Discussion
lung cancer
EXPOSURE TO RADON, SAID, LUNG CANCER
Exposure to radon – and the associated risk of lung cancer – is increasing in multiple countriesThe effect of combining interventions in this way was large. We observed an almost 50% (11%-point) increase in test uptake among those who received a BI letter, bringing the uptake rate to roughly 1-in-3. This effect is much larger than previous radon testing trialsWhile the strength of the effect for policymakers is encouraging, identifying the mechanism underlying it is not straightforward. The effect could have been driven by one feature (e.g., merely simplifying the text), two features (e.g., simplification and using numeric frequencies), three features, or all features (simplification, numeric frequencies, reciprocity, endowment and urgency). It’s also possible that one or more features had a negative effect, and the effect size of combining fewer features would have been even larger. Given the size of the five-feature effect relative to other interventions in the literature, however, we think this possibility is unlikely. Timmons et al. (2022) similarly observed large effect sizes from a ‘behavioural package’ interventions, relative to the standard approach of testing just oneThat said, the results also point to the importance of individual tests of interventions that have greater costs (e.g., designing and printing new envelopes). We recorded no additional benefit of posting our BI letter in a redesigned envelope, despite the positive effects of such envelope manipulations in other studiesMoreover, while uptake rate remained 17% (4%-points) above the control letter when the printed map was included, this represents a reduction in uptake relative to the effectiveness of the BI letter alone. Other trials that have tested additional material with a letter have shown small positive effects on tax compliance (e.g., a flyer used by Hoy, McKenzie and Sinning, 2023It is worth dwelling on possible counterfactual experimental designs. Had we tested just one treatment that combined all interventions, we would have observed a relatively large effect, but for an intervention with greater resource costs for less benefit than merely adapting the letter. Note also that the response observation time had important implications for our assessment of the trial. Those who received the map responded significantly faster than other groups and, had we limited our observation period to just the first 2 weeks, we may have erroneously concluded superiority of this intervention.Limitations of the trial present opportunities for future research. We recorded test uptake using a pre-existing system that required householders to return (via free post) forms to receive the test kits. Reducing frictions in the test kit ordering system, for example by implementing online applications, may lead to stronger effects. Moreover, there is scope to test interventions to improve downstream behaviours, such as test kit returns and, importantly, remediation rates among those who receive high radon readings as there is no health benefit associated with radon testing unless it leads to remediation. There is presently little research available to inform remediation behaviour trialsMore broadly, our results demonstrate the benefit of using the psychology of risk perception and behavioural science to inform radon communications with householders. By doing so, we have demonstrated effective techniques for increasing testing rates for a substantial health hazard, thereby increasing the likelihood of householders remediating against the carcinogenic gas. The strength of the positive result we observe supports recent calls from experts for theoretically informed communications with householders that are evaluated using rigorous methods