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Attractive Flu Shot: A Behavioral Approach to Increasing Influenza Vaccination Uptake Rates
Last registered on October 16, 2019

Pre-Trial

Trial Information
General Information
Title
Attractive Flu Shot: A Behavioral Approach to Increasing Influenza Vaccination Uptake Rates
RCT ID
AEARCTR-0004584
Initial registration date
August 22, 2019
Last updated
October 16, 2019 9:01 AM EDT
Location(s)
Primary Investigator
Affiliation
University of Haifa
Other Primary Investigator(s)
PI Affiliation
Tel Aviv University and Sarid Research Institute
Additional Trial Information
Status
Completed
Start date
2019-08-25
End date
2019-09-30
Secondary IDs
Abstract
We suggest and examine a behavioral approach to increase seasonal influenza vaccine uptake based on the behavioral phenomenon known as the attraction effect. Using the seasonal nature of the flu, we present participants in a hypothetical survey with two options to receive the shot: early in the season, which is recommended and hence ``attractive'', or later. Three additional layers along which the early shot outperforms the late one are to be examined. We will compare intentions to get vaccinated when facing these options to those of a control who will be invited to get the shot regardless of timing.
External Link(s)
Registration Citation
Citation
Maltz, Amnon and Adi Sarid. 2019. "Attractive Flu Shot: A Behavioral Approach to Increasing Influenza Vaccination Uptake Rates." AEA RCT Registry. October 16. https://doi.org/10.1257/rct.4584-2.0.
Experimental Details
Interventions
Intervention(s)
We will run an online hypothetical survey that will include an invitation to receive the flu shot that participants will be asked to imagine they will receive on October 1st by their HMO. The survey will be sent out to a sample of the adult Israeli population (N=3,250). Participants will be randomly assigned into either the control or one of the treatment groups. In our treatment groups (the intervention groups) participants will be introduced with two options to receive the shot: early in the season, which is recommended by the ministry of health and hence ``attractive,'' or later. Three additional layers along which the early shot outperforms the late one will be examined across treatments. In the control, participants will simply be invited to receive the shot regardless of timing.

We will compare vaccination intentions (using the self report of the participants in the survey) in these treatments to those of the control group.
Intervention Start Date
2019-08-25
Intervention End Date
2019-09-30
Primary Outcomes
Primary Outcomes (end points)
Our main dependent variable is the self reported intentions of getting the vaccine or not (in the treatment groups the report will be getting the shot early, late or not at all). Our independent variables will be the treatment to which the participant belongs (we will have random assignment to the different treatments) and a measure of the level of certainty of the participant with respect to his/her intentions of getting the vaccine. As controls we will look at vaccination last year, number of vaccinations in the past 5 years and we will also have demographic information such as age, gender, self reported income and education which is kept in the survey company's data set.
Primary Outcomes (explanation)
The main variables of interest are straightforward. Subjects will report whether or not they plan to get the shot (in the treatment groups the report will be getting the shot early, late or not at all). The measure of level of certainty will be determined by the question asking how certain the participant feels regarding getting the flu shot which will be answered on a 5-point Likert scale.
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
The design is mostly described in the intervention section above. The experiment is based on a survey which will be distributed to a sample (N=3,250) of the Israeli adult population through a panel company which has a large number of registered panelists. In the survey participants will be asked to imagine that on October 1st they will receive a message from their HMO inviting them to receive the seasonal influenza vaccine. Invitations in all groups will inform the reader about the flu and the vaccine, mention that receiving the shot is recommended by the ministry of health and state that it is available through the end of March the following year, the date until which flu shots are normally offered in Israel.

In the control, the invitation message will be along the lines of the one used in Israel these days in which only the basic information about the flu and the vaccine is provided. Following this information, we will ask participants in the control group whether they plan on taking the shot (which is free of charge) or not. In the four treatments (intervention groups), following the basic information, two options to receive the vaccination will be introduced: an early option, which is recommended by the ministry of health, and a late option. Three of the four treatments will add another dimension along which the early shot is better than the late one.

Following the invitation in all treatment groups, we will ask our participants to mark whether they plan on getting the vaccine early, late or not at all (this is our main dependent variable). In the control they will simply be asked whether they plan on getting the shot or not.

Following these questions we will ask participants for a free text explanation of their answer and their level of certainty with respect to their intention to get the shot. Finally we will ask them whether or not they received the shot last year and to give their best answer to the question of how many times they received the flu shot in the last 5 winter seasons (a multiple choice question).
Experimental Design Details
The design is mostly described in the intervention section above. The experiment is based on a survey which will be distributed to a representative sample (N=3,250) of the Israeli adult population through a panel company which has a large number of registered panelists. In the survey, participants will be asked to imagine that on October 1st they will receive a message from their HMO inviting them to receive the seasonal influenza vaccine. Invitations in all groups will inform the reader about the flu and the vaccine, mention that receiving the shot is recommended by the ministry of health and state that it is available through the end of March the following year, the date until which flu shots are normally offered in Israel. In the control, the invitation message will be along the lines of the one used in Israel these days in which only the basic information about the flu and the vaccine is provided. Following this information, we will ask participants in the control group whether they plan on taking the shot (which is free of charge) or not. In the four treatments (intervention groups), following the basic information, two options to receive the vaccination will be introduced: an early option, which is recommended by the ministry of health, and a late option. Three of the four treatments will add another dimension along which the early shot is better than the late one (therefore we will have 5 treatments overall: the control and four intervention treatments). Here are the main dimensions along which the early shot is better than the late one according to the different treatments: 1. The early shot is recommended by the ministry of health. 2. Mentioning that the vaccine is more likely to run out of stock later in the season compared to early in the season. 3. The early shot is free while the late one costs a fee of 20 ILS (roughly 5.5 USD). 4. The early shot carries a monetary benefit of 20 ILS which may be used for doctor visits within the HMO. Following the invitation in all treatment groups, we will ask our participants to mark whether they plan on getting the vaccine early, late or not at all (this is our main dependent variable). Following the first question in each treatment (getting the shot early/late or not) we will ask participants 4 more questions: 2. Freely explain why they chose what they did in the first question. 3. How certain they are (on a scale of 1 - 5) regarding their willingness to get the shot. 4. Whether or not they received the vaccine last year. 5. How many times they received the flu shot in the last 5 winter seasons (a multiple choice question which may be answered according to their memory if they are not sure). A detailed explanation of our hypotheses, planned analysis and rule for number of participants (which is based on a pilot study and the pwr package in R) are given in the data analysis document attached to this pre-registration. All surveys are also attached to this pre-registration (in one document).
Randomization Method
Randomization by computer.
Randomization Unit
Individual randomization into treatments.
Was the treatment clustered?
No
Experiment Characteristics
Sample size: planned number of clusters
3,250
Sample size: planned number of observations
3,250
Sample size (or number of clusters) by treatment arms
650 subjects per treatment. 650 in the control and 650 in each intervention treatment.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
The power calculation has been based on a pilot study which was run using 1,151 participants during 2016 and 2017. The calculation was run using the pwr package in R and took into consideration the average effect size found in the pilot study and alpha=0.5. For more information see the planned analysis document.
Supporting Documents and Materials

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IRB
INSTITUTIONAL REVIEW BOARDS (IRBs)
IRB Name
University of Haifa
IRB Approval Date
2016-07-31
IRB Approval Number
260/16
Analysis Plan

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Post-Trial
Post Trial Information
Study Withdrawal
Intervention
Is the intervention completed?
Yes
Intervention Completion Date
September 10, 2019, 12:00 AM +00:00
Is data collection complete?
Yes
Data Collection Completion Date
September 10, 2019, 12:00 AM +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
3,271 participants: 659 in the control, 644 in the recommendation treatment, 644 in the stock treatment, 663 in the cost treatment and 661 in the benefit treatment.
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
3,271 participants: 659 in the control, 644 in the recommendation treatment, 644 in the stock treatment, 663 in the cost treatment and 661 in the benefit treatment.
Final Sample Size (or Number of Clusters) by Treatment Arms
See above.
Data Publication
Data Publication
Is public data available?
Yes
Program Files
Program Files
Yes
Reports and Papers
Preliminary Reports
Relevant Papers