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Error in ANOVA for model comparison

2 messages · Rosario Garcia Gil, John Fox

Rosario Garcia Gil
# 
Hello

I am trying to compare two models using anova(), however I get a message error (see below).
In the net I only found some information on certain library(car) for which one should use anova with A capital letter (Anova instead of anova), but I could not find car library as it says it does not exist.
Error in anova.lmlist(object, ...) : 
  models were not all fitted to the same size of dataset

I have NA in the datafile, should that be the problem?

Kind regards and thanks in advance
Rosario
John Fox
# 
Dear Rosario,

Because of missing data in the additional variable PHt, the two models
weren't fit to the same subset of valid observations -- the default in lm()
is to use complete cases for the variables in the model. 

A mechanical solution is to use na.omit() to filter your data set, only for
the variables you intend to use, to produce a data set with no NAs. Then
you'll fit each model to a consistent subset of valid cases. 

Of course, if you have a substantial amount of missing data, complete-case
analysis is probably a poor strategy.

I hope this helps,
 John

--------------------------------
John Fox
Senator William McMaster
  Professor of Social Statistics
Department of Sociology
McMaster University
Hamilton, Ontario, Canada
http://socserv.mcmaster.ca/jfox