The effect of a treatment in a simple interrupted time-series design is best indicated by
A) an increasing trend in the dependent variable that is present both before and after the treatment.
B) a decreasing trend in the dependent variable that is present both before and after the treatment.
C) a clear discontinuity (abrupt increase or decrease) in the dependent variable at the point the treatment is administered.
D) a gradual change in the dependent variable that begins just as the treatment is implemented.

Question

Quizplus · Accepted Answer

In a simple interrupted time-series design, the effect of a treatment is best indicated by a clear discontinuity (abrupt increase or decrease) in the dependent variable at the point the treatment is administered. This suggests that the treatment had an immediate impact on the outcome being measured. It is important to establish a stable baseline trend before the treatment and to have multiple data points after the treatment to ensure that the observed change is not due to other factors. A gradual change (D) may also indicate an effect, but it is less clear and may be confounded by other factors. Increasing (A) or decreasing (B) trends may indicate overall changes in the outcome but do not necessarily reflect the effect of the treatment specifically.

The Effect of a Treatment in a Simple Interrupted Time-Series