Using multcomp in post-hoc comparisons
Iker Vaquero Alba <karraspito at yahoo.es> wrote:
I was just wondering about the degrees of freedom of those z
scores. The z scores are compared with a standard normal distribution. So there are no degrees of freedom to report. For the rest of message, although your model does have mixed effects, the questions are not specifically related to mixed models, but to the interpreation of Tukey's test, so I recommend you to ask it in a more general purpose list or forum. Regards, Helios
Dear list: I am using "multcomp" package to make post-hoc comparisons in a
7-level
factor. The analysis performed is at follows:
minclutchmodel2<-lmer(clsize2~mod+inslargest+briventralst+inslargest:briventra
lst+(1|site/pair)+(1|year),family=poisson)
cht<-glht(minclutchmodel2,linfct=mcp(mod="Tukey")) summary(cht, test = univariate())
Simultaneous Tests for General Linear Hypotheses
Multiple Comparisons of Means: Tukey Contrasts
Fit: glmer(formula = clsize2 ~ mod + inslargest + briventralst +
inslargest:briventralst +
(1 | site/pair) + (1 | year), family = poisson)
Linear Hypotheses:
Estimate Std. Error z value Pr(>|z|)
EC - E == 0 -0.5654710 0.5710626 -0.990 0.322072
R - E == 0 -0.2080028 0.3590288 -0.579 0.562354
RC - E == 0 -0.9835988 0.4836405 -2.034 0.041978 *
S - E == 0 -1.3622236 0.3916350 -3.478 0.000505 ***
SC - E == 0 -0.0009705 0.4017037 -0.002 0.998072
U - E == 0 -0.1578700 0.2907425 -0.543 0.587137
R - EC == 0 0.3574681 0.5494919 0.651 0.515341
RC - EC == 0 -0.4181278 0.6527767 -0.641 0.521823
S - EC == 0 -0.7967526 0.5570890 -1.430 0.152658
SC - EC == 0 0.5645005 0.6019210 0.938 0.348331
U - EC == 0 0.4076009 0.5309090 0.768 0.442641
RC - R == 0 -0.7755959 0.4543557 -1.707 0.087818 .
S - R == 0 -1.1542208 0.3641393 -3.170 0.001526 **
SC - R == 0 0.2070323 0.3462441 0.598 0.549882
U - R == 0 0.0501328 0.2431495 0.206 0.836650
S - RC == 0 -0.3786249 0.4875128 -0.777 0.437368
SC - RC == 0 0.9826283 0.4792105 2.051 0.040314 *
U - RC == 0 0.8257287 0.4180611 1.975 0.048252 *
SC - S == 0 1.3612531 0.4079427 3.337 0.000847 ***
U - S == 0 1.2043536 0.3058414 3.938 8.22e-05 ***
U - SC == 0 -0.1568995 0.2964628 -0.529 0.596640
---
Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.?
0.1 ? ? 1
(Univariate p values reported) I was just wondering about the degrees of freedom of those z
scores. As
they're pairwise comparisons, I guess it's comparing the means of the
2
levels involved for each caso, so I would say the degrees of freedom
for each
should be 1. Am I right or is there something that I'm missing? Also, if I want to know the direction of the effect of the factor,
I
mean, which are the levels that are contributing more to the
significant
effect of the factor on the model, according to these data, would I
say it's
S>RC (both levels are significant, but S to a greater extent than
RC)?
Thank you very much.