have been found on time discounting when it comes to obesity (Barlow et al., 2016; Barlow et al., 2016), while altering default settings and providing social reference points have been found to have positive effects on changing physician behavior (Wang & Groene, 2020). Ongoing management of NCDs, mainly via medication adherence, is among the most cost-effective strategies for NCD control (Watkins et al., 2022); the policy tools discussed here can support adherence by addressing barriers that currently prevent individuals from entering and remaining in care, thereby improving the effectiveness of such interventions.

The behavioral science toolkit is large. No single policy tool can address the complexity of behavioral barriers across the whole journey towards healthy aging. Nor should these be considered stand-alone interventions that can operate independently of other services, health system resources, and other structural factors. It is in the combination of a strong structure of opportunities to adjust behaviors and habits, supported by motivation and a sense of ability to act, that behavior change can take place and be sustained over time. The policy toolkit outlined here is both ample and complimentary to existing policy efforts. These efforts include classical interventions such as taxation, subsidies, or restrictions. The purpose of this review is not to compare the effects of behavioral and classical interventions; however, we emphasize the need for future studies to evaluate how different combinations of behavioral and classical tools can maximize the effect to achieve healthy aging.

In terms of interpretation, the tools described below can be linked to the original framework by way of identifying the _‘Behavioral Phenotype’_ of a given policy’s intended target population. This means identifying and segmenting the target population not only by risk characteristics or sociodemographic traits but based on a larger set of profile elements, including behavioral and psychological variables, motivation, ability, and opportunity factors. While for some people reminders are all that is needed to close gaps in treatment adherence, for others more complex interventions to inform, motivate, and create adequate social support might be required.

The tools and literature presented in this section are a selection of the relevant evidence that speaks to the three stages of NCD formation, detection, and management. We leveraged randomized field interventions and systematic reviews to showcase the behavioral toolkit available to policymakers to tackle NCDs. However, the selection is not the result of a systematic review. The literature search strategy comprised English-language, peer-reviewed electronic records from Google Scholar published between 2000 and 2022. Reference lists of relevant studies were also hand searched for eligible papers. The approach prioritized studies from low- or middle-income countries and was supplemented with evidence from highincome countries. The selected field studies, mega-studies, and systematic reviews conducted or assessed randomized controlled trials (RCT) to measure the interventions’ effectiveness.

We gave precedence to mega-studies and systematic reviews to ensure the external validity or generalizability of the tools. However, there are gaps where evidence is mixed or very limited, and this is reflected in the toolkit. There is a more robust evidence-base related to financial incentives on a wide range of behaviors, as compared with salience or plan-making. We also have little information about the persistence of the reported effects for even the most successful interventions, as studies of this kind rarely follow participants for more than a few months after the intervention. This limitation is most important for interventions that aim to build habits, for example around exercise, as opposed to interventions focused on one-time (or infrequent) behaviors such as screenings.

20