1. LEAST – SQUARES REGRESSION
AP STATISTICS LESSON 3 – 3
LEAST – SQUARES REGRESSION

2. Regression Line
A regression line is a straight line that describes how a response variable y changes as an explanatory variable x changes. We often use a regression line to predict the value of y for a given value of x. Regression, unlike correlation, requires we have an explanatory variable and a response variable.
LSRL – Is the abbreviation for least squares regression line. LSRL is a mathematical model.

3. Least – squares Regression Line
Error = observed – predicted
To find the most effective model we must square the errors and sum them to find the least errors squared.

4. Least – squares Regression Line
The least – squares regression line of y on x is the line that makes the sum of the squares of the vertical distances of the data points from the line as small as possible.

5. Equation of the LSRL
We have data on an explanatory variable x and a response variable y for n individuals. From the data, calculate the means x and y and the standard deviations sx and sy, and their correlation r.

6. What happened to y = mx+b?
y represents the observed (actual) values for y, and y represents the predicted values for y. We use y hat in the equation of the regression line to emphasize that the line gives predicted values for any x.
When you are solving regression problems, be sure to distinguish between y and y.
Hot tip: (x, y) is always a point on the regression line! ˆ ˆ