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timothyfoley_NENSP@yahoo.
science forum beginner

Joined: 23 Apr 2006
Posts: 2

Posted: Sun Apr 23, 2006 10:09 pm    Post subject: Algebraic computation of the Hat diagonal

I would like to compute studentized residuals for predicted
concentrations in assays that use first order and second order
polynomial regression, as well as non-linear 4-parameter logistic
models.

Does anyone have an algebraic solution that can be used in Excel to
compute hii in these applications. I would like to use studentized
residuals to assess the prediction quality of calibration models used
in biomedical assays.

Basically, I would like to compute the following:

t = Cal (actual) - Cal (estimated)/RMSE * SQRT (1- hii).

RMSE is computed as SQRT [Sum (cal actual - cal estimated)^2/n-p]

The Hii statistic would adjust the ratio in the preceding equation for

leverage. Calibration points with t values that are greater than 2.5 or

3 would be candidates for elimination from the the current calibration.

I was initially going to ignore leverage issues, but since many of the
calibrations I deal with have a wide dynamic range, I thought I would
include hii in the estimate of t.

The main issue is that I need to find an algebraic approximation for
the matrix operations for ease of use. Can anyone supply formulas or
better yet a macro? Advice from the chemometrically inclined would be
most welcome.

Thanks,
Tim

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