Statistical Significance

I would venture to suggest that you have the beginnings of the thought noted, and would guess that what you are really after is a solid statistical test for significance that you can apply to the data. I am not enough of a statistician to state what test you should use, nor am I familiar enough with those tests to instruct you. I will recommend this tutorial as a starting place for researching these statistical tests and how to perform them: http://stattrek.com/regression/slope...?Tutorial=Stat

I don't know if there is much difference to using the CORREL() function or not. I believe there are statistical tests designed around the Pearson correlation coefficient that are roughly equivalent to the test designed around the regression slope. I think it all eventually comes down to the statistical question of exactly what statistical test you decide is most appropriate for the determination you want to make. Once you decide which test to perform, then you can research the test statistic and other elements of the test, then determine how those quantities are calculated using Excel's functions.

CORREL (or PEARSON, same, same) returns the correlation coefficient R, and the chart shows R^2 -- so all the same measure.