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#1
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Error in formula displayed for linear and 2nd order curve fits inExcel 2003
I have created trendlines for some pretty simple data using both 2nd
order polynomial and linear fits. In both cases, the displayed formulas have their 1st and 2nd order coefficients wrong by a factor of 10!! (I have read lots of posts about increasing precision but this is not what I am up against). Has anyone seen this? |
#2
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Error in formula displayed for linear and 2nd order curve fits in Excel 2003
What version of Excel? Could you include the data in a follow up post (not
as an attachment), along with the coefficients you've computed? - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ wrote in message ... I have created trendlines for some pretty simple data using both 2nd order polynomial and linear fits. In both cases, the displayed formulas have their 1st and 2nd order coefficients wrong by a factor of 10!! (I have read lots of posts about increasing precision but this is not what I am up against). Has anyone seen this? |
#3
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Error in formula displayed for linear and 2nd order curve fits inExcel 2003
I am using Office 2003 Standard, SP3
Here is the data for the linear trend: Density 0.1 0.2 0.3 0.4 0.5 0.6 Throughput 3.125 2.726 2.378 2.061 1.742 1.452 The trendline formula displayed is y=-.3324x+3.4107 If use either SLOPE or just do a simple manual (delta y/delta x) slope calcualtion, you get -3.324 For the 2nd order trend here is the data: Density 0.1 0.2 0.3 0.4 Throughput 6.27 4.9 3.75 2.87 The formula displayed is y = 0.1225x^2 - 1.7475x + 7.8975. Using another stats package I did a curve fit and got y=12.225x^2 - 17.475x + 7.8975, which yeilds correct ys for the given xs. Interestingly, the 2nd order coefficient seems to be out by a factor of 100 (10^2), while 1st order seems to be off by a factor of 10 (10^1). Richard On Jun 19, 11:54*am, "Jon Peltier" wrote: What version of Excel? Could you include the data in a follow up post (not as an attachment), along with the coefficients you've computed? - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. -http://PeltierTech.com _______ wrote in message ... I have created trendlines for some pretty simple data using both 2nd order polynomial and linear fits. *In both cases, the displayed formulas have their 1st and 2nd order coefficients wrong by a factor of 10!! (I have read lots of posts about increasing precision but this is not what I am up against). *Has anyone seen this?- Hide quoted text - - Show quoted text - |
#4
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Error in formula displayed for linear and 2nd order curve fits in Excel 2003
Make an XY chart, not a line chart. A line chart counts categories as 1, 2,
3, etc., regardless of the numeric values in the cells. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. - http://PeltierTech.com _______ wrote in message ... I am using Office 2003 Standard, SP3 Here is the data for the linear trend: Density 0.1 0.2 0.3 0.4 0.5 0.6 Throughput 3.125 2.726 2.378 2.061 1.742 1.452 The trendline formula displayed is y=-.3324x+3.4107 If use either SLOPE or just do a simple manual (delta y/delta x) slope calcualtion, you get -3.324 For the 2nd order trend here is the data: Density 0.1 0.2 0.3 0.4 Throughput 6.27 4.9 3.75 2.87 The formula displayed is y = 0.1225x^2 - 1.7475x + 7.8975. Using another stats package I did a curve fit and got y=12.225x^2 - 17.475x + 7.8975, which yeilds correct ys for the given xs. Interestingly, the 2nd order coefficient seems to be out by a factor of 100 (10^2), while 1st order seems to be off by a factor of 10 (10^1). Richard On Jun 19, 11:54 am, "Jon Peltier" wrote: What version of Excel? Could you include the data in a follow up post (not as an attachment), along with the coefficients you've computed? - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. -http://PeltierTech.com _______ wrote in message ... I have created trendlines for some pretty simple data using both 2nd order polynomial and linear fits. In both cases, the displayed formulas have their 1st and 2nd order coefficients wrong by a factor of 10!! (I have read lots of posts about increasing precision but this is not what I am up against). Has anyone seen this?- Hide quoted text - - Show quoted text - |
#5
Posted to microsoft.public.excel.charting
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Error in formula displayed for linear and 2nd order curve fits inExcel 2003
On Jun 19, 12:46*pm, "Jon Peltier"
wrote: Make an XY chart, not a line chart. A line chart counts categories as 1, 2, 3, etc., regardless of the numeric values in the cells. - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. -http://PeltierTech.com _______ wrote in message ... I am using Office 2003 Standard, SP3 Here is the data for the linear trend: Density * * * * * 0.1 * * * * * 0.2 * * * * 0..3 0.4 * * * * * * 0.5 * * * * * 0.6 Throughput * * 3.125 * * 2.726 2.378 2.061 1.742 1.452 The trendline formula displayed is y=-.3324x+3.4107 If use either SLOPE or just do a simple manual (delta y/delta x) slope calcualtion, you get -3.324 For the 2nd order trend here is the data: Density * * * * * 0.1 * * * * * 0.2 * * * * 0..3 * * * *0.4 Throughput * * *6.27 * * *4.9 * *3.75 2.87 The formula displayed is y = 0.1225x^2 - 1.7475x + 7.8975. *Using another stats package I did a curve fit and got y=12.225x^2 - 17.475x + 7.8975, which yeilds correct ys for the given xs. *Interestingly, the 2nd order coefficient seems to be out by a factor of 100 (10^2), while 1st order seems to be off by a factor of 10 (10^1). Richard On Jun 19, 11:54 am, "Jon Peltier" wrote: What version of Excel? Could you include the data in a follow up post (not as an attachment), along with the coefficients you've computed? - Jon ------- Jon Peltier, Microsoft Excel MVP Tutorials and Custom Solutions Peltier Technical Services, Inc. -http://PeltierTech.com _______ Well that explains it perfectly (including my observation about the coefficients)! Doesn't seem intuitive to me that a line chart would do that but at least now I know. Thanks. Richard wrote in message .... I have created trendlines for some pretty simple data using both 2nd order polynomial and linear fits. In both cases, the displayed formulas have their 1st and 2nd order coefficients wrong by a factor of 10!! (I have read lots of posts about increasing precision but this is not what I am up against). Has anyone seen this?- Hide quoted text - - Show quoted text -- Hide quoted text - - Show quoted text - |
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