Briefly answer the following questions. 1. Suppose you are interested in estimating the causal effect of class size on pupil?s test scores. You want to estimate the relationship: Y = ? + ?1CSi + ?2Xi + error term Where i indexes individuals, Y denotes an individual?s test score, CS class size, and X a set of control variablesRequirements: a. A regression of actual class size on expected class size (and control variables) yields an estimate on expected class size of 0.335 (with a standard error of 0.051). What does this information tells you about the validity of the research design? b. Separate regression model of parental education and parental income (measured before the children are age 10) on expected class size produce estimates that have t-ratios of ?0.15 (parental education) and 0.08 (parental income). What does this information tells you about the validity of the research design?