3) A study, published in 1995, investigated the use of marijuana and other drugs

Question

3) A study, published in 1995, investigated the use of marijuana and other drugs. Data from 11 countries are summarized in the regression analysis below. The data showed an association between the percentage of a country's ninth graders who report having smoked marijuana and who have used other drugs such as LSD, amphetamines, and cocaine. Variable Coefficient SE Coefratio P-value a) Use the regression output at left to write an equation for the LSRL predicting other Intercept Marijuana 3.06780 2.204 1.39 0.1974 drug use from marijuana use 0.615003 0.0784 7.85

Explanation / Answer

a) The regression equation can be written as

Percentage of country's ninth graders who used other drugs = -3.0678 + 0.615003*Percentage of country's ninth graders who smoked marijuana

b) S is called the Standard Error or the Standard Error of the Estimate (i.e predicted value of percentage of country's ninth graders who used other drugs using the above regression equation with predictor as Percentage of country's ninth graders who smoked marijuana).

S is the average squared difference of the error in the actual to the predicted values of the date (i.e. the square root of the mean squared error). The smaller the value of S, the stronger the linear relationship.

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