In a graph of single-subject research data, a clear indication of a treatment effect is a. a continuation of the same average level from one phase to the next. b. a continuation of a clear trend from...

In a graph of single-subject research data, a clear indication of a treatment effect is

a. a continuation of the same average level from one phase to the next.

b. a continuation of a clear trend from one phase to the next.

c. a gradual change in behavior that becomes clear several observations after the treatment is initiated.

d. a clear and immediate change in either the level or trend when the treatment is initiated.