The tendency for people to behave differently when they know they'are being studied is referred to as:

there are treatment options for depression (mdd) that may work for you. one way of treating depression may be to affect the levels of certain chemicals that brain cells use to communicate, called neurotransmitters. scientists believe that certain neurotransmitters may be out of balance in depression.

although the exact way depression medications shown to ease overall depression symptoms in some people work is unknown, scientists think that some medications work by affecting the levels of a neurotransmitter called serotonin in the brain. other treatments work by affecting the levels of other neurotransmitters like norepinephrine or dopamine.

the answer is:

c. economic output