So you can see that the bottom is the square root of the sum of the squared deviations for x, times the same for y. They will be approximately half positive and half negative, since (usually) about half the values are above the mean and half are below. These Δxi's and Δyi's are called the 'deviations'. Call this ybar.ģ) For every x-value, subtract xbar. Call this xbar.Ģ) Find the mean (average) of all the y-values. If you want to calculate it from data, this is the procedure:ġ) Find the mean (average) of all the x-values. It is always between -1 and 1, with -1 meaning the points are on a perfect straight line with negative slope, and r = 1 meaning the points are on a perfect straight line with positive slope.
