I'd like to use these data to derive an equation using Excel.
300 13
310 12.6
320 12.2
330 11.8
340 11.4
350 11
360 10.8
370 10.6
380 10.4
As x goes up, y goes down. Seems straightforward. But when I do a polynomial regression on these data, even though the trendline matches the data pretty well, the equation it generates doesn't work. The equation is When I plug in x values to that equation, the numbers go up! So something is pretty wrong here.
My steps:
place both number series in excel
select the second set (13, 12.6 ...)
plot a line graph
set the first set as the x axis labels
select Series1 and add a polynomial (2) trendline, display equation, display R-squared
That produces the equation above, with an R^2 value of .9955. But when I use that equation, it doesn't produce those outputs for those inputs.
Clearly I'm doing something wrong.