To investigate the effect that hunters and jostlers may have on vaccinations, we conducted two pre-registered and monetary incentive study experiments – a “main study” and a “follow-up study”.
Data for the main study were collected on the Prolific platform at a time (March 22-24, 2021) when COVID-19 vaccines were still unavailable to large groups of the adult American population. We recruited a sample of Americans, representative of the population by age, gender, and race / ethnicity. The study experiment was pre-registered in the AEA registry for RCTs as AEARCTR-0007285. Informed consent was obtained from all participants, the experiment was performed in accordance with relevant guidelines and rules, and the experimental protocol was approved by George Mason IRB (# 1724890).
Participants were paid $ 1 to complete, plus any incentives earned as part of the study. While a total of 1,503 participants responded to the study, we focus here on those (N = 1,117) who were randomized to the following treatments: i) a control treatment (participants received information about the existence of COVID-19 vaccines); ii) a “hunters” treatment (participants were also given brief information describing how vaccine hunters went to great lengths to secure remaining vaccine doses); and iii) a “jostler” treatment (which provides similar information about how some privileged people skipped the vaccine line). The remaining 386 of the participants in the total sample (N = 1,503) were randomized to a “safe” treatment. The safe treatment emphasized the safety of COVID-19 vaccines and was included to provide a benchmark for the magnitude of any treatment effects in the treatment of hunters and jostles. However, the safe treatment did not affect the enthusiasm for the vaccines (probably because our sample already has a very high level of confidence in the safety of the vaccines – more than 85% of the participants thought that the vaccines were safe). Information about the safe treatment, its (zero) results and about our participants’ trust in the vaccines can be found in More info.
Specifically, the participants in the control group were shown information about the existence of COVID-19 vaccines, i.a.[t]The COVID-19 vaccines will reduce your risk of getting COVID-19 and of becoming seriously ill or dying […]. As COVID-19 vaccines prevent coronavirus from spreading and replicating, they will also help prevent further mutations of the virus. “
In addition to the information provided in the control group, participants in the hunter and jostler treatment saw information describing the respective phenomenon. We made sure that the information contained language similar to that used in news media, e.g. how the lack of vaccine in the early spring of 2021 fueled the behavior of hunters and jostlers. Participants randomized to the hunters’ treatment read: “Even though the vaccines have been approved, the supply is still too low to meet the demand. This has led to the global rise of so-called ‘vaccine hunters’ […]. The vaccine hunters wait for whole days outside, for example, grocery pharmacies in the hope of securing leftover vaccine doses (which would otherwise be discarded) at the end of the day. “Those who were randomized to jostler’s treatment read:” too low to meet demand. This has led to a situation where the wealthy globally are trying to skip the queue to get a COVID-19 vaccine […]. An example of this is the Canadian billionaire Rod Baker, who together with his wife chartered a private plane and traveled to a remote region of the Yukon to pose as a motel worker to pretend to be eligible for the vaccine. ” Immediately after the treatment information, participants answered a short question about the main message of the section. This was done to identify participants who may not have paid enough attention or misunderstood the text. However, such limited attention / misunderstandings were uncommon: only 2.95% of participants gave a wrong answer, and our results are robust to rule them out.
Four outcome measures were assessed immediately after treatment. First, we asked participants to indicate their (1) willingness to be vaccinated immediately [VAXTODAY]and (2) in two months [VAX2MONTHS] on a 1-10 scale (from absolutely not willing to absolutely willing). If participants had already received at least their first vaccine dose, these measures assessed their willingness to recommend vaccination to friends and family using the same scale. Participants were then asked if they (3) wanted (yes / no) to receive a link to general vaccine eligibility and enrollment information (for self-use or to friends and family) in the confirmation email after the study. [VAXINFO].
The last outcome variable, which was only asked of participants who had not yet received at least a first COVID-19 vaccine dose, measured their (4) monetary valuation of a vaccine enrollment service that facilitated access to a COVID-19 vaccine. Specifically, the service provided individualized assistance in identifying and signing up for a COVID-19 vaccine agreement in the participant’s geographical vicinity when the participant was eligible (at the time of data collection in March 2021, most adults in the United States were still not eligible and many people were eager to to get their vaccines as soon as they became eligible). Further information on the vaccine registration service and how it was made available to participants is available in More info.
Willingness to pay for the vaccine registration service was elicited using a multiple price list, MPL28Participants were presented with a list of eight election pairs. In each election pair, participants had to choose between either accessing the vaccine enrollment service or receiving a cash prize ($ 2, $ 5, $ 10, $ 25, $ 50, $ 75, $ 100 and $ 200 in the eight election pairs, respectively). Participants were informed that 15 participants in the study would be randomly selected and that their preferred alternative in a randomly selected pair out of the eight would be implemented (i.e., they would either receive the cash prize or access to the vaccine enrollment service, depending on their chosen alternative in a randomly selected pair of choices). Pair pairs were ordered from the lowest to the highest amount of money so that we can use the number of times a participant chose the vaccine enrollment service before switching to the cash prize as a measure of their willingness to pay for the service. [VAXHELP]. The final part of the study assessed participants’ demographic information.
Of the 15 people randomly selected to receive their preferred alternative in MPL, 3 participants preferred the vaccine enrollment service in the randomly selected pair, and 12 participants received a cash prize (which averaged $ 62).
While the sample, by design, is quota representative of the American population on gender, age, and race / ethnicity, it is not necessarily representative in other respects. It is noteworthy that close to 60 percent (59.4 percent, SE = 1.3) of our sample have completed at least one four-year college education, which is a higher proportion than in the general U.S. population. As education correlates positively with beliefs that vaccines are generally safe1,2,3,4,5,6,7,8,9this may (at least in part) explain the large proportion of our participants who believe that COVID-19 vaccines are safe.
The willingness to be vaccinated is generally high in our sample. In the control treatment, 82.6, SE = 1.9, (84.6, SE = 1.8) percent were more willing than unwilling to receive / recommend the vaccine immediately (in two months). In any case, this is slightly higher than similar proportions observed in most studies assessing the willingness to be vaccinated against COVID-19 in the United States.1,2,3. Of the participants in the control treatment, 42 percent (SE = 2.49) stated that they wanted to receive information about eligibility and registration for COVID-19 vaccines. However, the willingness to pay for the vaccine enrollment service is low: the average participant in the control group only chooses the vaccine service over the cash prize in 0.85 (SE = 0.11) of the 8 questions, indicating an average WTP of less than $ 2.
We examined the balance between demographic and attitude variables across treatment groups by performing 36 pairwise t-tests (two-sided) of equal means. One test was statistically significant (s<0.05): we find that the proportion of female participants is higher in the hunters than in the control treatment group. Although this is not surprising with 36 pairwise tests, we therefore include the variable 'she' as a control variable in our main regression specifications reported in fig. 1 and table 1 (exclusion of this control variable, however, does not affect the reported results or conclusions).
To better understand the effect on the willingness to vaccinate from the treatments of the hunters and jostles that we observed in the main study, we then conducted a “follow-up study.” The data collection took place on May 19, 2021 at Prolific, and the participants were 800 Americans, separated from those who responded to the first survey. They were paid $ 1 for completion, plus any incentives earned as part of the study. The experimental study used in the follow-up study elicited participants’ emotional response to the control and treatment information in the “main study”, as well as their incentive predictions about the effect of treatment information on willingness to be vaccinated. This study was pre-registered in the AEA Register of RCTS as AEARCTR-0007656. Informed consent was obtained from all participants, the experiment was performed in accordance with relevant guidelines and rules, and the experimental protocol was approved by George Mason IRB (# 1756922-1).