Behavioral spillover
Also known as: Behavioural spillover
When one behavior change spreads to other related behaviors — sometimes reinforcing, sometimes undermining the goal.
What it means
Behavioral spillover occurs when adopting one behavior influences the likelihood of performing other, related behaviors, beyond the one directly targeted. Positive spillover (a 'catalyst' or 'gateway' effect) happens when one change promotes consistent further changes — starting to recycle leading to other green habits — often via identity ('I'm an environmentalist now') or learning. Negative spillover, including moral licensing and the rebound effect, happens when one good act gives psychological or material permission to do worse elsewhere ('I biked today, so I'll take a long flight guilt-free'). Which direction dominates depends on how people construe the link between behaviors and whether motivation is identity-based or compensatory. The phenomenon complicates evaluation, since measuring only the target behavior can miss effects — good or bad — that ripple outward. It matters because interventions aimed at a single behavior can quietly help or sabotage the broader goal, and designers can deliberately frame changes to encourage positive spillover.
What the evidence shows
The largest test to date is Maki and colleagues' 2019 meta-analysis, which pooled 77 effect sizes from 22 studies. The headline is sobering. Spillover onto a second behavior was positive but tiny for stated intentions (about d = 0.17) and essentially zero, even slightly negative, for measured behavior (d = -0.03) and policy support (d = -0.01). Doing one green thing nudges what people say they will do next, but barely moves what they actually do. Earlier narrative reviews had already called the evidence mixed, and longitudinal work such as Thogersen and Olander's Danish panel found both catalyst and crowding-out links between recycling, organic food, and transport. Positive spillover is real but small and fragile, not a dependable multiplier you can bank on.
What tips the direction
Whether spillover helps or hurts turns on how the first act is interpreted. Truelove and colleagues' framework distinguishes decision modes: an act read through identity or a social role, this is the kind of person I am, tends to promote further action, while an act read as a cost already paid, or as proof of virtue, invites compensation and licensing instead. Two moderators recur in the data. Similarity: spillover is likelier between behaviors people see as related, recycling to composting, not recycling to flying. Motivation: interventions that engage intrinsic reasons produce more positive spillover than those leaning on money or convenience, which can frame the behavior as a transaction that ends the moment the incentive stops. Framing, not the behavior itself, often decides the sign.
Beyond the environment
Although most studies are environmental, the logic is general. Dolan and Galizzi sort spillovers into promoting, where a first act pulls a second the same way; permitting, where a good act licenses an opposing one (I ran, so I deserve the cake); and purging, where a lapse triggers a corrective act (I was lazy today, best eat light). Their own experiment found that paying people to exercise raised later calorie intake, eroding part of the health benefit, a permitting spillover across the effort-and-reward boundary. Comparable patterns surface in finance and safety, where insurance or protective equipment can invite the very risks it guards against. The policy lesson is that the unit of analysis should be the linked sequence of behaviors, not any single one measured on its own.
Why it is hard to measure
Much of the apparent disagreement is methodological. Galizzi and Whitmarsh, reviewing how spillover is studied, note that many designs cannot separate a true causal ripple from people who were simply consistent to begin with, and that self-reported intentions inflate positive spillover while behavioral measures deflate it, exactly the gap the meta-analysis found. Clean identification needs a randomized first behavior, a genuine control group, and a secondary behavior observed unobtrusively rather than asked about. Because a null or negative result is less publishable than a catalyst story, the literature probably tilts optimistic. In practice, treat any single striking finding with caution, weight the pooled behavior-based estimates over intention measures, and always instrument the non-targeted behaviors you might be quietly helping or harming.
Examples
Households that installed efficient appliances sometimes used them more (negative rebound spillover), eroding the energy savings the intervention was meant to deliver.
Someone who walked to work orders a taxi home and the larger dessert, feeling the virtuous morning has bought them the evening — one good act quietly licensing the bad one.
People who start carrying a reusable cup often go on to refuse straws and bags, not because coffee lids matter much, but because they now see themselves as someone who does this.
Someone who starts keeping a tidy desk often begins clearing their inbox and filing documents as they go, not because one habit requires the others, but because they now see themselves as an organized person.
After automating a monthly pension contribution, some savers ease off other saving, treating the single deduction as proof they are now covered, a compensation that quietly offsets the intended gain.
First described in Thøgersen; Truelove et al. (2014).
Key references
- Maki, A., Carrico, A. R., Raimi, K. T., Truelove, H. B., Araujo, B., & Yeung, K. L. (2019). Meta-analysis of pro-environmental behaviour spillover. Nature Sustainability, 2(4), 307-315. doi.org/10.1038/s41893-019-0263-9
- Galizzi, M. M., & Whitmarsh, L. (2019). How to measure behavioral spillovers: A methodological review and checklist. Frontiers in Psychology, 10, 342. doi.org/10.3389/fpsyg.2019.00342
- Nilsson, A., Bergquist, M., & Schultz, W. P. (2017). Spillover effects in environmental behaviors, across time and context: A review and research agenda. Environmental Education Research, 23(4), 573-589. doi.org/10.1080/13504622.2016.1250148
- Dolan, P., & Galizzi, M. M. (2015). Like ripples on a pond: Behavioral spillovers and their implications for research and policy. Journal of Economic Psychology, 47, 1-16. doi.org/10.1016/j.joep.2014.12.003
- Truelove, H. B., Carrico, A. R., Weber, E. U., Raimi, K. T., & Vandenbergh, M. P. (2014). Positive and negative spillover of pro-environmental behavior: An integrative review and theoretical framework. Global Environmental Change, 29, 127-138. doi.org/10.1016/j.gloenvcha.2014.09.004
- Thogersen, J., & Olander, F. (2003). Spillover of environment-friendly consumer behaviour. Journal of Environmental Psychology, 23(3), 225-236. doi.org/10.1016/S0272-4944(03)00018-5