Idential trend line equations show different trends

[Wired PSF]

Hi

I have plotted a trend line based on some actual known data. I hav
then manually calculated the y figure by plugging in the trend lin
formula.

y = 5E-05x4 - 0.0283x3 + 5.4408x2 - 521.05x + 29719

On that attachment you can see a difference in results even though it
the same trend line.

Any ideas?

Thanks

Wire

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[Mike Middleton]

Wired PSF -

(1) Use considerably more significant digits (up to 15) in your
calculations. The first term, 0.00005*x^4, lacks precision.

(2) Avoid overfitting your data. A polynomial of order 4 is seldom
appropriate.

- Mike
http://www.mikemiddleton.com

 

[Lamb Chop]

Also try to check the t-values of each coefficients.

Try to use LINEST function.

Note: LINEST is a matrix function. You need to enter the formula by
ctrl-shift-enter rather than just enter. See the help function from
LINEST. It will tell you more about multivariable regressions.

Also note that office2k and office may give slightly different results if
your variables are inter-related.

Man