Following are some possible relationships that we might find in observational data that come, say, from a national random sample survey of US adults: a. computer skills earnings b. exercise diabetes c. marital status happiness given that these simple relationships came from observational data, and that we are interested in getting the true causal effects suggested by the arrows, what control variables would we need? Think about likely common causes of both variables and be careful not to pick intervening variables. list the control variables with their operational definitions and then explain