History threat to internal validity – UGC NET Question

The history threat to internal validity arises when events outside the experiment, such as policy changes or natural disasters, occur between measurements and influence participants’ responses. These events are not part of the planned treatment but can mimic or obscure treatment effects. If not controlled, they make it difficult to attribute changes solely to the intervention. Thus, the external event effect described in the stem is known as history.

Option A:
Maturation refers to natural changes within participants over time, such as ageing, fatigue or learning. These are internal to the individuals rather than external events affecting the group. Therefore, maturation is a different threat from the one described.

Option B:
Option B, history, focuses on time-related external events that coincide with the experiment and influence outcomes. For example, a media campaign or institutional change during the study period could create a history effect. Because the stem highlights external events between pre-test and post-test, this option is correct.

Option C:
Testing effects arise when taking a test influences performance on later administrations of the same test, such as through practice or sensitisation. This does not involve outside events, so it does not match the question.

Option D:
Instrumentation refers to changes in measurement instruments or observers over time, which can alter scores independently of the treatment. It is another threat to internal validity but not the one defined in the stem.