Results of trend line in Excel
 

I fitted some data using the trend line tool. The fit purportedly was a 3-rd
order polynmial. When I create a column of values using the coefficients
that Excel found (Display equation), I find the data does not overlay the
trend line. I created data in the range of the fit so there is no error due
to extrapolation and the fit R value was 0.9999. Is there an error in the
routine that reports the coefficients for polynomial fits? If so, is the re
a patch or work around?

Thanks

Results of trend line in Excel
 

The most likely cause is that you are working with two few digits. If you
format the trendline equation to display more digits I am sure you will find
all is well,
Of course, this problem of copying values from the equation is fraught with
problems - typos resulting from arthritic fingers or from poor reading
glasses being some of them
Best to use LINEST to get the coefficients into cells; see
http://www.stfx.ca/people/bliengme/E...Polynomial.htm

best wishes
--
Bernard V Liengme
www.stfx.ca/people/bliengme
remove caps from email

"E0sysengiineer" wrote in message
...
I fitted some data using the trend line tool. The fit purportedly was a
3-rd
order polynmial. When I create a column of values using the coefficients
that Excel found (Display equation), I find the data does not overlay the
trend line. I created data in the range of the fit so there is no error
due
to extrapolation and the fit R value was 0.9999. Is there an error in the
routine that reports the coefficients for polynomial fits? If so, is the
re
a patch or work around?

Thanks