When the Fed conducts an open market sale, it leads to a higher level of investment and output in the economy

A causal effect for a single individual

A) can be deduced from the average treatment effect. B) cannot be measured. C) depends on observable variables only. D) is observable since it is used as part of calculating the mean of individual causal effects.

Firms exist because of

A) incomplete contracts. B) team production. C) the incentive to free ride. D) all of these choices.