Final answer:
A reversal design should not be used in experimental research when it is unethical or impractical to withdraw the treatment, when the intervention has long-lasting or irreversible effects, or when the behavior being studied shows a carryover effect.
Step-by-step explanation:
A REVERSAL DESIGN (ABAB) should not be used in experimental research when it is unethical or impractical to withdraw the treatment or intervention being tested. For example, if the treatment being studied is a life-saving medication, it would be unethical to remove it from participants. Additionally, a reversal design may not be suitable if the intervention has long-lasting or irreversible effects, making it impossible to return to the baseline condition. Lastly, if the behavior being studied is likely to have a carryover effect that persists even when the treatment is removed, a reversal design may not be appropriate.