[R] Comparing two groups of proportions

Yvonnick NOEL yvonnick.noel at uhb.fr
Wed Jun 11 09:28:49 CEST 2008

Hi Ivan,

It was not clear from your original post that QA was a repeated factor.

But your problem may be reframed very much like you would do with a 
McNemar chi-square: Just count the number of times both procedure give 
the same result, of each kind, and different results, again of both 
kinds, to get four counts by condition. These events are probably 
independent within your setting.

You should then be able to test various binomial or Poisson models with 
the proper equality constraints.


Yvonnick Noel, PhD
University of Brittany at Rennes
> Re: [R] Comparing two groups of proportions
> To: r-help at r-project.org
> Message-ID: <200806100208.51742.iadzhubey at rics.bwh.harvard.edu>
> Content-Type: text/plain; charset=iso-8859-1
> Hi Rolf,
> On Monday 09 June 2008 11:16:57 pm Rolf Turner wrote:
>> > Your approach tacitly assumes --- as did the poster's question --- that
>> > the probability of passing an item by one method is *independent* of
>> > whether it is passed by the other method.  Which makes the methods
>> > effectively independent of the nature of the item being assessed!
> So it seems I can't just block my primary factor (QA procedure) by nuisance 
> one (production line) and run Cochran test to see if effects of primary 
> factor are identical for both its levels.
>> > Not much actual quality being assured there!
> In fact, I am not interested in quality of QA procedures as much as in how 
> different the results are (error component).
> Thanks,
> Ivan

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