From: <Arne.Muller_at_sanofi-aventis.com>

Date: Sat 27 Aug 2005 - 00:57:02 EST

R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Aug 27 02:08:07 2005

Date: Sat 27 Aug 2005 - 00:57:02 EST

Hello,

I'm posting this to receive some comments/hints about a rather statistical than R-technical question ... .

In an anova of a lme factor SSPos11 shows up non-significant, but in the t-test of the summay 2 of the 4 levels (one for constrast) are significant. See below for some truncated output.

I realize that the two test are different (F-test/t-test), but I'm looking for for a "meaning". Maye you have a schenario that explains how these differences can be created and how you'd go ahead and analyse it further.

When I use SSPos11 as te only fixed effect, it does it is not significant in either anova nor t-test, and a boxplot of the factor shows that the levels are all quite similar (similar variance and mean). Might the effect I observe be linked to an unbalance design in the multifactorial model?

thanks a lot for your help, +kind regards, Arne...

> anova(fit)

numDF denDF F-value p-value (Intercept) 1 540 323.4442 <.0001 SSPos1 3 540 15.1206 <.0001 ... SSPos11 3 540 1.1902 0.3128

> summary(fit)

Linear mixed-effects model fit by REML

Data: d.orig

AIC BIC logLik

1007.066 1153.168 -469.5329

Random effects:

Formula: ~1 | Method

(Intercept) Residual

StdDev: 0.4000478 0.4943817

Fixed effects: log(value + 7.5) ~ SSPos1 + SSPos2 + SSPos6 + SSPos7 + SSPos10 + SSPos11 + SSPos13 + SSPos14 + SSPos18 + SSPos19 + Value Std.Error DF t-value p-value (Intercept) 2.8621811 0.23125065 540 12.376964 0.0000 SSPos1C -0.1647937 0.06293993 540 -2.618269 0.0091 SSPos1G -0.3448095 0.05922479 540 -5.822047 0.0000 SSPos1T 0.1083988 0.06087095 540 1.780797 0.0755 ... SSPos11C -0.1540292 0.06171635 540 -2.495761 0.0129 SSPos11G -0.1428980 0.05993122 540 -2.384368 0.0175 SSPos11T -0.0039434 0.06133920 540 -0.064289 0.9488...

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R-help@stat.math.ethz.ch mailing list

https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Sat Aug 27 02:08:07 2005

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