# [R] zigzag confidence interval in a plot

Fri May 17 17:28:50 CEST 2013

```Hello,

Try the following.

lmR <- lm(cd\$Depth ~ cd\$CHAOsep12RNA)
pconfR <- predict(lmR,interval="confidence")
pcR <- pconfR[order(pconfR[, 1]), ]  # Add this line

plot(cd\$CHAOsep12RNA,cd\$Depth, ylim = rev(range(0:100)), xlab="CHAO",
ylab="Depth", pch=15, las=2, main="Sep12-RNA", cex.main=1)
abline(lmR)
matlines(sort(cd\$CHAOsep12RNA), pcR[,c("lwr", "upr")], col=1, lty=2) #
changed

Hope this helps,

Em 17-05-2013 14:03, Ozgul Inceoglu escreveu:
> Dear All,
>
> When I plot the values and linear regression line for one data set, it is fine. But for another one I see zigzags, when I plot the confidence interval
>
>> cd
> Depth	CHAOsep12RNA
> 9,94	804
> 25,06	1476,833333
> 40,04	1540,561404
> 50,11	1575,166667
> 52,46	349,222222
> 54,92	1941,5
> 57,29	1053,507042
> 60,11	1535,1
> 70,04	2244,963303
> 79,97	1954,507042
> 100,31	2679,140625
>
>
>> plot(cd\$CHAOsep12RNA,cd\$Depth, ylim = rev(range(0:100)), xlab="CHAO", ylab="Depth", pch=15, las=2, main="Sep12-RNA", cex.main=1)
>> lmR <- lm(cd\$Depth~cd\$CHAOsep12RNA)
>> abline(lmR)
> pconfR <- predict(lmR,interval="confidence")
> matlines(cd\$CHAOsep12RNA,pconfR[,c("lwr","upr")], col=1, lty=2)
>
> I also tried
>
>> newx <- seq(min(cd\$CHAOsep12RNA), max(cd\$CHAOsep12RNA), length.out=11)
>> a <- predict(lmR, newdata=data.frame(CHAO=newx), interval=c("confidence"))
>> plot(cd\$CHAOsep12RNA,cd\$Depth, ylim = rev(range(0:100)), xlab="CHAO", ylab="Depth", pch=15, las=2, main="Sep12-RNA", cex.main=1)
>> abline(lmR)
>> lines(cd\$CHAOsep12RNA, a[,2], lty=2)
>
> But I see both cases kind of zigzags. What can it be the reason? thank you!
>
>
>
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