Related Experiment Video
Updated: May 31, 2026

Validation of a Psychosocial Intervention on Body Image in Older People: An Experimental Design
Published on: May 31, 2021
The inclusion of 'then-test' questions in post-test questionnaires alters post-test responses: a randomized study of
Sandra Nolte1, Gerald R Elsworth, Andrew J Sinclair
1Deakin University, Burwood, VIC, Australia. sandra.nolte@web.de
Objectives:
Program evaluations are frequently based on 'then-test' data, i.e., pre-test collected in retrospect. While the application of the then-test has practical advantages, little is known about the validity of then-test data. Because of the collection of then-test in close proximity to post-test questions, this study was aimed at exploring whether the presence of then-test questions in post-test questionnaires influenced subjects' responses to post-test.
Patients And Methods:
To test the influence of then-test questions, we designed a randomized three-group study in the context of chronic disease self-management programs. Interventions had comparable goals and philosophies, and all 949 study participants filled out identical Health Education Impact Questionnaires (heiQ) at pre-test. At post-test, participants were then randomized to one of the following three groups: Group A responded to post-test questions only (n = 331); Group B filled out transition questions in addition to post-test (n = 304); and Group C filled out then-test questions in addition to post-test (n = 314).
Results:
Significant post-test differences were found in six of eight heiQ scales, with respondents who filled out then-test questions reporting significantly higher post-test scores than respondents of the other groups.
Conclusions:
This study provides evidence that the inclusion of then-test questions alters post-test responses, suggesting that change scores based on then-test data be interpreted with care.
Related Concept Videos
Cochran's Q Test
Blind Procedures
Blinding
What is an Experiment?
Bias
In statistics, a sampling bias is created when a sample is collected from a population, and some members of the population are not as likely to be chosen as others (remember, each member...
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
