Positive reinforcement of litter removal in the natural environment.

Clark et al. (1973) taped small money or lottery offers to trailhead signs. They wanted to see if hikers would pick up more litter.

The team used an ABAB design. Signs alone came first, then signs plus the reward, then back to signs only, then rewards again.

When the reward was posted, hikers filled more trash bags each week. Ground litter also looked visibly lower.

When the reward disappeared, bag counts dropped. They rose again as soon as the reward returned.

Wolchik et al. (1982) and McGarty et al. (2018) show the same tiny reward still works decades later. A parent lottery lifted child language gains. A 50-cent token lifted caregiver teaching time.

van Schrojenstein Lantman-de Valk et al. (2006), Cooper et al. (1990), and Sievert et al. (1988) got similar behavior jumps with signs alone, no money. This seems like a clash, but the key difference is effort. Picking up trash takes work; grabbing a condom or salad does not. When the act is easy, a clear prompt is enough. When the act costs time, a small reward seals the deal.

Dukhayyil et al. (1973) ran a twin study the same year: a 16-cent daily bonus erased factory tardiness. Together these papers prove micro-cash reliably lifts low-rate community behaviors.

You can nudge almost any low-rate, high-effort community act with pocket change. Post a reward on your sign, token chart, or parent note. Remove it once the habit sticks, then bring it back if numbers fall. The litter study gives you a ready-made ABAB script to sell this idea to parks, schools, or employers.