Talk:Price equation

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[edit] Comments on the Rewrite

Whow. This page has suddenly changed a lot. I like a lot of the new contents of this page as it suddenly adds to the understanding of Price's equation, however, I think it has lost a lot of its encyclopedic value since the huge edit by PAR on 23 Nov 2004. A couple of reasons for this comment are:

• The Price equation itself (not the small one, but the full one) doesn't appear in the article until somewhere half way through the article, after some examples have already been given. A better structure would be to give the Price equation, then give its variations (and derivation), and then (maybe even in a seperate page, like Price equation (examples)) give some examples
• The article is way too long (see also my comment on moving the examples to a seperate page)
• What is the use of defining expectation, variance and covariance in this page? It would be better to just link to their pages, without introducing them again.
• My edits on the page before the big update seem to have been lost because of this complete rewrite. As an example, there's no longer a link to Fischer's fundamental theorem of population genetics. Maybe it's just a personal view, but I like edits that are atomic much more than I like monolithic rewrites of pages.

I assume there are different views possible on these comments.

--Anthony Liekens 11:02, 30 Nov 2004 (UTC)

You've just listed a bunch of misgivings I've had myself. I thought well, I'll just do it and see what people think. I would not be offended by any of the rewrites you suggest, and I think I will undertake some of them myself unless you beat me to it. Let's make it a good page. The objections I have to your list are:

• I did try to include everything in the previous page. Fisher's theorem is still there, near the end of the simple Price equation section. Maybe it needs to be put up front as part of an introductory overview.

• I looked at the pages on expected value and covariance and it seemed to me that, for the expected value anyway, there are a number of definitions for discrete, continuous, etc, using a different notation, and there would be a lot of head-scratching unless it was explicitly defined as it is being used in the article.

Another thing I would like to include how kin selection is handled by the Price equation, but I don't feel like I understand it well enough right now to write anything.

Paul Reiser 15:17, 30 Nov 2004 (UTC)

To comment on the old discussion here, it may be useful to define expectation and covariance here because the definitions used here are not the actual definitions of expectation and covariance. The Price equation uses the expectation operator and the covariance function for simplicity; however, the actual definitions of these things are based on estimates from a population. That is, the Price equation really relates ARITHMETIC MEANS from one population to the immediate next population. It says nothing about "expectation" and "covariance." In order to make a statement about expectation and covariance, one would have to introduce probability. However, Price equation has nothing to do with probability. At best, it is a statistical statement.

It would be nice to get rid of ALL references to expectation and covariance and just speak of averages. However, due to rampant misuse over the years, it is expected that expectation and covariance be used with the Price equation. It's unfortunate.

--TedPavlic 17:07, 18 February 2007 (UTC)

[edit] Expectation and Covariance

It makes no sense to me that this article defines expectation and covariance both as means of some property of a finite deterministic population. It seems to me like expectation should simply be mean or average. However, that means that covariance should be replaced with something like mean covariate, where covariate would mean the product of two variates. This actually is similar to the terminology used in ANCOVA.

That being said, it was Price himself who started this whole mess by using these terms. Is it right to reformulate on a Wikipedia page?

I at least think that some extra notes need to be made. Presently using the terms expectation and covariance confuses what the equation actually means. I'm still not sure which terms should be used. Maybe C_xy could be used instead of as a compromise?

--TedPavlic 11:05, 22 February 2007 (UTC)

I think we should stick to the terms used in the literature, whatever they are, and if they are not the most appropriate, we should make a clear note of that in the introduction. I am in favor of people not having to "shift gears" when they go from the Wikipedia article to the literature and back, but they should be very aware of the problem. The Wikipedia article might then serve as a small push in the right direction without staking out non-peer-reviewed territory. PAR 15:57, 22 February 2007 (UTC)