Key points are not available for this paper at this time.
This chapter is a report from a project, Causal Models in Social Research, supported by NSF Grant GS-2707. J. Michael Coble was in charge of computer programing and Eugene Won assisted with the statistical work. Several of the models discu,ssed in the chapter were; suggested by remarks of Donald T. Campbell and David A. Kenny in informal communications, although they are not responsible for the use made of their suggestions.
Otis Dudley Duncan (Sat,) studied this question.