Trend lines in charts under Excel

[cloclo]

Something I have discovered for long but which continues with Excel
2007 (under XP): when you draw a trend line in a scatter or line chart
I generally get either not the best fit (or equation) and/or almost
sytematically the wrong equation associated to this trend line.

Has anybody seen that already and moreover knows why it is like that?
Surprising from a company like Micosoft.

 

[Mike Middleton]

cloclo -

Please provide an example.

In my experience, Excel trend line provides best fit for a linear function
in an XY (Scatter) chart type.

For non-linear functions, the trend line is based on transforms of the
original data, and often you could obtain a better fit using Solver to
search for function parameter values.

For a Line chart type, the trend line uses 1,2,3,... for the X values of the
fitted equation, ignoring any numerical values you may be using as labels
for the horizontal axis.

- Mike
http://www.MikeMiddleton.com