EXCEL polynomial trendlines

  • Thread starter Thread starter Fraser Johnson
  • Start date Start date
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Fraser Johnson

I have been generating trendlines to a number of data set's using a
polynomial fit. If I do not set the intercept to zero the equation indicated
on the graph is correct when I re-generate the trendline curve using second
data set inputing x to obtain y.

However, if I set the intercept to pass through zero the equation given does
not give the correct trendline when I regenerate the curve using a new input
data set for x to obtain y.

Doe anyone have any suggestions of comments as to why this is happening and
what can do to stop it?
 
I am sure your post makes sense to you but it leaves at least me quite
confused.

You are getting the correct trendline with a non-zero intercept and an
incorrect one with the intercept set to zero.

I am not sure what exactly you expect the answer to be to "...why is
it happening?" I guess because one is correct and the other is not?

And, what is it that you want to stop?

On Thu, 20 Aug 2009 03:49:02 -0700, Fraser Johnson <Fraser
I have been generating trendlines to a number of data set's using a
polynomial fit. If I do not set the intercept to zero the equation indicated
on the graph is correct when I re-generate the trendline curve using second
data set inputing x to obtain y.

However, if I set the intercept to pass through zero the equation given does
not give the correct trendline when I regenerate the curve using a new input
data set for x to obtain y.

Doe anyone have any suggestions of comments as to why this is happening and
what can do to stop it?
Click to expand...
Regards,

Tushar Mehta
Microsoft MVP Excel 2000-present
www.tushar-mehta.com
Excel and PowerPoint tutorials and add-ins
 
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