Poor nutrition, family stress, and memory difficulties have all contributed to Mr. Leonard's depression. Effectively explaining the full complexity of his problems requires.

Biopsychosocial approach is the correct answer.

The biopsychosocial approach effectively explains the full complexity of one's disorder since it requires multiple levels of analysis. Psychologists who adopt the biopsychosocial model focus on examining how and why the problem is occurring by investigating the biological, psychological and social factors that affect the patient. Thus, when we say Mr. Leonard's depression is the result of poor nutrition, family stress, and memory difficulties, we are using the biopsychosocial approach.