Dear R users:
I have a simple lme model based on the following data:
sub ? ? trial ? angle ? RMSy
1 ? ? ? 1 ? ? ? 30 ? ? ?3.745084
1 ? ? ? 2 ? ? ? 0 ? ? ? 7.520667
1 ? ? ? 3 ? ? ? 90 ? ? ?11.17038
1 ? ? ? 4 ? ? ? 15 ? ? ?7.581526
1 ? ? ? 5 ? ? ? 60 ? ? ?11.17822
1 ? ? ? 6 ? ? ? 75 ? ? ?8.440891
1 ? ? ? 7 ? ? ? 45 ? ? ?13.19024
1 ? ? ? 8 ? ? ? 15 ? ? ?9.822035
1 ? ? ? 9 ? ? ? 60 ? ? ?6.002665
1 ? ? ? 10 ? ? ?75 ? ? ?4.393961
1 ? ? ? 11 ? ? ?0 ? ? ? 7.436676
When I run the model the results show that 0vs45, 0vs60, 0vs75, and 0vs90 are all significant main effects:
m.base01<-lme(RMSy ~ angle+trial, data=data, ?random=~ trial|sub,method='ML')
summary(m.base01)
Fixed effects: RMSy ~ angle + trial
? ? ? ? ? ? ? ? ? ? ? ?Value ? Std.Error ? ? ? DF ? ? t-value ? ? p-value
(Intercept) ?5.236020 ? 0.6312637 ? ? ? 267 8.294505 ?0.0000
angle15 ? ? -0.687669 ? 0.4140277 ? ? ? 267 -1.660925 ?0.0979
angle30 ? ? -0.571092 ? 0.4129365 ? ? ? 267 -1.383001 ?0.1678
angle45 ? ? -0.984597 ? 0.4139330 ? ? ? 267 -2.378638 ?0.0181
angle60 ? ? -0.874718 ? 0.4135615 ? ? ? 267 -2.115085 ?0.0353
angle75 ? ? -1.389835 ? 0.4113411 ? ? ? 267 -3.378788 ?0.0008
angle90 ? ? -1.620493 ? 0.4133209 ? ? ? 267 -3.920666 ?0.0001
trial ? ? ? -0.009372 ? 0.0299782 ? ? ? 267 -0.312620 ?0.7548
However, when I try to run a Tukey posthoc test, I get different results (notice that the estimates are the same as the main effect values above): ONLY 0vs90 is significant at p<.05 :
summary(glht(m.base01, linfct=mcp(angle = "Tukey")))
? ? ? ? Simultaneous Tests for General Linear Hypotheses
Multiple Comparisons of Means: Tukey Contrasts
Fit: lme.formula(fixed = RMSy ~ angle + trial, data = data, random = ~trial |
? ?sub, method = "ML")
Linear Hypotheses:
? ? ? ? ? ? Estimate Std. Error z value Pr(>|z|)
15 - 0 == 0 ? -0.6877 ? ? 0.4082 ?-1.684 ?0.62652
30 - 0 == 0 ? -0.5711 ? ? 0.4072 ?-1.403 ?0.80077
45 - 0 == 0 ? -0.9846 ? ? 0.4081 ?-2.412 ?0.19329
60 - 0 == 0 ? -0.8747 ? ? 0.4078 ?-2.145 ?0.32592
75 - 0 == 0 ? -1.3898 ? ? 0.4056 ?-3.427 ?0.01070 *
90 - 0 == 0 ? -1.6205 ? ? 0.4075 ?-3.976 ?0.00138 **
30 - 15 == 0 ? 0.1166 ? ? 0.4079 ? 0.286 ?0.99996
45 - 15 == 0 ?-0.2969 ? ? 0.4078 ?-0.728 ?0.99090
60 - 15 == 0 ?-0.1870 ? ? 0.4078 ?-0.459 ?0.99931
75 - 15 == 0 ?-0.7022 ? ? 0.4050 ?-1.734 ?0.59342
90 - 15 == 0 ?-0.9328 ? ? 0.4073 ?-2.290 ?0.24842
45 - 30 == 0 ?-0.4135 ? ? 0.4082 ?-1.013 ?0.95124
60 - 30 == 0 ?-0.3036 ? ? 0.4074 ?-0.745 ?0.98971
75 - 30 == 0 ?-0.8187 ? ? 0.4052 ?-2.021 ?0.40123
90 - 30 == 0 ?-1.0494 ? ? 0.4076 ?-2.574 ?0.13377
60 - 45 == 0 ? 0.1099 ? ? 0.4077 ? 0.269 ?0.99997
75 - 45 == 0 ?-0.4052 ? ? 0.4059 ?-0.998 ?0.95449
90 - 45 == 0 ?-0.6359 ? ? 0.4078 ?-1.559 ?0.70835
75 - 60 == 0 ?-0.5151 ? ? 0.4050 ?-1.272 ?0.86496
90 - 60 == 0 ?-0.7458 ? ? 0.4074 ?-1.831 ?0.52730
90 - 75 == 0 ?-0.2307 ? ? 0.4049 ?-0.570 ?0.99763
Why does the Tukey not match the lme results?
Any help would be much appreciated!
Thanks, Alen
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Alen Hajnal, PhD.
Department of Psychology
The University of Southern Mississippi
118 College Drive #5025
Hattiesburg, MS 39406
USA
Tel. +1 (601) 266-4617
alen.hajnal @ usm.edu
http://ocean.otr.usm.edu/~w785427/lab.html