In her new paper, Tatiana Homonoff from Princeton University shows that small incentives can have a larger effect than the simple cost/benefit calculation would suggest, but how these incentives are framed matters. Her findings accord with the idea of loss aversion – that people value losses more than the equivalent gain: a five-cent tax on disposable shopping bags in Washington DC was found to reduce their use by a substantial amount, while a five-cent bonus for using a reusable bag had essentially no effect on behaviour.