Question

Suppose you wanted to compare students in two different classes, assessing whether research methods or social psychology leads to more favorable ratings of how interesting psychology is.

Why would it be important to consider selection, attrition, and history?

Answer 1

Selection

• In an experiment, selection as a threat to internal validity refers to differences in characteristics and attributes in participants in a group or between the groups. Thus the differences in the scores of independent group (manipulated group) and control group can be due to the already exiting differences, rather than due to the interventions.

• For example, I want to study the effect of meditation (intervention) in reducing anxiety among college students, divided in two groups, anxious students (independent group) and Not anxious students (control group). The results indicated decrease in anxiety among anxious student group. Suppose this could be due to the reason that, student who scored less in anxiety in independent group, are not anxious in general, but are anxious in different specific situations.

• Therefore to due reduce this threat, inclusion criteria of participants must be defined in an experiment.

History

• History is also a threat to internal validity, as it refers to sudden and unexpected events, which occurs during the study, and can be responsible for alternative solution.

• For example, Suppose you wanted to compare students in two different classes, assessing whether research methods or social psychology leads to more favorable ratings of how interesting psychology is. Suppose, during this research, riots or massacre occur at some part of country, leading to discussion of causes of this event among general population, like mob behavior, religious identity, group identity, conformity, aggression, etc. Thus, this large scale event can lead students to choose social psychology, in making psychology interesting and to study more about human behavior.

Attrition

• Attrition happens, when respondents of a research group leave during the study. This could result in biased results.

• For example, during comparing students in two different classes, assessing whether research methods or social psychology leads to more favorable ratings of how interesting psychology is, some students change the school, or become absent (due to illness), or their families get transferred. This would result in biased results, and it does not provide the effectiveness of proposed intervention in a group and does not explains the accuracy of obtained results.