Controlling for warm glow in environmental DCE surveys
Warm glow - the moral satisfaction of appearing to support environmental causes - inflates stated WTP in surveys. It must be identified and controlled.
What warm glow is, how it biases environmental DCE responses, and how to reduce its influence.
Knowledge Base -> Survey Building -> Environment
Ben White, 07.07.2026
What is warm glow?
Warm glow is the utility respondents derive from the act of appearing to support a good cause, independent of the actual environmental outcome. A respondent who states high WTP for nature conservation because doing so makes them feel virtuous - rather than because they genuinely value the specific improvement - is exhibiting warm glow bias.
Warm glow inflates WTP estimates and compromises scope sensitivity. If the moral satisfaction from 'supporting conservation' is the same regardless of the scale of the improvement, WTP will be scope-insensitive.
How warm glow manifests in choice experiments
Warm glow cannot be eliminated from stated preference surveys but it can be reduced by survey design. Making the trade-off more concrete, reminding respondents of their budget constraints, and emphasising that the cost is real and mandatory all reduce the influence of warm glow.
Studies that do not address warm glow produce WTP estimates that are not valid for cost-benefit analysis. If the WTP reflects the moral value of 'being a good person' rather than the economic value of the environmental improvement, it cannot be aggregated to estimate total social benefit.
TLDR Quick links
Controlling for warm glow in SurveyEngine
Step 1: Include a budget reminder. Before the choice tasks, ask respondents to consider their household budget and list their major monthly expenditures. This grounds the WTP question in real financial constraints.
Step 2: Emphasise the consequentiality of the survey. Explain that the results will be used to inform real policy decisions. Respondents treat consequential surveys more seriously than perceived research exercises.
Step 3: Use a within-design scope test. Including scope as a varying attribute within the same design identifies warm glow through scope insensitivity.
Step 4: Include a debriefing scale. After the choice tasks, ask respondents to rate their agreement with statements like 'I chose partly because I wanted to support environmental protection in general'. High scores indicate warm glow.
Step 5: Use the debriefing scale in sensitivity analysis. Estimate WTP separately for high and low warm glow scorers. The difference estimates the warm glow bias.
Worked example - biodiversity offsetting WTP
An environmental DCE includes a 4-item debriefing scale measuring warm glow. 31% of respondents score in the top warm glow quartile. WTP estimates for the high warm glow group are 47% higher than for the low warm glow group for the same environmental improvement.
Scope sensitivity is also worse in the high warm glow group - WTP increases by only 12% when scope doubles, compared with 31% in the low warm glow group. Sensitivity analysis reporting both groups alongside the full sample estimate is included in the study report.
References
Kahneman, D. and Knetsch, J.L. (1992). Valuing public goods: the purchase of moral satisfaction. Journal of Environmental Economics and Management, 22(1), 57–70.
Bateman, I.J. et al. (2002). Economic Valuation with Stated Preference Techniques. Edward Elgar.
Designing an environmental valuation DCE? Contact SurveyEngine to discuss warm glow controls and survey framing.
Or Contact us at support@surveyengine.com — we're glad to help.