Humans are social beings; they seek information about what relevant others do and adjust their behavior to fit in to the group [
1,
2]. When people believe that a crowd behaves in a certain way, they are likely to conform to what the crowd does [
3]. These rules that govern behavioral expectations within groups are called social norms [
4]. A behavioral pattern that is conditional only on a person’s belief about what is commonly done is known as a descriptive norm [
5].
Program implementers and researchers have utilized descriptive norms messaging as an intervention technique to increase individual and social benefit for a broad range of public health and sustainability programming—from increasing vegetable consumption [
6] and discouraging alcohol misuse amongst college students [
7] to reducing plastic bag use [
8]. However, evidence suggests that people who have adopted desirable behaviors sometimes regress to undesirable behaviors after receiving descriptive norms messages due to the type of information provided in the messaging [
9,
10]. This phenomenon is called the boomerang effect [
10]. The boomerang effect refers to when people who exhibit a desirable behavior become less likely to do so after being exposed to descriptive information about others that indicates the desirable behavior is less frequent, occurs to a lesser degree, or is not exhibited amongst other people in relevant social groups [
10]. Studies examining boomerang effects after exposure to descriptive norms messaging interventions have yielded inconsistent results. One study, for example, found that households with relatively low energy use increased their energy consumption after receiving descriptive information about their neighbors’ average energy use, as the average was higher than their own relatively low consumption levels [
10]. Conversely, a study of an intervention designed to correct college students’ exaggerated perceptions of alcohol use on college campuses found that lighter drinkers who drink less than the typical student did not increase drinking after receiving personalized descriptive norms messaging [
11]. This inconclusive evidence regarding the intervention effects of descriptive norms interventions warrants further examination into potential, yet unintended boomerang effects that result from exposure to descriptive information regarding relevant others’ behaviors.
Previous systematic reviews have examined the effectiveness of descriptive norms messaging interventions on targeted behaviors amongst entire intervention populations [
12‐
14] and the unintended boomerang effects of information-based interventions [
15,
16]. However, to our knowledge, no known reviews have examined boomerang and differential effects of descriptive norms messaging interventions amongst subgroups of intervention populations based on their behavior prior to intervention exposure. To fill in this gap, our systematic review will synthesize evidence regarding potential boomerang effects of descriptive norms messaging interventions designed to change behaviors related to health and environmental sustainability. More specifically, the aim of this review is threefold. First, we aim to examine peer-reviewed literature evaluating descriptive norms messaging interventions that promote health and environmental sustainability behaviors. Second, we aim to synthesize evidence regarding intervention effects on subgroups that behave differently prior to intervention exposure, and determine the magnitude and direction of such effects on people who practice desirable behaviors prior to being exposed to descriptive information that indicates others practice the desirable behavior to a lesser extent or not at all (i.e., boomerang effect). Third, we aim to identify factors that account for heterogeneity of boomerang effects.