Re: [R] Comparing two groups of proportions

From: Rolf Turner <r.turner_at_auckland.ac.nz>
Date: Wed, 11 Jun 2008 08:05:57 +1200

On 10/06/2008, at 6:08 PM, Ivan Adzhubey wrote:

> 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.

	As far as I can see there is no way of doing anything sensible unless
	you know or obtain the item by item results.  There's not much you
	can do (sensibly) with the summaries provided in your original posting.

>
>> 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).
	It still seems to me that the relevant questions, no matter how you
	slice the situation, have to be expressed in terms of conditional
	probabilities rather than the marginals.  I.e. what's the probability
	the procedure 2 passes an item given that procedure 1 has passed it?
	What's the probability given that procedure 1 has failed it?

		cheers,

			Rolf Turner

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