I am not clear about your example; what model did you fit to this data, what
results did you get, and why did you think that LINEST gave you more accurate
results than the chart trendline?

When I fit this data with a polynomial of degree 3 or less in Excel 2003,
LINEST and the chart trendline agree sufficiently that it did not seem worth
determining which was more accurate. In your earlier note, you mentioned a
6th degree polynomial, which I would hesitate to fit to this data since it
has such a narrow range of x -values. Ignoring those misgivings, I found
that for a 6th degree polynomial LINEST gave 0 correct figures for every
coefficient, while the chart trendline gave approximately 10 correct figures
for each of the 7 coefficients.

Jerry

"BOS" wrote:

Try this dataset:
X Y
0.76 173
0.77 214
0.78 255
0.79 275.5
0.8 296
0.81 306
0.82 316
0.83 326.5
0.84 337
0.85 345
0.86 353
0.87 361
0.88 369
0.89 374.5
0.9 380
0.91 382.5
0.92 385
0.93 387.5
0.94 390
0.95 392.5
0.96 395
0.97 397
0.98 399
0.99 399
1 399



"Jerry W. Lewis" wrote:

Please give an example where the trendline in 2003 gives worse results than
LINEST. Prior to 2007, the chart polynomial trendline algorithm was
excelent, and such claims usually involved user error such as using a Line
chart instead of a Scatter chart, or failure to display enough figures for
the chart trendline coefficients.

Jerry

"BOS" wrote:

It looks like there is a problem when the trendline calculates the
coefficient for datasets that are way off from the origin. I found the same
problem. The fitted curve looks great but the coefficients are way off. The
regression algorithm does much better. If the dataset is translated around
the means; i.e., use (x-xaverage) and y-yaverage), the trendline predicted
values also comes out pretty good. The regression algorithm will presumably
differences and perform the regression on the differences, just like the
regression add-in. the fact that the trendline curve is usually pretty good
especially if you go to the sixth order polynomial, means that the regression
is ok, but the reporting of the coefficients when it translates back to the
original dataset is in error. The same results are obtained whether in XP,
2003 or 2007. Microsoft should pay attention!

"John1791" wrote:

I am trying to work with trendlines, and I can match my data with a
polynominal trendline. The plotted trendline matches the data points very
closely, but when I apply the formula generated to actual data, my projected
values are way off. I believe the problem is that the displayed formula is
rounding constants off and not displaying to the number of significant
figures required to generate a workable formula.

Are there any ways to change any settings to allow Excel to display more
figures in the diplayed trendline formulas?

Thank you in advance.