Study Questions, Class 4

1. How are the mean and the expected value of a random variable related?

  They are the same thing.

2. What is the formula for the expected value of a discrete distribution?

3. What is the formula for the expected value of a continuous distribution?

4. How do we find the mean of a joint distribution? (Trick question)

  We don't.

5. The mean is a measure of central tendency. The variance is a measure of variability. What is the covariance a measure of?

Linear relationship between two variables. 

6. How are correlation and covariance related?

Correlation is normalized covariance.  

7. Under what condition can we say that E(XY) = E(X)E(Y)?

When X and Y are independent  

8. Under what condition is V(X+Y) = V(X)+V(Y)?

When X and Y are independent  

9. X and Y are independent. What can we say about COV(X, Y)?

  It equals 0

10. COV(X, Y) = 0. What can we say about the independence of X and Y?

  Nothing.

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The following questions are not turned in, but you are encouraged to write out and save the answers in preparation for an exam "cheat sheet".

What is the formula for the variance of a discrete distribution?

What is the formula for the variance of a continuous distribution?

What is the formula for the covariance of discrete distributions?

What is the formula for the covariance of continuous distributions?

What is the formula for the correlation two distributions?