[R] interpreting an LME regression result...
Johan Jackson
johan.h.jackson at gmail.com
Sat Nov 10 08:58:21 CET 2007
Any help would be most appreciated. (Don't make me get down on my
hands and knees and beg for help, cause I'll do it!!) My boss has me
learning R and doing nested regression with the report due Mon (Friday
night statistics...fun. ). Anyway, here's my problem:
In a regression equation not accounting for the fact that people are
nested in families, the result for Z variable is VERY strong (beta =
-4511), but this result is much weaker when I use lme and account for
people nested in families (beta = -2613). I'm struggling with a verbal
interpretation of this result. Is it because the effect of Z within
families is not very strong, but between family variation is high?
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If my R syntax would be helpful, it's below:
BIG EFFECT OF Z (using lm)
summary(lm(Y ~ X + Z + age ,data=pharma.data ,na.action='na.omit'))
Estimate Std. Error t value Pr(>|t|)
(Intercept) 102.27 24.98 4.09 7e-05 ***
X -629.76 267.87 -2.35 0.020 *
Z -4511.96 2032.39 -2.22 0.028 *
age 1.88 1.42 1.32 0.188
SMALLER EFFECT OF Z (using lme)
summary(lme(Y ~ X + Z + age, random = ~1|Family.ID,
data=pharma.data, method="ML", na.action='na.omit'))
Value Std.Error DF t-value p-value
(Intercept) 103.9 20.0 85 5.200 0.0000
X. -417.3 179.3 85 -2.327 0.0223
Z -2613.0 1845.1 85 -1.416 0.1604
age 1.3 1.2 85 1.126 0.2632
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