When is the one-group posttest-only design most suitable to be adopted?

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This design is well-suited as long as the pre-test status is not a concern. For example, when clients’ status before the intervention can be ascertained from previous documents, a formal assessment before the intervention would be unnecessary. Or, in the case that clients’ pre-test status is one of the recruitment criteria, the one-group posttest-only design can also be adopted.