Report before-and-after differences among followed participants accurately
A fictional example for illustration: aggregate the 15 of 20 consultation recipients who answered the same questions at start and completion.
| Aggregation | At start | At completion | Interpretation |
|---|---|---|---|
| Mean score for the same 15 people | 2.4 points | 3.1 points | Mean increase of 0.7 points among the same 15 |
| 5 people not followed up | Initial records available | No response | Change unknown |
| Study conditions | Same 5-point question | Same wording and response method | Changes in participants' self-assessments |
What this example supports
Do not report the 15 people's differences as change for all 20. Avoid treating higher self-assessment as actual behavioral change or causal program effects.
Common errors in judgment
Treat means for 20 at start and 15 at completion as within-person change
How to revise: Separate matched-person analysis from aggregation of all respondents at each timepoint
Reason: Changes in respondent composition affect mean differences.
Improve question wording only at completion
How to revise: Where possible, test change effects and report differences in comparison conditions
Reason: This avoids confusing changes in instruments with changes in people.
Put it into practice next
Use the descriptive statistics worksheet to organize initial and final participant breakdowns and summaries
Frequently asked questions
Is a baseline survey always required before the program starts?
Pre-start data are easiest to compare, but existing administrative statistics, usage records or previous studies may substitute. Check their definitions and limitations.
When should an endline survey occur?
Align with when outcomes of interest arise. Consider delays, such as knowledge immediately after training, behavior after several months and conditions later still.
What if the same people cannot be followed?
Group comparisons at start and end are possible but cannot be read as individual change. Align target characteristics and interpret after checking differences in respondent composition.
References and checked sections
- Glossary of Key Terms in Evaluation and Results-Based Management for Sustainable Development (Second Edition)OECD · 2023
- Section consulted
- Baseline / Baseline study (main text, p.21) / End line (main text, p.30)
- How it relates to the text
- A basis for comparing pre-start and final conditions
- Best Practices for Survey ResearchAmerican Association for Public Opinion Research
- Section consulted
- Planning Your Survey / How can I measure change over time? / What kinds of testing should I do before fielding a survey? / Analyzing and reporting the survey results
- How it relates to the text
- Questions fitting evaluation questions, consistent measurement conditions, pretesting, non-response and transparent reporting
- Is My NGO Having a Positive Impact?David Evans / Bruce Wydick(World Bank Development Impact) · 2016
- Section consulted
- Before and After / Beneficiaries and non-beneficiaries
- How it relates to the text
- Differences between NGO outcome measurement and causal effects, and limitations of before-and-after and participant/non-participant comparisons
How to cite this page
Change history
- — Distinguished original methodological sources from practical guidance and added specific fictional examples, judgment examples and next actions. Revised categorical claims about classification and measurement conditions.







