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 answer is A-III, B-IV, C-II, D-I.

To understand why, let us carefully analyze each threat to internal validity listed in List – I and match it with the most accurate description from List – II.

A. Maturation Threat → III
The maturation threat refers to changes that occur within the participants themselves over the course of a study — not because of the treatment or intervention, but simply due to the passage of time. These changes can be biological (growing older, getting tired) or psychological (becoming bored, losing motivation, developing fatigue). Description III perfectly captures this: "Occurs because of short- or long-term changes in a participant because of psychological changes like boredom, fatigue etc." If participants feel fatigued or bored between pre-test and post-test, any observed change in their scores may be due to this internal maturation rather than the study's treatment.

B. Attrition Threat → IV
The attrition threat (also called mortality threat) arises when participants drop out of a study before it is completed. This is dangerous because the remaining sample may be systematically different from the original sample — for example, only the most motivated participants may stay, skewing results. Description IV states: "When participants drop out of a study, leading to a change in the nature of the sample." This is an exact match. The word "attrition" itself means a gradual reduction in numbers, which aligns perfectly.

C. History Threat → II
The history threat occurs when some external event — outside the researcher's control and outside the research project itself — affects participants between measurements. For example, if a nationwide economic crisis occurs during a longitudinal study on stress, that event (not the study's intervention) could change participants' responses. Description II captures this precisely: "When some event outside the research project affects participants systematically." The key word here is "outside" — the threat originates in the real world, not within the study design.

D. Testing Threat → I
The testing threat (also called the test-retest effect) occurs because participants have been tested previously. Simply being exposed to a test once changes how a participant responds to the same or a similar test later — they may remember questions, develop test-taking strategies, or feel more comfortable. This has nothing to do with the actual treatment being studied. Description I matches perfectly: "When participants' behavior changes as a function of having been tested previously." The phrase "having been tested previously" is the defining characteristic of the testing threat.

Summary Table:

Therefore, the correct matching is A-III, B-IV, C-II, D-I.