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More on Equation of the Regression Line and Residuals

Example: The following data represent the gestation period of various animals along with their life expectancy.

Enter the predictor variable values into L1 and the response variable values into L2. Press STAT. Highligh CALC, select 4:LinReg(ax+b), press ENTER. Press VARS, highlight Y-VARS, select 1:Function, press ENTER and select 1:Y1 and press ENTER.

Press ENTER.

(a.) Using a and b from the output display, the resulting equation is y = .0261x + 7.8738. Press Y= to confirm that the regression equation has been stored in Y1. Press ZOOM and 9 for ZoomStat and a graph of the scatter plot with the regression line will be displayed.

(c.) Next, you can use the regression equation to predict life expectancy for various animals. For example, to predict the life expectancy for an animal with a gestation period of 95 days, press VARS, highlight Y-VARS. Select 1:Function and press ENTER. Select 1:Y1 and press ENTER. Press ( 95 ) and ENTER.

The predicted life expectancy for this species (with a gestation period of 95 days) is 10.35 years.

(d.) To predict the life expectancy of a parakeet, press 2^nd , found above the ENTER key). Move the cursor so that it is flashin on ‘9’ in the number ‘95’ and type in 18. Press ENTER.

The predicted life expectancy of a parakeet is 8.34 years.

(c.) Press 2^nd . Move the cursor so that is flashing on ‘1’ in the number ‘18’ and type in 68. Press ENTER.

The predicted life expectancy of a guinea pig is 9.64 years.

(f.) Residual= Actual Life Expectancy of a guinea pig – predicted life expectancy of a guinea pig: .