[Ifeffit] LCF analysis

Wayne W Lukens Jr wwlukens at lbl.gov
Mon Oct 25 11:24:53 CDT 2010


Hi Scott,

You are correct. That is a much better way to explain it.

Sincerely,

Wayne

On Mon, Oct 25, 2010 at 9:07 AM, Scott Calvin <dr.scott.calvin at gmail.com>wrote:

> On Oct 25, 2010, at 8:25 AM, Wayne W Lukens Jr wrote:
>
> A more useful way to look at this is that the probabilities that A, B and C
> are present are 99.99999999%, 93%, and 77%, respectively.
>
>
> An excellent post, Wayne, but I don't think that last statement is quite
> right. If the F-test gives a probability of 0.23 for material C, I believe
> it's saying that there is a 23% that, given the noise level in the data, the
> fit would indicate that C was present when it was not. That is *not* the
> same thing as saying there is a 77% chance of C being present.
>
> To see this, imagine very, very noisy data. Including C in the fit might
> very well improve the fit in the sense of an R-factor--maybe, in fact,
> there's a 45% chance of a modest improvement with a given set of very noisy
> data, even if there's no C present. That does not mean that a result like
> that should lead to the conclusion that C is more likely than not present
> (55%).
>
> --Scott Calvin
> Sarah Lawrence College
>
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