Question

You know that there is a strong correlation between the consumption of ice cream and body weight. The Pearson's r = 0.78. You also know that the average consumption of ice cream per week is five grams with a standard deviation of 1.5 grams. The average weight is 65 kg with a standard deviation of 15 kg. What is the formula of the regression line?

Answer 1

y = 7.8x + 26

Explanation:

Given the following :

Pearson's r = 0.78

Average consumption of ice cream = 5 grams per week (m) with Standard deviation (sd) = 1.5 grams

Average weight = 65 kg with standard deviation of 15kg

Formular for the regression line :

General regression formula :

y = mx + c

y = predicted variable ; m = slope or gradient ; x = predictor variable ; c = intercept

Gradient (m) = change in y / change in x

m = (sd y / sd x) * r

m = (sd weight / sd ice cream) × r

m = (15 / 1.5) × r

m = 10 × 0.78 = 7.8

Intercept:

mean of weight(y) - [Slope×mean of icecream(x)]

65 - [7.8 × 5]

65 - 39 = 26

Hence,

y = 7.8x + 26