13.1 The Correlation Coefficient r

In order to have a correlation coefficient between traits A and B, it is necessary to have:

1. one group of subjects, some of whom possess characteristics of trait A, the remainder possessing those of trait B
2. measures of trait A on one group of subjects and of trait B on another group
3. two groups of subjects, one which could be classified as A or not A, the other as B or not B
4. two groups of subjects…

Define the Correlation Coefficient and give a unique example of its use.

If the correlation between age of an auto and money spent for repairs is +.90

1. 81% of the variation in the money spent for repairs is explained by the age of the auto
2. 81% of money spent for repairs is unexplained by the age of the auto
3. 90% of the money spent for repairs is explained by the age of the auto
4. none of the above

Suppose that college grade-point average and verbal portion of an IQ test had a correlation of .40. What percentage of the variance do these two have in common?

1. 20
2. 16
3. 40
4. 80

True or false? If false, explain why: The coefficient of determination can have values between -1 and +1.

True or False: Whenever r is calculated on the basis of a sample, the value which we obtain for r is only an estimate of the true correlation coefficient which we would obtain if we calculated it for the entire population.

Under a "scatter diagram" there is a notation that the coefficient of correlation is .10. What does this mean?

1. plus and minus 10% from the means includes about 68% of the cases
2. one-tenth of the variance of one variable is shared with the other variable
3. one-tenth of one variable is caused by the other variable
4. on a scale from -1 to +1, the degree of linear relationship between the two variabl…

The correlation coefficient for X and Y is known to be zero. We then can conclude that:

1. X and Y have standard distributions
2. the variances of X and Y are equal
3. there exists no relationship between X and Y
4. there exists no linear relationship between X and Y
5. none of these

What would you guess the value of the correlation coefficient to be for the pair of variables: "number of man-hours worked" and "number of units of work completed"?

1. Approximately 0.9
2. Approximately 0.4
3. Approximately 0.0
4. Approximately -0.4
5. Approximately -0.9

In a given group, the correlation between height measured in feet and weight measured in pounds is +.68. Which of the following would alter the value of r?

1. height is expressed centimeters.
2. weight is expressed in Kilograms.
3. both of the above will affect r.
4. neither of the above changes will affect r.