```Date: Nov 27, 2012 3:22 PM
Author: Ray Koopman
Subject: Re: OK – I think I’m set, at least till we get t<br>	o c on (e, u, u*e).

On Nov 27, 6:19 am, djh <halitsk...@att.net> wrote:> 1.>> You wrote:>> ?slope = dy/dx = a1 + 2*a2*x?>> Oh! That slope! (Of the tangent to the quadratic at x = 0.) Duh!>> I was construing ?slope? as just a alternative term for ?coefficient?> ? don?t know why. Someday I?ll learn if that if I can?t make sense> of something you?ve written, then I?ve construed something wrongly.>> 2.>> When I re-run the analysis, I will use (u/1+u) instead of u. So I> assume I would use ln(u/(1+u)), and (ln(u+(1/u)))^2, parallel to> ln(u) and (ln(u))^2? (Unless you don?t want me to take logs ? please> clarify here.)I intended no logs. Also, I worry when I see u/1+u and u+(1/u),neither of which equals u/(1+u).>> 3.  You wrote:>> ?For instance, you might get the slope at each data point and then> use their literal average, a1 + 2*a2*mean_x. But what if cells with> different x-means give the same a1 and a2? Should their "average> slope" measures be the same or different? That's the kind of question> you have to ask yourself.?>> Since I can?t think that far ahead in the abstract (as you can), I> will use ?a1 + 2*a2*mean_x? initially, and see if any peculiarities> arise of the sort you mention (or others.)Here's a f'rinstance. First, remember that a quadratic can always bewritten as A + B*(x - C)^2. Next, suppose that two cells have thesame A,B,C, but mean_x is < C in one cell and > C in the other, sothat their average slopes differ. Then, if the difference in mean_xis an intrinsic property of the cells then the average slope isappropriate, but if the difference in mean_x is arbitrary, a resultof experimenter whim, then the average slope is not appropriate.>> 4.>> [...]I'll respond to 4 later.
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