At 09:12 AM 11/19/2003 -0500, Nirmal Govind wrote:
Thank you very much John and Sundar for your quick responses.
From your description, it's not possible to tell what you did or exactly what happened -- either in R or in Minitab (and JMP).
John: in R, I fit the model using lm exactly as you did.. however, for the ANOVA table, I used summary(lm) and also tried aov(lm) but not anova(lm) ... and it looks like therein lies the problem.. the output of these differ.
What's the difference between aov, summary and anova? And when should one use one as opposed to the other? It's hard to tell from the help for these functions...
Briefly, as ?aov mentions, aov() calls lm() -- the difference is in the results produced by generic functions like summary(), print(), etc. For example, summary.lm() produces a table of coefficients, std. errors, etc., while summary.aov() produces an ANOVA table. One would not normally call aov() with a linear-model object as an argument (though this works). Applied to a linear-model object, summary() produces coefficients, etc. (as mentioned), while anova() produces a (sequential) ANOVA table. This seems apparent to me from the output.
More generally, it probably makes sense to read introductory material about R -- such as the introductory manual that comes with the software or one of several books (some freely available on the Internet) that describe its use (see under documentation at <http://www.r-project.org/>).
John
----------------------------------------------------- John Fox Department of Sociology McMaster University Hamilton, Ontario, Canada L8S 4M4 email: [EMAIL PROTECTED] phone: 905-525-9140x23604 web: www.socsci.mcmaster.ca/jfox
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