Review Vocabulary

Correlation A measure of the direction and strength of the straight-line relationship between two quantitative variables. Correlations take values between -1 and 1, with the same sign as the regression line slope. (p. 254)

Explanatory variable A variable that attempts to justify the observed outcomes. (p. 242)

Extrapolation The use of the regression equation to predict for values of outside the range of values in the data used to fit the line. (p. 270)

Interpolation The use of the regression equation to predict for values of that lie inside the range of values in the data used to fit the line. (p. 270)

Least-squares regression line A line drawn on a scatterplot that makes the sum of the squares of the vertical distances of the data points from the line as small as possible. The regression line can be used to predict the response variable for a given value of the explanatory variable . (p. 262)

Negative association Two variables have negative association if an increase in one variable tends to accompany a decrease in the other variable. The scatterplot has a northwest-to-southeast pattern, and the regression slope and correlation are both negative. (p. 247)

Outlier A point in a scatterplot that lies outside the overall pattern of the other points. Outliers sometimes strongly influence the value of the correlation and the position of the least-squares regression line. (p. 245)

Positive association Two quantitative variables have positive association if an increase in one variable tends to accompany an increase in the other variable. The scatterplot has a southwest-to-northeast pattern, and the regression slope and correlation are both positive. (p. 247)

Regression line Any line that describes how a response variable changes as we change an explanatory variable . The most common such line is the least-squares regression line. (p. 251)

Response variable A variable that measures an outcome of a study. (p. 242)

Scatterplot A graph made by plotting ordered pairs of data to show the relationship between two quantitative variables. (p. 242)

Slope of a line The change in the vertical (y) direction along the line when we move 1 unit to the right in the horizontal (x) direction. (p. 253)

y-intercept of a line The vertical (y) coordinate of the point on the line corresponding to 0 on the horizontal (x) axis. (p. 253)