Blalock, Hubert M. <br/><br/>
Causal inferences in noneexperimental research. 

 - Chapel Hill :  University of North Carolina Press,  [1964] 
<br/><br/>Includes bibliographies. 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Social sciences -- Mathematical models.--Social sciences -- Mathematical models.