RE: [R] Testing autocorrelation & heteroskedasticity of residuals in ts

From: Wayne Jones <JonesW_at_kssg.com>
Date: Wed 21 Jul 2004 - 18:41:07 EST


Hi Vito,
I would treat the residuals as a time series. You can fit an arima model to the residuals. For example:

data(nottem)
temp<-stl(nottem, "per")
my.arima<-arima(temp$time.series[,3], order=c(1,0,0), include.mean = FALSE) my.arima
tsdiag(my.arima)

If the ar1 term is significant then the residuals are auto-correlated. The DW statistic is just another test for this. The command tsdiag gives diagnostic plots for the arima model fit.

In terms of heteroskedasticity, the Bruce-Pagan test from package lmtest tests for variance changing as a function of another variable. I think (although I am less sure) you can still use the test.

To test whether your variance of residuals is monotonically increasing (or maybe decreasing) over time I would use:

library(lmtest)
Y<- as.numeric(temp$time.series[,3])
X<-1:nrow(temp$time.series)
bptest(Y~X)

Regards

Wayne

-----Original Message-----
From: Vito Ricci [mailto:vito_ricci@yahoo.com]
Sent: 21 July 2004 08:35
To: r-help@stat.math.ethz.ch
Subject: [R] Testing autocorrelation & heteroskedasticity of residuals in ts

Hi,

I'm dealing with time series. I usually use stl() to estimate trend, stagionality and residuals. I test for normality of residuals using shapiro.test(), but I can't test for autocorrelation and heteroskedasticity. Is there a way to perform Durbin-Watson test and Breusch-Pagan test (or other simalar tests) for time series?
I find dwtest() and bptest() in the package lmtest, but it requieres an lm object, while I've a ts object. Any help will be appreciated.
Best
Vito



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https://www.stat.math.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html Received on Wed Jul 21 18:55:37 2004

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