Researchers in a certain country investigated how having daughters influences voting on women's issues by members of the federal government. The researchers use voting records of each member of the federal government to compute an index score, where higher scores indicate more favorable voting for women's rights. The researchers modeled the index score (y) as a function of the number of daughters (x) a voting member has. Data collected for the 418 members of the federal government last year were used to fit the straight-line model, E(y) = β0 + β1x.
a. If it is true that having daughters influences voting on women's issues, will the sign of β1 be positive or negative? Explain.