3", "3C",
"3L4", "3L4C", "4L4", "4L4C", "5L4", "5L4C"), class = "factor")), class =
"data.frame", row.names = c(NA,
-43L), .Names = c("leaf", "H.polone", "Position"))
Eisenring Michael, Msc.
PhD Student
Federal Department of Economic Affairs, Education and Research
EAER
Institute of Sustainability Sciences ISS
Biosafety
Reckenholzstrasse 191, CH-8046 Z�rich
Tel. +41 44 37 77181
Fax +41 44 37 77201
michael.eisenr...@agroscope.admin.ch<mailto:michael.eisenr...@agroscope.admin.ch>
www.agroscope.ch<http://www.agroscope.ch/>
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