Selection treatment interaction – UGC NET Question

Interaction of selection and treatment occurs when the characteristics of those selected for the study, such as being volunteers or highly motivated individuals, interact with the treatment in such a way that results may not hold for a broader population. This threatens external validity because the findings may not generalise beyond the specific type of participants used. Recognising and minimising such biases is important when designing experiments. Therefore, the threat described in the stem is the interaction of selection and treatment.

Option A:
Selection refers to how participants enter the study and the ways in which they may differ systematically from the target population. When these differences influence how they respond to treatment, generalisation becomes problematic, capturing the idea in the stem and making this option correct.

Option B:
Testing as a threat to validity involves effects of taking a pretest on later performance, not differences between volunteers and non-volunteers. It is more about sensitisation than about participant characteristics.

Option C:
History refers to external events occurring between measurements that affect outcomes for all participants, which is different from the differential response of specific selection groups.

Option D:
Instrumentation concerns changes in measurement tools or observers over time, affecting scores independently of the treatment and is unrelated to how volunteers might differ from non-volunteers in responsiveness.