## The Correlation Coefficient:

In the first part of this tutorial, we saw how to use the trendline feature in
Excel to fit a straight line through calibration data and obtain both
the equation of the best-fit straight line and the correlation
coefficient, *R* (often reported as *R*^{2}).
There are in fact various correlation coefficients, but the one we are
interested in here is the Pearson or product-moment correlation
coefficient. The Pearson *R* value provides a measure of the degree to
which the values of *x* and *y* are linearly correlated. We can
assess this visually using a scatter plot (Figure 1), in which we also mark the
centroid of the data, .

Figure 1 - XY scatter plot showing the centroid of the data