Dear All,
I am trying to put some Confidence intervals on some regressions from a linear
model with no luck. I can extract the fitted values using 'predict', but am
having difficulty in getting at the confidence intervals, or the standard
errors.
Any suggestions would be welcome
Cheers
Guy
Using Version 2.1.0 (2005-04-18) on a PC
vol.mod3 <- lm(log.volume~log.area*lake,data=vol)
summary(vol.mod3)
plot(c(1.3,2.5),c(-0.7,0.45),type="n",xlab="Log area",ylab="Log volume")
areapred.a <- seq(min(vol$log.area[vol$lake=="a"]),
max(vol$log.area[vol$lake=="a"]), length=100)
areapred.b <- seq(min(vol$log.area[vol$lake=="b"]),
max(vol$log.area[vol$lake=="b"]), length=100)
preda <- predict(vol.mod3, data.frame(log.area=areapred.a,interval="confidence"
,lake=rep("a",100)))
#This gives the fitted values as predicted, but no CIs
> preda
1 2 3 4 5 6
7 8 9
-0.562577529 -0.553263576 -0.543949624 -0.534635671 -0.525321718 -0.516007765
-0.506693813 -0.497379860 -0.488065907
10 11 12 13 14 15
16 17 18
-0.478751955 -0.469438002 -0.460124049 -0.450810097 -0.441496144 -0.432182191
-0.422868239 -0.413554286 -0.404240333
19 20 21 22 23 24
25 26 27
-0.394926380 -0.385612428 -0.376298475 ETC ETC
#As does this, but with no SEs
> preda <- predict(vol.mod3, data.frame(log.area=areapred.a,se.fit=T
> ,lake=rep("a",100)))
> preda
1 2 3 4 5 6
7 8 9 10
-0.562577529 -0.553263576 -0.543949624 -0.534635671 -0.525321718 -0.516007765
-0.506693813 -0.497379860 -0.488065907 -0.478751955
11 12 13 14 15 16
17 18 19 20
-0.469438002 -0.460124049 -0.450810097 ETC ETC
--------------------------------------------------------
Guy J Forrester
Biometrician
Manaaki Whenua - Landcare Research
PO Box 69, Lincoln, New Zealand.
Tel. +64 3 325 6701 x3738
Fax +64 3 325 2418
E-mail [EMAIL PROTECTED]
www.LandcareResearch.co.nz
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