Fri, 4 Jan 2008 08:31:04 -0800 from Donal P
:
I'm using Excel 2003 under XP Professional to examine the relationship, if
any, between two sets of data - let's call them 'audit score' and 'profit'.
I have 74 data points for each set. When I graph the data points in an XY
scatterplot and then add a trendline to the data series, I get a slope for
the line of .033. However, when I use the correlation function in data
analysis, I get a .0185.

I thought these two numbers should be the same.

Their sign are the same, but not their values.

Overview: the correlation is how closely the points lie to a line,
and the slope is the steepness of that line.

Details:

The correlation coefficient is always between -1 and +1 inclusive.
It measures how close the points lie to the best fitting line. r = -1
means the points line up precisely on a line sloping down to the
right; r = +1 means they align precisely on a line sloping up to the
right. r = .9 means they lie in a good up-to-the-right relationship,
but not perfectly linear; r = .8 means less perfectly linear, and so
on down to r = 0, which is no linear relationship at all. Then with r
= -.1, -.2, and so on, the relationship gets closer and closer to a
straight line, but pointing down toward the right.

--
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http://OakRoadSystems.com/
"If there's one thing I know, it's men. I ought to: it's
been my life work." -- Marie Dressler, in /Dinner at Eight/