# [Ifeffit] How to calculate F-value for XANES PCA results

Andrew acampo2 at tigers.lsu.edu
Sun Jan 10 14:12:18 CST 2010

```Hi everyone,

I was looking through the literature on how to handle PC analysis data and
saw that there are several different methods you can use for determining how
many components there are in the series of scans. Included in SixPack are
the indicator function, scree test, and the ability to quickly do the
reduced eigenvalue ratios. I've been digging through the literature as to
how to calculate the F-values. The closest to an answer that I got was:

"The above-mentioned reduction of the body of experimental data, that is,
the decision of what components correspond to the noise and what are the
principal components, is now made on the basis of an F test of the variance
associated with eigenvalue k and the summed variance associated with noise
eigenvalues (k+1, ..., c). The null hypothesis is that a given factor k is a
member of the pool of noise factors. The probability that an F value would
be higher than the current value is given by %SL (percentage of significance
level). Thus, the kth factor is accepted as a principal component if %SL is
lower than some test level." (Garcia 1995).

We ran the PCA on the reduction of iron while scanning at increased
temperatures. I checked the foil standard but did not see any shift in the
max at 7112, we scanned at 0.5 eV intervals (2 eV resolution at the beam). I
thought I understood what that statement was saying but I'm almost certain
I'm doing something wrong. I have attached the .xlsx file that I was working
on and hope someone can point me to the right direction. The file includes
the components of the PCA and some of the variances that I was calculating.
If there is a paper that someone shows an actual calculation of this in the
supplemental materials that would have been exactly what I was looking for!

Thanks for the help!

Andrew Campos

Fernandez-Garcia, M., C. Marquez Alvarez, and G.L. Haller, The Journal of
Physical Chemistry, 1995, 99(33), 12565-12569.

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