Dr. Finkel is a social psychologist who studies romantic relationships. Several researchers have found that there is a link between income and marital satisfaction. Dr. Finkel is curious as to whether there is a causal link between the two variables, such that having a higher income causes higher levels of marital satisfaction. He is confident that he cannot reasonably or ethically manipulate people's income level, so he decides to use a multivariate design. He is also curious as to whether there is a causal link between these two variables or if two other variables (number of arguments and life satisfaction) can explain the relationship. He measures his variables in a sample of 124 married couples recruited from a local community center. DV: Martial Satisfaction
Variable Beta (β) Significance (p)
Income 0.73 0.03
Number of argument -0.69 0.01
Life satisfaction 0.13 0.81

Which of the following is NOT a predictor variable in Dr. Finkel's study?

a. As the number of arguments a couple has increases, their marital satisfaction decreases, when controlling for income and life satisfaction.
b. The relationship between marital satisfaction and life satisfaction has the weakest effect size.
c. The beta for the relationship between marital satisfaction and life satisfaction is statistically significant.
d. All of these can be concluded