If the same individual participates in both study and experimental group (patient serves as his or her own control), it is called:
**Core Concept**
In clinical research, an individual who participates in both the study group and the control group is known as their own control. This design is used to minimize confounding variables and provide a more accurate comparison between the two groups.
**Why the Correct Answer is Right**
The concept of using the same individual as their own control is based on the principle of internal validity. By having the same participant in both groups, researchers can control for individual differences and focus on the effect of the intervention. This design is particularly useful in cases where a large number of participants are not available or when the intervention is expensive or difficult to administer. The use of internal controls also helps to reduce the risk of bias and increases the reliability of the results.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a crossover design involves participants switching between groups, but it does not involve the same individual serving as their own control in both groups.
**Option B:** This option is incorrect because a matched pairs design involves pairing participants with similar characteristics, but it does not involve the same individual serving as their own control.
**Option C:** This option is incorrect because a randomized controlled trial (RCT) involves randomly assigning participants to either the study group or the control group, but it does not involve the same individual serving as their own control.
**Clinical Pearl / High-Yield Fact**
When designing a study, researchers should carefully consider the use of internal controls to increase the validity and reliability of the results.
**Correct Answer: C. Cross-over design.