Schultz, 1999: Promoting recycling with individual or group feedback increased recycling among low-recycling homeowners in La Verne, California
605 homes in La Verne, California were randomized to a control condition or one of four treatments, delivered, via weekly green door hangers, over 5 weeks to promote recycling: (1) information that their home would be included in a study of recycling and a plea to recycle (“please try to recycle as much as possible”) (plea condition); (2) the same content as (1) plus information about recycling, including what materials are recyclable, contaminants (information condition); (3) the same content as (1) plus individual feedback about how much material had been collected at their home the previous week and in the current week and the total amount collected for the duration of the study (individual feedback condition); or (4) the same content as (1) and (3) plus information about their residential area, including the amount of material collected in this area the previous week and in the current week, the total amount collected for the duration of the study, and the percentage of households participating that week, provided in the form of average participant behavior (average amount of material per week and average participation rate per week) (group feedback condition). As compared to a baseline observation period 2 months earlier, observations over the 4 intervention weeks and the subsequent 4 weeks (no contact) showed that participants in the individual and group feedback conditions were most likely to recycle and recycled the most materials. There was no effect of condition on the level of contamination. The benefits of the feedback conditions were concentrated in households that, at baseline, were less likely to recycle (bottom 33%), increasing from 6% participation rate (control) to 24% (individual feedback) and 13% (group feedback).