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#1
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Idential trend line equations show different trends
Hi I have plotted a trend line based on some actual known data. I have then manually calculated the y figure by plugging in the trend line formula. y = 5E-05x4 - 0.0283x3 + 5.4408x2 - 521.05x + 29719 On that attachment you can see a difference in results even though its the same trend line. Any ideas? Thanks Wired +-------------------------------------------------------------------+ |Filename: dummy data.gif | |Download: http://www.excelforum.com/attachment.php?postid=5103 | +-------------------------------------------------------------------+ -- Wired PSF ------------------------------------------------------------------------ Wired PSF's Profile: http://www.excelforum.com/member.php...o&userid=36795 View this thread: http://www.excelforum.com/showthread...hreadid=565052 |
#2
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Idential trend line equations show different trends
Wired PSF -
(1) Use considerably more significant digits (up to 15) in your calculations. The first term, 0.00005*x^4, lacks precision. (2) Avoid overfitting your data. A polynomial of order 4 is seldom appropriate. - Mike http://www.mikemiddleton.com "Wired PSF" wrote in message ... Hi I have plotted a trend line based on some actual known data. I have then manually calculated the y figure by plugging in the trend line formula. y = 5E-05x4 - 0.0283x3 + 5.4408x2 - 521.05x + 29719 On that attachment you can see a difference in results even though its the same trend line. Any ideas? Thanks Wired +-------------------------------------------------------------------+ |Filename: dummy data.gif | |Download: http://www.excelforum.com/attachment.php?postid=5103 | +-------------------------------------------------------------------+ -- Wired PSF ------------------------------------------------------------------------ Wired PSF's Profile: http://www.excelforum.com/member.php...o&userid=36795 View this thread: http://www.excelforum.com/showthread...hreadid=565052 |
#3
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Idential trend line equations show different trends
Also try to check the t-values of each coefficients.
Try to use LINEST function. Note: LINEST is a matrix function. You need to enter the formula by ctrl-shift-enter rather than just enter. See the help function from LINEST. It will tell you more about multivariable regressions. Also note that office2k and office may give slightly different results if your variables are inter-related. Man "Mike Middleton" wrote in message ... Wired PSF - (1) Use considerably more significant digits (up to 15) in your calculations. The first term, 0.00005*x^4, lacks precision. (2) Avoid overfitting your data. A polynomial of order 4 is seldom appropriate. - Mike http://www.mikemiddleton.com "Wired PSF" wrote in message ... Hi I have plotted a trend line based on some actual known data. I have then manually calculated the y figure by plugging in the trend line formula. y = 5E-05x4 - 0.0283x3 + 5.4408x2 - 521.05x + 29719 On that attachment you can see a difference in results even though its the same trend line. Any ideas? Thanks Wired +-------------------------------------------------------------------+ |Filename: dummy data.gif | |Download: http://www.excelforum.com/attachment.php?postid=5103 | +-------------------------------------------------------------------+ -- Wired PSF ------------------------------------------------------------------------ Wired PSF's Profile: http://www.excelforum.com/member.php...o&userid=36795 View this thread: http://www.excelforum.com/showthread...hreadid=565052 |
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