Calculating the Slope of a Line of Best Fit

Points on a scatter graph link different quantities to determine a relationship between them. Sometimes, the points will lack a pattern, indicating no correlation. But when the points do show a correlation, a line of best fit will show the extent of the connection. The sharper the slope of the line through the points, the greater the correlation between the points. The line’s slope equals the difference between points’ y-coordinates divided by the difference between their x-coordinates.

Step 1

Select any two points on the line of best fit. These points may or may not be actual scatter points on the graph.

Step 2

Subtract the first point’s y-coordinate from the second point’s y-coordinate. If, for instance, the two coordinates are (1,4) and (3, 20): 4 – 20 = -16.

Step 3

Subtract the first point’s x-coordinate from the second point’s x-coordinate. Using the same two points as an example: 1 – 3 = -2.

Step 4

Divide the difference in y-coordinates by the difference in x-coordinates: -16 / -2 = 8. The line has a slope of 8.