Proportion of total variation is accounted for by explained variation

[scolty]

Hi, I've come across a question in a stats book which asks the following:

Q: A study was undertaken to find the relationship between "emotional stability" and performance in college. The following results were obtained:
Emotional stability, Mean = 49, Standard Dev = 12
College Average, Mean = 1.35, Standard Dev = 0.5
pearson r = 0.5
n = 60

What proportion of total variation is accounted for by explained variation?

As far as i was aware, i need to know the actual values in order to be able to calculate this (ie summation of (Yprime - Ymean)^2) but the above info is the only supplied information. Have i missed something? If so id appreciate it if someone could point it out. Thanks.

 

[SW VandeCarr]

Hi, I've come across a question in a stats book which asks the following:

Q: A study was undertaken to find the relationship between "emotional stability" and performance in college. The following results were obtained:
Emotional stability, Mean = 49, Standard Dev = 12
College Average, Mean = 1.35, Standard Dev = 0.5
pearson r = 0.5
n = 60

What proportion of total variation is accounted for by explained variation?

As far as i was aware, i need to know the actual values in order to be able to calculate this (ie summation of (Yprime - Ymean)^2) but the above info is the only supplied information. Have i missed something? If so id appreciate it if someone could point it out. Thanks.

Partitioning total variance among different sources is accomplished by Analysis of Variance (ANOVA) methods. In your case, there is only one named predictor variable, so you would partition the total variance between "emotional stability" and "other". ANOVA also compares variance within groups with variance between groups.

http://www.sjsu.edu/faculty/gerstman/StatPrimer/anova-a.pdf

 

[Stephen Tashi]

As far as i was aware, i need to know the actual values in order to be able to calculate this (ie summation of (Yprime - Ymean)^2) but the above info is the only supplied information. Have i missed something? If so id appreciate it if someone could point it out. Thanks.

The Wikipedia currently has an interesting article on "explained variation" and mentions that some people consider it to be the square roof of the correlation coefficient. You could find the correlation coefficients since you know r.

I don't think you'll make any progress trying to use ANOVA calculations on the given information since you don't know have any information about the subjects being divided into groups.

 

[ssd]

100r^2 is the %-age of total variance explained by linear regression.