more accurate in direct mail than in newspaper advertising, since the key is fixed to the printed material, but it involves a lot of extra labor.
Another method of tabulating the sources of information about the program is to ask people at the time of registration where they first heard about it. Information obtained in this way is probably the least reliable of all, but it may give some interesting clues that can be checked against other data Usually considerable time has elapsed between the individuals’ first leaning about the program and time of registration, and they will make a guess at how they first heard about it. Several times people have actually brought in clipped ads or news stories that appeared only in one paper, and have maintained that they clipped them from another.