difference between census and sampling method
census: include all the items of the universe.time consuming. more expensive. large battery of trainded investigators needed so only big reseach org. can perform it. less reliable when not conducted properly. cross check difficult. more errors.
sampling: include a part of items of the whole universe. time saving. less expensive. less battery of trained investigators needed so small org. can also conduct it. more realiable when conducted in a scientific manner. cross check possible. less errors.