Setting the stage for the phenomenal contributions of Carl Hovland, Rockefeller donated the funding necessary to begin the "Institute of Human Relations" at Yale in 1929. Shortly afterwards, in 1936, Hovland secured his Ph.D. from Yale and joins the faculty there. With the US involvement in World War II in 1941, Hovland sees the opportunity to study Army morale and takes a hiatus from his work at Yale.
Hovland is particularly unique and his studies are exceptionally valuable because he was so meticulous in his execution of his experiments. It is not easy to do well designed and well controlled experiments, yet Hovland managed to do just that which is why he is remembered as the founder of Effects Theory.
Through his work with soldiers he was able to have complete control over outside factors and could thus manipulate one component and connect that manipulation to its respective effect. In addition, there could be more than one factor, as in confounding variables, but they to could be built into the design of the experiment.
With the "Why We Fight" series that Hovland created and experimented with (in more than 50 experiments), the soldiers most dramatically learned the information, their attitudes changed regarding the enemy, and they were no more eager to die for their country. Moreover, Hovland took notice of the apparent gap between the effects upon soldiers who were smarter as opposed to those with less education. His conclusions stated that mass communication can teach factual material but the components of the audience will vary the resulting effects -- the message is perceived variably by different audiences.
Once he returned to Yale, Hovland received a $370,000 Rockefeller grant to continue his studies on communication and persuasion. These experiments tested source credibility, one and two-sided messages, channel variables such as face-to-face or media effects, receiver variables like intelligence and gender, fear appeals, inoculation of beliefs, and the 'sleeper effect' where people remember the message but forget the source.
Generally, Hovland found that when a conviction was not strongly held, attitude change was easy to achieve on the short-run. However, the converse is also true that long-term opinion change on topics that are firmly held is difficult to achieve.
Hovland was diagnosed with cancer in 1960 and regrettably took his own life in 1961 by drowning himself in his bathtub.
William McGuire followed Hovland research by examining the "stages of change" in effects. He has concentrated on the continuum across exposure, attention, comprehension, yielding, memory, and behavior.