In these equations, 5 , and sy are the standard deviations of variables x and y , respectively, while x and y are the means of those two variables. (See the Scientific Skills Exercise for Chapter 32 for more information about the correlation coefficient, mean, and standard deviation.)
The equation for a regression line can be used to calculate the value of y expected for any particular value of x . For example, suppose that a linear regression indicated that m = 2 and b = 4 . In this case, when x = 5 , we expect that y = 2x + 4 = (2 × 5) + 4 = 14 . Based on the values of m and b that you determined in Question 4 , use this approach to determine the expected mean brain volume for a hominin that lived 4 million years ago (that is, x = -4) .