Match List – I with List – II.

List – I (Threats to Internal Validity)	List – II (Description)
A. Maturation threat	I. When participants’ behavior changes as a function of having been tested previously
B. Attrition threat	II. When some event outside the research project affects participants systematically
C. History threat	III. Occurs because of short- or long-term changes in a participant because of psychological changes like boredom, fatigue etc.
D. Testing threat	IV. When participants drop out of a study, leading to a change in the nature of the sample

Choose the correct answer from the options given below:

The correct option is A-III, B-IV, C-II, D-I.

In research design, internal validity refers to the degree of confidence that the causal relationship being tested is trustworthy and not influenced by other factors or variables. The threats to internal validity listed in the question can be defined as follows:

1. A. Maturation threat (matches with III): This threat occurs when physical or psychological changes in the participants over time affect the study's results. These can be short-term changes (like fatigue, boredom, or hunger) or long-term changes (like growing older or wiser). Hence, it matches description III: "Occurs because of short- or long-term changes in a participant because of psychological changes like boredom, fatigue etc."

2. B. Attrition threat (matches with IV): Also known as mortality, this threat happens when participants drop out or leave a study systematically before it is completed, which changes the composition of the sample and can bias the final results. Hence, it matches description IV: "When participants drop out of a study, leading to a change in the nature of the sample."

3. C. History threat (matches with II): This threat refers to external, unplanned events occurring outside the research environment during the course of the study that systematically influence the participants' responses or behavior. Hence, it matches description II: "When some event outside the research project affects participants systematically."

4. D. Testing threat (matches with I): This threat occurs when the act of taking a pre-test or being tested multiple times influences the participants' performance or behavior on subsequent tests (due to familiarity, practice, or memory). Hence, it matches description I: "When participants’ behavior changes as a function of having been tested previously."

By matching each threat with its correct description, we obtain the combination:
A-III, B-IV, C-II, D-I.