How a lottery system helped 10 patients stay on their medication 24% more often

Intervention · Health


Millions of patients are at risk of stroke and bleeding complications due to poor adherence to warfarin, a blood clot medication. They may take the wrong dosage, fail to take it all, or accidentally take a different medication.

Volpp et al. ran two pilot studies to investigate how financial incentives affect adherence. The researchers looked at whether a lottery system—in which patients were enrolled in a lottery if they adhered to their prescribed warfarin regime—could i) lead patients to take the right dosage of warfarin, and ii) lead patients to take warfarin, as opposed to another medication. 


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Rating = 4/5 (small sample size; potentially unsustainable long-term, direct positive impact)

How A Lottery System Helped 10 Patients Correctly Take Their Warfarin
Lottery System 1 
2 in 5 chance to win $10
1 in 100 chance to win $100
23.8% decrease in time spent medically unstable
19.7% decrease in incorrect pill consumption
Lottery System 2 
1 in 10 chance to win $10
1 in 100 chance to win $100
24.6% decrease in time spent medically unstable
24.4% decrease in incorrect pill consumption

Key Concepts

Incentives: An incentive is any measure that changes the content of a choice in order to motivate people to choose in a certain way. (This contrasts them with nudges, which change the choice architecture—but not the choices themselves—to get people to choose in a certain way.)  

Incentivization: Incentives work, when properly implemented, because humans have a bias towards incentivization—what we choose depends on what rewards or punishments we receive.

The Problem

Millions of patients have conditions that increase their risk for strokes, bleeding complications, and heart-related problems. These conditions often come with an increased risk for morbidity (long-term suffering from a health condition) and mortality. For most of these patients, preventative blood clot medicine like warfarin can decrease these health complications.

Nonetheless, poor adherence to blood clot prevention pills is fairly common. In one study, researchers found that 40% of patients missed at least 20% of their warfarin doses; and in general, 32-68% of patient time is spent outside of the heathy coagulation range, in large part due to a lack of adherence to their prescribed warfarin regime. This inadequate regulation not only makes patients more susceptible to health complications—it reduces warfarin’s benefit, comes with side effects, and makes physicians more reluctant to prescribe warfarin to these patients in the first place. There is a great need for an intervention that helps patients adhere to their prescribed warfarin regime.


Who did they study?

Volpp et al. ran two pilot tests to see whether a financial incentive could help keep patients on their warfarin regime. The researchers chose lotteries due to their popularity in the United States–over 50% of U.S. adults participate in the lottery at least once per year. Ten patients who had been taking warfarin for at least three months were enrolled in both pilot tests. To participate, all ten signed a written consent form. 

How did they study them?

The researchers made sure they had a home telephone line, and that they could keep track of the pill monitor. Each participant was given an Informedix Med-eMonitorTM System, which tracked and displayed a patient’s medication compartments. The system used a participant’s home telephone line to directly collect data in a centralized database that the study’s administrator could access. 

What did they offer?

In the first pilot study, the expected value of the lottery was $5, with a ⅖ chance of winning $10, and a 1 in 100   chance of winning $100 dollars.  In the second pilot study, the expected value was $3, with a 1/5 chance of winning $10, and a 1/100 chance to win $100. For both studies, patients were enrolled in the lottery only if the Med-eMonitor showed that they had adhered to their warfarin regime, either by taking their prescribed dosage of warfarin or by not taking it when they were not supposed to. 

What did they look for?

The study measured two metrics. First, it measured how long a patient was outside their recommended coagulation levels. (It is unclear if the Med-eMonitor measured or estimated this information.) Second, it measured patient adherence, based on the mean days that the patient opened the correct cabinet and recorded pill taking. To make sure the intervention was effective, each study’s results were then compared with historical group controls or to the patient’s own medical history, which was measured by the Medication Event Monitoring System (MEMS) before the study began.

One way to understand this study’s design is through the “COM-B” framework:

  • Capability: patients were both physically and psychologically able to access their medication.
  • Opportunity: there were no external physical barriers stopping patients from accessing their medication. The study does not discuss whether there are also any social barriers towards regiment adherence. 
  • Motivation: the intervention sought to increase patients’ motivation to follow their prescribed regimen through a financial incentive.
  • Behavior: Given the lack of physical and psychological barriers, an increase in motivation was hoped to lead to an increase in warfarin adherence among patients.

Results and Application

First pilot

In the first pilot study, participants’ time in an out-of-range coagulation level was decreased by 27.8% compared to before the intervention. (Notably, in the time period after the intervention, the participants returned to pre-intervention rates.) Additionally, participants also experienced a 19.7% reduction in incorrect pill consumption.

Second pilot

The second pilot study, with a reduced expected value, enjoyed similar results: there was a 24.6% decrease in participants’ time with an out-of-range coagulation level, and incorrect pill consumption reduced by 20.4%.


One caveat to note, however, is that the studies’ sample size was small (N = 10) and non-randomized. Therefore, it is unclear whether these promising results would scale in the real-world. The researchers acknowledge that more research is needed before drawing further conclusions.

Health & Wellbeing Some studies (also conducted by Volpp et al) argue that a lottery system could lead to significant weight loss compared to a control group.
Public Policy In Ohio, a lottery system was used to incentivize Ohioans into receiving their COVID-19 vaccine.2
Education Some studies suggest that performance-based financial incentives (scholarships) can lead students to devote  more time and effort to educational activities.3


  • Researchers made sure the intervention was safe and effective for participants.
  • Participant consent was explicitly gathered, though it is unclear whether the monitor tracked additional data.
  • Small, non-randomized sample limits the results’ validity, as well as the diversity of the participant set.

Does the intervention demonstrably improve the lives of those affected by it?
There was a significant decrease in unprescribed coagulation levels, along with a significant increase in warfarin regimen adherence.
Does the intervention respect the privacy (including the privacy of identity) of those it affects?
Insufficient Information
While we know that the Med-eMonitor collected data on patient pill consumption, it is unclear whether the monitor also collects other data.
Does the intervention have a plan to monitor the safety, effectiveness, and validity of the intervention?
Room for Improvement
Metrics for effectiveness were intentionally designed. Additionally, researchers sought out participants who could feasibly and safely carry out the requisite tasks. However, the researchers admit the sample size is too small to make any grand conclusions.

Does the intervention abide by a reasonable degree of consent?
Every participant had to sign a written consent form before participating.
Does the intervention respect the ability of those it affects to make their own decisions?
Room for Improvement
The researchers acknowledge that the intervention could make patients feel their ability is being disrespected. (Since they are being paid to do what they are supposed to.) However, in the limited sample size of the study, there were no reports of this.
Does the intervention increase the number of choices available to those it affects?
Not Applicable
The number of choices stayed the same.

Does the intervention acknowledge the perspectives, interests, and preferences of everyone it affects, including traditionally marginalized groups?
Room for Improvement
While the researchers consider the health risks for the patients, it does not consider social barriers preventing some patients from following their prescribed regiment.
Are the participants diverse?
Room for Improvement
Given the small, non-randomized sample size, it is unlikely that the participant set was diverse.
Does the intervention help ensure a just, equitable distribution of welfare?
Given that minorities tend to disproportionately bear negative  health outcomes (including heart-related problems), this intervention indirectly helps in that regard.

Related TDL Content

Gold Stars for Staying Home: Rewards and COVID-19

In this intervention, Volpp et al focused on the power that positive incentives—namely, a potential financial reward—could lead patients towards safer behavior. Yet, when it has come to promoting safe behavior during the COVID-19 pandemic, policy makers have largely focused on negative incentives—for instance, the fear of getting ill. In this article, Hannah Chappell argues that positive incentives could also help promote safe behavior among citizens during this ongoing pandemic.     

Should We Pay Students to Go to School?

Earlier, we saw that some studies suggest using financial incentives to increase a student’s time and effort devoted to school. However, some have proposed directly paying students to incentivize them to go to school, in the hopes that this incentive will decrease the number of people who drop out of school. In this article, Tony Jiang outlines where this sort of intervention has been applied (e.g., the Nordic Countries, Mexico, etc.), and its effectiveness in the short-term.


  1. Volpp, K. G., Loewenstein, G., Troxel, A. B., Doshi, J., Price, M., Laskin, M., & Kimmel, S. E. (2008). A test of financial incentives to improve warfarin adherence. BMC Health Services Research8(1), 272.
  2. Walkey, A. J., Law, A., & Bosch, N. A. (2021). Lottery-Based Incentive in Ohio and COVID-19 Vaccination Rates. JAMA326(8), 766.
  3. Barrow, L., & Rouse, C. E. (2018). Financial Incentives and Educational Investment: The Impact of Performance-based Scholarships on Student Time Use. Education Finance and Policy13(4), 419–448.
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