EXCEL polynomial trendlines

[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?

 

[Tushar Mehta]

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?

Regards,

Tushar Mehta
Microsoft MVP Excel 2000-present
www.tushar-mehta.com
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