ON THE BACK / Correlation Practice Questions / Instructor: Kim Barchard
1. Imagine that covariances were calculated in several different studies. Which covariance represents the strongest relationship? (1 mark)
a)-.9
b)-.3
c)0
d).2
e).8
f)answer cannot be determined from the information given.
2.If the covariance between two variables is 3, and the variances of the two variables are each 4, what is the correlation? (2 marks)
3.If the correlation between extraversion and number of books sold is positive for both men and women, what can we say for sure about the correlation when it is calculated on all subjects, regardless of sex? (1 mark)
a)it will be positive
b)it will be negative
c)it will be near zero
d)it will be strong
e)it will be weak
f)nothing can be said for sure
4.The sample correlation is a negatively biased estimate of the population correlation. What does this mean? (2 marks)
5.Usually, if we restrict the range of our two variables, the correlation between them will (1 mark)
a)increase
b)decrease
c)stay about the same
d)reverse its sign
6. Coefficient of determination is
a) r
b) R2
c) percentage of variance accounted for
d) the square root of the standard error of estimate
e) more than one of the above
7.The relationship between college grades and intelligence is likely: (1 mark)
a) no relationship
b) positive relationship
c) negative relationship
d) Pearson correlation coefficient
8.What does a correlation of –1 indicate? (1 mark)
9.Which of the following covariances represents the strongest relationship? (1 mark)
a)-.8
b)-.5
c).0
d).3
e)The answer cannot be determined from the information given
10.In my research on Emotional Intelligence, I examined the correlation between the LEAS and Emotional Expressivity. In a sample of 25 students, I obtained a correlation of .40. Test the null hypothesis that , using a two-tailed test with = .05. Record the critical value for the correlation and state your conclusion (retain or reject). (2 marks)
11.Dr. Barchard is interested in studying the relationship between Agreebleness and academic success. She collects a sample of 3 UNLV students, and obtains the following scores:
Subject / Agreeableness / Grade Point Average1 / 55 / 2.2
2 / 60 / 3.4
3 / 65 / 2.8
Mean / 60 / 2.8
Standard Deviation / 5 / .6
Calculate the covariance and correlation between these two variables. Then, calculate the coefficient of determinination. Show all your work to get partial credit. (4 points)
Covariance______
Correlation______
Coefficient of Determinination______
12.What happens to the sample correlation as alpha increases? (1 point)
- it increases
- it decreases
- it gets closer to the population correlation
- nothing
13.Dr. Barchard conducted an experiment to examine the relationship between Extraversion and grades. She obtained a sample correlation of -.35, using a sample of 32 undergraduates. Test the hypothesis that the population correlation is 0. Use a two-tailed test with alpha = .05.
(5 points)
Ho: ______
H1: ______
df______
r(crit)______
conclusion ______
14.The following scatterplot shows the relationship between Inductive Reasoning and Visualization, for 473 students at the University of British Columbia.
What is the correlation between these two variables? (1 point)
- -.973
- -.522
- -.178
- 0
- .178
- .522
- .973
Examine each of the following statements. For each, indicate if they are true or false. Only mark a statement as true if it is completely true. If some part of the statement is false, mark it false. If the statement is only sometimes true, mark it false. Each statement is worth 1 mark.
15. / Correlations can range from 0 to 1.16. / If one of your variables is positively skewed and the other is negatively skewed, it is impossible to obtain a correlation of 1.
17. / If the relationship between two variables is non-linear, the Pearson Product-Moment Correlation will over-estimate the degree of relationship.
18.Imagine that a researcher is interested in the relation between cooking skill and the number of cooking classes taken. The researcher knows that the correlation is positive for both men and women. What will the correlation be if men and women are combined into one analysis? (1 mark)
a)positive
b)negative
c)zero
d)can’t be determined from the information given
Correlation Practice Exam Questions Answers
1. / f) answer cannot be determined from the information given. (covariances tell you if the relationship is positive or negative, but not how strong the relationship is)2. / standard deviation of X = square root of 4 = 2.
standard deviation of Y = square root of 4 = 2
correlation = 3 / (2*2) = ¾ = .75
3. / f) nothing can be said for sure. (men and women are heterogeneous subgroups)
4. / The sample correlations will underestimate the population correlation, on average.
5. / b) decrease
6 / More than one of the above (it’s both R squared and the proportion of variance accounted for)
7. / b) positive relationship
8. / Perfect negative relationship
9. / e) answer cannot be given (covariances do not tell you the STRENGTH of the relationship)
10. / Critical value = .396; Reject Ho
11. / Covariance = 1.5
Correlation = .5
Coefficient of Determination = .25
12. / Nothing happens to the sample correlation as alpha increases.
13. / Ho: rho = 0
H1: rho does not equal 0
Df = 30
r(crit) = .349
conclusion: Reject Ho
14. / .522
15. / F
16. / T
17. / F
18. / Can’t be determined.