• The formulas used are:

b = (n Σxy − Σx Σy) ÷ (n Σx² − (Σx)²)

a = ȳ − b x̄

1. where x̄ = Σx ÷ n is the mean of the x-values
2. and ȳ = Σy ÷ n is the mean of the y-values.

1. Find n, Σx, Σy, Σxy and Σx².
2. Calculate the slope b using the formula above.
3. Calculate x̄ and ȳ, then calculate the intercept a.
4. Write the equation ŷ = a + bx. As a check, the line always passes through the point (x̄, ȳ).

• The sign of b is the same as the sign of the correlation coefficient r.
• A positive correlation gives a positive slope, and a negative correlation gives a negative slope.