Correlation Coefficients for 2nd & 3rd Order Curves

[Guest]

I am doing a comparison of COD results in mg/L vs. Absorbance readings. I have plotted the values for a linear curve and 2nd and 3rd order curves. I have been able to produce the polynomial equations associated with each, but here is my problem...

I am having difficulty producing the correlation coefficients for the 2nd & 3rd order curves. I have plotted the points and added the corresponding trendlines, however when I have the equation for the trendline added to the graph, it does not match up to the one I calculated using the LINEST array function. (I have back-calculated using the x values and know that the LINEST equations are correct.) Why is the equation coming up wrong on the graph?

Also, Mr. Bernard Liengme, if you are reading this question...

I have been able to duplicate the example on your website and found that the graphs and equations all match up with your example. Which is why I am now doubly confused as to why I am having problems.

Any advice would be greatly appreciated! I am sure that I have left out one minute detail somewhere that is causing this hick-up, but I can't seem to find it!

Thanks!
Cindy Covey

 

[Mike Middleton]

Cindy Covey -

Why is the equation coming up wrong on the graph? <

If you're using a Line chart type, the trendline uses 1,2,3,... for x values
(ignoring the x axis labels).

If you're using an XY (Scatter) chart type, the trendline uses 1,2,3,... for
x values if any of the chart's data values in worksheet cells are
non-numeric.

- Mike Middleton, www.usfca.edu/~middleton