Final answer:
Quasi-experimental design is used when a single group is exposed to continuous treatment and withdrawal in a time series study to assess the effect of an intervention over time.
Step-by-step explanation:
The type of design that involves a single group with continuous treatment and withdrawal in a time series study is known as a quasi-experimental design. This design does not involve random assignment to control and treatment groups like a controlled experiment, but it does involve manipulation of the independent variable. In such a study, the researcher applies an intervention (the treatment) to observe its effect over time and then withdraws it to see if the observed effects are reversed. This allows the researcher to measure the changes in the dependent variable both during and after the intervention, which can provide evidence for causation in the absence of a true experimental design.