Why people often use one-group posttest-only design if it has a limitation of a lack of pretest?

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The major advantage of the one-group posttest-only design is that it is easier and more time-saving than other quantitative evaluation designs. In some special cases where the participants have similar pre-test status, evaluations under the one-group posttest-only design could produce reliable estimations on whether the program works. Let’s say we provide a program for smokers to help them quit smoking. The participants have the same pre-test status, that is, smoking. We would know whether the intervention makes a difference by measuring the post-test status--whether they still smoke after the intervention.