Re: [R] Type II and III sum of square in Anova (R, car package)

From: Prof Brian Ripley <>
Date: Sun 27 Aug 2006 - 17:37:01 EST

I think this starts from the position of a batch-oriented package. In R you can refit models with update(), add1() and drop1(), and experienced S/R users almost never use ANOVA tables for unbalanced designs. Rather than fit a pre-specified set of sub-models, why not fit those sub-models that appear to make some sense for your problem and data?

SInce your post lacks a signature and your credentials we have no idea of your background, which makes it very difficult even to know what reading to suggest to you. But Bill Venables' 'exegeses' paper ( may be a good start. It does explain your comment '3.'.

On Sun, 27 Aug 2006, Amasco Miralisus wrote:

> Hello everybody,
> I have some questions on ANOVA in general and on ANOVA in R particularly.
> I am not Statistician, therefore I would be very appreciated if you answer
> it in a simple way.
> 1. First of all, more general question. Standard anova() function for lm()
> or aov() models in R implements Type I sum of squares (sequential), which
> is not well suited for unbalanced ANOVA. Therefore it is better to use
> Anova() function from car package, which was programmed by John Fox to use
> Type II and Type III sum of squares. Did I get the point?
> 2. Now more specific question. Type II sum of squares is not well suited
> for unbalanced ANOVA designs too (as stated in STATISTICA help), therefore
> the general rule of thumb is to use Anova() function using Type II SS
> only for balanced ANOVA and Anova() function using Type III SS for
> unbalanced ANOVA? Is this correct interpretation?
> 3. I have found a post from John Fox in which he wrote that Type III SS
> could be misleading in case someone use some contrasts. What is this about?
> Could you please advice, when it is appropriate to use Type II and when
> Type III SS? I do not use contrasts for comparisons, just general ANOVA
> with subsequent Tukey post-hoc comparisons.
> Thank you in advance,
> Amasco
> [[alternative HTML version deleted]]
> ______________________________________________
> mailing list
> PLEASE do read the posting guide
> and provide commented, minimal, self-contained, reproducible code.

Brian D. Ripley,        
Professor of Applied Statistics,
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

______________________________________________ mailing list
PLEASE do read the posting guide
and provide commented, minimal, self-contained, reproducible code.
Received on Sun Aug 27 17:49:13 2006

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.1.8, at Mon 28 Aug 2006 - 00:22:40 EST.

Mailing list information is available at Please read the posting guide before posting to the list.