I made a scatter chart of some data in Excel 2007 and placed a power fit
trendline that resulted in the equation y=0.075x^-0.06 with a R^2 of 0.983.
If I try to back calculate data points based on this model I get values that
differ from the input data. I took the exact same data in Excel 2003 and I
get a different equation (y=0.1001x^-0.0572) and R^2 (0.9931). I used this
equation to back calculate some input values and it worked perfect. Is there
an error with the equation reporting routine in Excel 2007? My OS is XP HOME
SPII



----------------
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Make sure in both cases you use an XY chart, not a line chart. Also, expand
the number format of the regression formula to display as many digits as
possible, using a scientific format with lots of decimal places,

- Jon
-------
Jon Peltier, Microsoft Excel MVP
Tutorials and Custom Solutions
http://PeltierTech.com
_______


"SPWelch" wrote in message
...
I made a scatter chart of some data in Excel 2007 and placed a power fit
trendline that resulted in the equation y=0.075x^-0.06 with a R^2 of
0.983.
If I try to back calculate data points based on this model I get values
that
differ from the input data. I took the exact same data in Excel 2003 and I
get a different equation (y=0.1001x^-0.0572) and R^2 (0.9931). I used this
equation to back calculate some input values and it worked perfect. Is
there
an error with the equation reporting routine in Excel 2007? My OS is XP
HOME
SPII



----------------
This post is a suggestion for Microsoft, and Microsoft responds to the
suggestions with the most votes. To vote for this suggestion, click the "I
Agree" button in the message pane. If you do not see the button, follow
this
link to open the suggestion in the Microsoft Web-based Newsreader and then
click "I Agree" in the message pane.

http://www.microsoft.com/office/comm...excel.charting

If you still have problems, send me the file (not to newsgroup but to
private email)
I would like to check this out.
--
Bernard V Liengme
www.stfx.ca/people/bliengme
remove caps from email

"SPWelch" wrote in message
...
I made a scatter chart of some data in Excel 2007 and placed a power fit
trendline that resulted in the equation y=0.075x^-0.06 with a R^2 of
0.983.
If I try to back calculate data points based on this model I get values
that
differ from the input data. I took the exact same data in Excel 2003 and I
get a different equation (y=0.1001x^-0.0572) and R^2 (0.9931). I used this
equation to back calculate some input values and it worked perfect. Is
there
an error with the equation reporting routine in Excel 2007? My OS is XP
HOME
SPII



----------------
This post is a suggestion for Microsoft, and Microsoft responds to the
suggestions with the most votes. To vote for this suggestion, click the "I
Agree" button in the message pane. If you do not see the button, follow
this
link to open the suggestion in the Microsoft Web-based Newsreader and then
click "I Agree" in the message pane.

http://www.microsoft.com/office/comm...excel.charting

Did anyone find out anything about this problem with Excel 2007?

I did a similar power trend line and got the formula y = 14371x^-.025 with
R^2=0.978. The results from that formula plotted on the graph were no where
near the trend line drawn on the graph.

I modified the formula to y = 13200x^-0.25 and the plotted graph is now
superimposed on the trend line.

Thanks,

John

"Bernard Liengme" wrote in message
...
If you still have problems, send me the file (not to newsgroup but to
private email)
I would like to check this out.
--
Bernard V Liengme
www.stfx.ca/people/bliengme
remove caps from email

"SPWelch" wrote in message
...
I made a scatter chart of some data in Excel 2007 and placed a power fit
trendline that resulted in the equation y=0.075x^-0.06 with a R^2 of
0.983.
If I try to back calculate data points based on this model I get values
that
differ from the input data. I took the exact same data in Excel 2003 and
I
get a different equation (y=0.1001x^-0.0572) and R^2 (0.9931). I used
this
equation to back calculate some input values and it worked perfect. Is
there
an error with the equation reporting routine in Excel 2007? My OS is XP
HOME
SPII



----------------
This post is a suggestion for Microsoft, and Microsoft responds to the
suggestions with the most votes. To vote for this suggestion, click the
"I
Agree" button in the message pane. If you do not see the button, follow
this
link to open the suggestion in the Microsoft Web-based Newsreader and
then
click "I Agree" in the message pane.

http://www.microsoft.com/office/comm...excel.charting