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#1
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trendline equations are incorrect
I charted a set of coordinates. The polynomial equation
fit extremely well (r square = 0.99) Unless I'm doing something wrong, (and I don't think I am; I had someone else look at it as well) the equation is incorrect. Is this a bug in excel 2002? |
#2
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trendline equations are incorrect
On Tue, 16 Sep 2003 16:04:21 -0700, "Fred" wrote:
I charted a set of coordinates. The polynomial equation fit extremely well (r square = 0.99) Unless I'm doing something wrong, (and I don't think I am; I had someone else look at it as well) the equation is incorrect. Is this a bug in excel 2002? It depends. Is the formula you are writing about the one displayed on the chart? If so, it is unlikely to be incorrect. What is more likely is that you have not formatted the formula to show enough decimal places to be accurate. Double click on the box that contains the equation. A Format Data Label dialog box will open and should have a number option. (If it does not, then you selected the contents of the label, rather than the label). Format the number to 10 or 15 decimal places and use the resultant formula. --ron |
#3
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trendline equations are incorrect
A safer approach is to use scientific notation with with 14 deciam
places. Without scientific notation, there is no guarantee that the coefficients are scaled such that any fixed number of decimal places will be enough. Jerry Ron Rosenfeld wrote: On Tue, 16 Sep 2003 16:04:21 -0700, "Fred" wrote: I charted a set of coordinates. The polynomial equation fit extremely well (r square = 0.99) Unless I'm doing something wrong, (and I don't think I am; I had someone else look at it as well) the equation is incorrect. Is this a bug in excel 2002? It depends. Is the formula you are writing about the one displayed on the chart? If so, it is unlikely to be incorrect. What is more likely is that you have not formatted the formula to show enough decimal places to be accurate. Double click on the box that contains the equation. A Format Data Label dialog box will open and should have a number option. (If it does not, then you selected the contents of the label, rather than the label). Format the number to 10 or 15 decimal places and use the resultant formula. --ron |
#4
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trendline equations are incorrect
Fred -
I charted a set of coordinates. The polynomial equation fit extremely well (r square = 0.99) Unless I'm doing something wrong, (and I don't think I am; I had someone else look at it as well) the equation is incorrect. Is this a bug in excel 2002? In addition to being sure to display enough significant digits for the coefficients, be sure to use an XY (Scatter) chart type. Do not use a Line chart type (in which case the trendline fit uses 1,2,3,... for the X values). - Mike Middleton, www.usfca.edu/~middleton |
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