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Started By
Message
Excel help
Posted on 9/15/15 at 9:07 am
Posted on 9/15/15 at 9:07 am
I have two columns of data to be plotted in simple Y vs X fashion:
X
8.105
7.620
7.186
6.688
6.339
5.772
Y
1260
3790
10050
30300
60450
189300
I then need to fit the data to an appropriate regression, and I need that equation.
Using that equation, I would like to use an X value of 6.270 to calculate the corresponding Y value.
When I use a 4th order polynomial (R=0.9999) I get a Y value of -3x10^6, which cannot be correct. However when I use a power fit, I get the reasonable value of 6.58x10^4. Why is the calculation using the polynomial fit so off? I've done the calculation in both Excel and by hand using a calculator.
I'm sure I'm missing something very basic, so apologies in advance.
X
8.105
7.620
7.186
6.688
6.339
5.772
Y
1260
3790
10050
30300
60450
189300
I then need to fit the data to an appropriate regression, and I need that equation.
Using that equation, I would like to use an X value of 6.270 to calculate the corresponding Y value.
When I use a 4th order polynomial (R=0.9999) I get a Y value of -3x10^6, which cannot be correct. However when I use a power fit, I get the reasonable value of 6.58x10^4. Why is the calculation using the polynomial fit so off? I've done the calculation in both Excel and by hand using a calculator.
I'm sure I'm missing something very basic, so apologies in advance.
8
Posted on 9/15/15 at 9:08 am to Sigma
Turn it off then turn it on again.
Posted on 9/15/15 at 9:09 am to Sigma
The answer is 288 (or 2, depending on whether you multiply or divide first)
Posted on 9/15/15 at 9:09 am to Sigma
Help Board
Posted on 9/15/15 at 9:24 am to Sigma
quote:
Turn it off then turn it on again.
Posted on 9/15/15 at 9:26 am to Sigma
X=about tree fiddy
Posted on 9/15/15 at 9:31 am to Sigma
=5*10^12*EXP(-2.878*X)
This post was edited on 9/15/15 at 9:34 am
Posted on 9/15/15 at 9:31 am to Sigma
quote:First of all just because you got an R = 0.999 doesn't mean your line is a good fit. People who throw data into Excel and quote this number don't know jack.
When I use a 4th order polynomial (R=0.9999) I get a Y value of -3x10^6, which cannot be correct. However when I use a power fit, I get the reasonable value of 6.58x10^4. Why is the calculation using the polynomial fit so off? I've done the calculation in both Excel and by hand using a calculator.
I'm sure I'm missing something very basic, so apologies in advance.
The reason power function is a better fit is rooted in the nature of your data. Generally biological data that shows growth is best fitted using a power function.
Posted on 9/15/15 at 11:16 am to Sigma
I get 68,167 using an exponential function. Just using the "Add trend line" in XLS. The equation is 5E+10e^-2.154x
R Sq = 0.9991
R Sq = 0.9991
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