The inclusion of 'then-test' questions in post-test questionnaires alters post-test responses: a randomized study of bias in health program evaluation

Qual Life Res. 2012 Apr;21(3):487-94. doi: 10.1007/s11136-011-9952-1. Epub 2011 Jun 28.


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.

Publication types

  • Randomized Controlled Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptation, Psychological
  • Adult
  • Aged
  • Aged, 80 and over
  • Attitude to Health
  • Australia
  • Chronic Disease / psychology*
  • Female
  • Health Status Indicators
  • Humans
  • Male
  • Middle Aged
  • Patient Education as Topic
  • Program Evaluation
  • Psychometrics
  • Quality of Life*
  • Research Design
  • Self Care*
  • Surveys and Questionnaires*