DrWisgoski Asks Fifty Drug Addicts a Series of Questions About

Dr.Wisgoski asks fifty drug addicts a series of questions about their childhoods and then collects blood samples from them.He finds a high correlation between levels of the stress hormone cortisol and the amount of reported childhood trauma.Dr.Wisgoski concludes that childhood trauma causes high levels of stress during adulthood,which,in turn,causes drug addiction.Dr.Wisgoski's operational definition of adult stress level is ____.

A) childhood trauma
B) blood cortisol
C) drug addiction
D) self-report