The Pearson correlation between X1 and Y is r = 0.40 and SSY = 100. When a second variable, X2, is added to the regression equation, we obtain R2 = 0.25. How much additional variability is contributed by adding the second variable as a predictor compared to using X1 alone?

A strong correlation exists between stressful life events and the onset of depression, but it is difficult to interpret this relationship because

a. there haven't been enough studies. b. stress can cause depression, but depression can cause stress. c. depression is a very subjective state and thus very difficult to measure. d. people are usually aware of any connection between their depression and stress in their lives.

All facets of both intelligence and memory decline during middle age.

a. true b. false