In the Early 20th Century, Many People Displayed Symptoms of a Disorder

Multiple Choice

In the early 20th century, many people displayed symptoms of a disorder similar to organic psychosis.Most of these people were also poor, which led to speculation about class inferiority.Goldberger found correlations between the disorder and diet and identified the cause of the disorder as a deficiency of the B vitamin niacin.What was this research study an early example of?

A) clinical psychology
B) experimental research
C) the case study method
D) epidemiology