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#1
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using polynomial trendline equations
I am using trendline feature in charting to develop a third order polynomial
equation. The fit is good and I want to use the displayed equation to calculate nondata point values. I cannot get the equation to generate points within the original data set. Is there a conversion factor I need to use or is there a way to output the trendline equation differently? The trendline coefficients don't seem to correspond to the data set even though the graph and r-value look good. |
#2
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using polynomial trendline equations
1. Use an XY chart, not a line chart.
2. Use as many digits as Excel will provide. Right-click the formula, choose Format, and on the Number tab, choose a Scientific format with 15 digits after the decimal. 3. Don't use it for extrapolating. Poly fits go haywire rapidly outside of the range they were computed over. Even better than manually copying the trendline formula and parsing out the coefficients, at least in Excel 2003) is to calculate the coefficients in the worksheet using LINEST. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ "john s" wrote in message ... I am using trendline feature in charting to develop a third order polynomial equation. The fit is good and I want to use the displayed equation to calculate nondata point values. I cannot get the equation to generate points within the original data set. Is there a conversion factor I need to use or is there a way to output the trendline equation differently? The trendline coefficients don't seem to correspond to the data set even though the graph and r-value look good. |
#3
Posted to microsoft.public.excel.charting
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using polynomial trendline equations
You may want to check
Trendline Coefficients and Regression Analysis http://www.tushar-mehta.com/publish_...nalysis/16.htm On Fri, 25 Jul 2008 11:49:32 -0700, john s wrote: I am using trendline feature in charting to develop a third order polynomial equation. The fit is good and I want to use the displayed equation to calculate nondata point values. I cannot get the equation to generate points within the original data set. Is there a conversion factor I need to use or is there a way to output the trendline equation differently? The trendline coefficients don't seem to correspond to the data set even though the graph and r-value look good. Regards, Tushar Mehta Microsoft MVP Excel 2000-2008 www.tushar-mehta.com Tutorials and add-ins for Excel, PowerPoint, and other products |
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