If he wants to carry out a sociological study, the step thats most threatening to the integrity of his studyis using his common sense whenever he is unable to ask or observe. The main characteristics of a scientific investigation are: to be programmed, carried out with valid methods and instruments, that offers new knowledge, that is objective, responds to the scientific method, offers comprehensible results, that is verifiable and allows the elaboration of theories. The use of common sense because of lack of data would be rejected outright by the scientific community.