Motivating vaccination with financial incentives.

Governments and organizations often offer cash payments for vaccination. How effective are such payments? A literature review shows that incentives usually increase vaccination, especially for nonhesitant populations and when using guaranteed payments. Concerns about negative unintended consequences are unsupported. We also discuss open questions and avenues for future research.

Financial incentives for vaccination do not have negative unintended consequences.

Financial incentives to encourage healthy and prosocial behaviours often trigger initial behavioural change1-11, but a large academic literature warns against using them12-16. Critics warn that financial incentives can crowd out prosocial motivations and reduce perceived safety and trust, thereby reducing healthy behaviours when no payments are offered and eroding morals more generally17-24. Here we report findings from a large-scale, pre-registered study in Sweden that causally measures the unintended consequences of offering financial incentives for taking the first dose of a COVID-19 vaccine. We use a unique combination of random exposure to financial incentives, population-wide administrative vaccination records and rich survey data. We find no negative consequences of financial incentives; we can reject even small negative impacts of offering financial incentives on future vaccination uptake, morals, trust and perceived safety. In a complementary study, we find that informing US residents about the existence of state incentive programmes also has no negative consequences. Our findings inform not only the academic debate on financial incentives for behaviour change but also policy-makers who consider using financial incentives to change behaviour.

A citywide experiment testing the impact of geographically targeted, high-pay-off vaccine lotteries.

Lotteries have been shown to motivate behaviour change in many settings, but their value as a policy tool is relatively untested. We implemented a pre-registered, citywide experiment to test the effects of three high-pay-off, geographically targeted lotteries designed to motivate adult Philadelphians to get their COVID-19 vaccine. In each drawing, the residents of a randomly selected 'treatment' zip code received half the lottery prizes, boosting their chances of winning to 50×-100× those of other Philadelphians. The first treated zip code, which drew considerable media attention, may have experienced a small bump in vaccinations compared with the control zip codes: average weekly vaccinations rose by an estimated 61 per 100,000 people per week (+11%). After pooling the results from all three zip codes treated during our six-week experiment, however, we do not detect evidence of any overall benefits. Furthermore, our 95% confidence interval provides a 9% upper bound on the net benefits of treatment in our study.

Association between statewide financial incentive programs and COVID-19 vaccination rates.

To promote COVID-19 vaccination, many states in the US introduced financial incentives ranging from small, guaranteed rewards to lotteries that give vaccinated individuals a chance to win large prizes. There is limited evidence on the effectiveness of these programs and conflicting evidence from survey experiments and studies of individual states' lotteries. To assess the effectiveness of COVID-19 vaccination incentive programs, we combined information on statewide incentive programs in the US with data on daily vaccine doses administered in each state. Leveraging variation across states in the daily availability of incentives, our difference-in-differences analyses showed that statewide programs were not associated with a significant change in vaccination rates. Furthermore, there was no significant difference in vaccination trends between states with and without incentives in any of the 14 days before or after incentives were introduced. Heterogeneity analyses indicated that neither lotteries nor guaranteed rewards were associated with significant change in vaccination rates.

Monetary incentives increase COVID-19 vaccinations.

The stalling of COVID-19 vaccination rates threatens public health. To increase vaccination rates, governments across the world are considering the use of monetary incentives. Here we present evidence about the effect of guaranteed payments on COVID-19 vaccination uptake. We ran a large preregistered randomized controlled trial (with 8286 participants) in Sweden and linked the data to population-wide administrative vaccination records. We found that modest monetary payments of 24 US dollars (200 Swedish kronor) increased vaccination rates by 4.2 percentage points (P = 0.005), from a baseline rate of 71.6%. By contrast, behavioral nudges increased stated intentions to become vaccinated but had only small and not statistically significant impacts on vaccination rates. The results highlight the potential of modest monetary incentives to raise vaccination rates.

Variation in common laboratory test results caused by ambient temperature.

BACKGROUND: Laboratory tests measure important aspects of physiology, but their results also vary for idiosyncratic reasons. We explore an underappreciated source of variation: ambient temperature on the day blood is drawn. METHODS: In a sample of 4,877,039 individuals between 2009-2015, we model 215,234,179 test results as a function of temperature, controlling for individual and city-week fixed effects. This measures how day-to-day temperature fluctuations affect results over and above the individual's mean values, and seasonal variation. FINDINGS: 51 of 75 assays are significantly affected by temperature, including measures of kidney function (increased creatinine, urea nitrogen, and urine specific gravity), cellular blood components (decreased neutrophils, erythrocytes, and platelets), and lipids (increased high-density lipoprotein [HDL] and decreased total cholesterol, triglycerides, and low-density lipoprotein [LDL]). These small, day-to-day fluctuations are unlikely to correlate with long-term physiological trends; for example, lipid panels checked on cooler days look lower risk, but these short-term changes probably do not reflect stable changes in cardiovascular risk. Nonetheless, doctors appear to treat these individuals differently. We observe 9.7% fewer statin prescriptions for individuals checked on the coolest versus the warmest days (-0.42% versus baseline of 4.34%, p < 0.001). CONCLUSIONS: Ambient temperature affects the results of many laboratory tests. These distortions, in turn, affect medical decision-making. Statistical adjustment in reporting is feasible and could limit undesired temperature-driven variability. FUNDING: None.

Exploring Psychology in the Field: Steps and Examples From the Used-Car Market.

The growing availability of large datasets in a variety of domains presents an opportunity for researchers to use field data to better understand psychological concepts. I discuss, from an empirical economics point of view, steps for how to study cognition in large datasets. I use two recent papers that explore psychology in the used-car market as motivating examples. These examples help illustrate the potential importance of big data as a way to explore human psychology and cognition.

Round numbers as goals: evidence from baseball, SAT takers, and the lab.

Where do people's reference points come from? We conjectured that round numbers in performance scales act as reference points and that individuals exert effort to perform just above rather than just below such numbers. In Study 1, we found that professional baseball players modify their behavior as the season is about to end, seeking to finish with a batting average just above rather than below .300. In Study 2, we found that high school students are more likely to retake the SAT after obtaining a score just below rather than above a round number. In Study 3, we conducted an experiment employing hypothetical scenarios and found that participants reported a greater desire to exert more effort when their performance was just short of rather than just above a round number.

Reacting to rankings: evidence from "America's Best Hospitals".

Rankings and report cards have become a popular way of providing information in a variety of domains. I estimate the response to rankings in the hospital market and find that hospitals that improve their rank are able to attract significantly more patients. The average hospital in my sample experiences a 5% change in non-emergency, Medicare patient volume from year to year due to rank changes. These findings have implications regarding the competitiveness of hospital markets and the effect that the dissemination of quality information in hospital markets can have on individual choice.