Beyond the Facts: Information, Persuasion, and Belief Change

This project investigates how the identity of a communicator and the format of their message influence individuals’ beliefs and intentions regarding vaccination, while ensuring that the informational content itself is identical across conditions.

The study evaluates how the medium of communication and the identity of the speaker affect how individuals receive and respond to a public health message about vaccination.

Participants are exposed to a standardized informational message describing the benefits and safety of vaccines and the role of immunization in preventing infectious diseases. The informational content of the message is identical across all treatment conditions. The message is delivered through videos featuring well-known Greek public figures whose professional identity varies across conditions.

Two types of speakers are featured:

Medical experts (scientists): practicing physicians and medical researchers affiliated with Greek medical institutions.

Social media influencers: Greek public communicators with a large online presence who regularly engage with young audiences.

In total, the study includes four speakers, varying by both professional identity and gender:

male scientist

female scientist

male influencer

female influencer

All speakers deliver the same scripted informational message.

The experiment varies two dimensions of the communication environment.

1. Medium of delivery

Participants are randomly assigned to one of three conditions:

Control: participants watch a short neutral video unrelated to vaccination.

Video: participants watch the informational message delivered by the speakers in a standard two-dimensional video on a computer screen.

Virtual Reality (VR): participants experience the message through a head-mounted VR device in an immersive virtual environment while watching the same video content.

2. Speaker identity

Among participants assigned to the information treatment (Video or VR), the message is delivered by speakers whose identity varies along two dimensions: professional identity (scientist vs influencer) and gender (male vs female). Participants view a sequence of short informational segments delivered by the four speakers.

The order of appearance of the speakers and the pairing between speakers and informational segments are randomized across participants to ensure that message content is not mechanically confounded with speaker identity.

The experimental session consists of three main stages.

Pre-treatment survey

Participants complete a baseline questionnaire collecting demographic characteristics, prior beliefs about vaccines, trust in the healthcare system, attitudes toward science and public institutions, and information on their social networks.

Informational exposure

Participants are exposed to the informational content according to their assigned experimental condition (Control, Video, or VR).

Post-treatment survey

Immediately after the informational exposure, participants complete a follow-up questionnaire measuring outcomes such as trust in vaccines, trust in the healthcare system, evaluation of the speaker and the message, and willingness to discuss vaccination-related topics with others.

Measures of trust in vaccines and trust in the healthcare system are collected at three points in time: pre-treatment, immediately after the intervention, and in a follow-up survey.

For participants assigned to the VR condition, the system also records behavioral engagement measures using the eye-tracking capabilities of the VR headset, including indicators of visual attention to the speaker during the experience.

The experiment takes place in a laboratory setting. Participants receive a fixed participation payment and are entered into a lottery for Apple products. The study procedures are identical across conditions except for the experimentally manipulated communication medium and the identity of the speaker.

2025-12-01

2026-02-13

The primary outcomes capture participants’ beliefs and attitudes toward vaccination and public health institutions following exposure to the informational intervention. The main endpoints are summary indices constructed from post-treatment survey responses:

Trust in Vaccines Index

Trust in Healthcare System / Health Authorities Index

Vaccination Acceptance / Vaccination Intent

These outcomes measure the extent to which exposure to the informational message affects participants’ trust in vaccination, trust in medical institutions, and willingness to accept vaccination recommendations.

Each index will also be analyzed through its individual components as secondary specifications.

Trust in Vaccines Index

This index captures participants' beliefs about the effectiveness, safety, and importance of vaccines. It is constructed using responses to the following four items measured on a 0–10 scale:

"Vaccines are effective at preventing pandemics and serious diseases."

"Vaccines are safe for human health."

"Vaccines are important for your own health."

"Vaccines are important for public health."

Trust in Healthcare System Index

This index measures trust in institutions responsible for health and medical care. It is constructed using 0–10 trust questions on:

"conventional medicine and surgery,"

"doctors and healthcare professionals,"

"public health authorities."

The main specification constructs a standardized index using principal component analysis (PCA) applied to these items. The first principal component will be used as the index. The PCA weights will be estimated using the full sample of post-treatment responses. We will also present results by the individual variables.


Vaccination Intent and Vaccination Status (Follow-up Survey)

The follow-up survey includes two measures related to vaccination behavior:

Willingness to vaccinate, capturing participants' stated intention to receive a vaccine.

Vaccination status, indicating whether the participant reports having received the vaccine.

Both variables are coded as as a binary indicator equal to one if the participant reports being more willing to vaccinate or having been vaccinated.

These outcomes allow us to examine whether exposure to the intervention affects both stated vaccination intentions and realized vaccination behavior at follow-up.

Secondary outcomes measure mechanisms through which the intervention may affect attitudes toward vaccination, as well as additional behavioral and evaluative responses to the informational message.

The main secondary outcomes include:

Willingness to discuss vaccination

Perceived credibility and evaluation of the speaker

Engagement and visual attention during the message (VR condition)

These outcomes help identify the channels through which communication medium and speaker identity influence beliefs and attitudes toward vaccination.

Willingness to Discuss with Others (Family and Friends)

This outcome captures whether the intervention changes participants' willingness to discuss different issues with others. It is measured immediately after the intervention using 0–10 scales, where higher values indicate greater willingness to discuss the topic with others (family and friends). The post-treatment survey includes the following items:

willingness to discuss vaccines;

willingness to discuss the healthcare system;

willingness to discuss social media;

willingness to discuss artificial intelligence;

willingness to discuss politics.

The main secondary outcome in this family is willingness to discuss vaccines. The other items serve as comparison or placebo discussion topics and allow us to assess whether treatment effects are specific to vaccination or extend to other domains.


Evaluation of the Speaker and of the Message

These outcomes capture participants' overall impressions of both the messenger and the informational content. They are measured immediately after exposure using a scale from -5 to 5, where higher values indicate a more positive impression. The post-treatment survey includes the following two items:

overall impression of the speaker;

overall impression of the message.

These variables are analyzed separately and capture whether the intervention changes participants' general evaluation of the person delivering the information and of the public health message itself.

Speaker Evaluation and Credibility

These outcomes capture how participants perceive the messenger delivering the public health message. They are measured immediately after exposure using 0–10 scales, where higher values indicate a more favorable evaluation of the speaker. Participants evaluate the speaker along the following dimensions:

charismatic;

persuasive;

reliable;

knowledgeable;

nice;

attractive;

passionate.

In addition to analyzing each item separately, we will construct a Perceived Speaker Quality Index using principal component analysis (PCA). The index will correspond to the first principal component of these seven items.


Visual Attention and Engagement (VR Condition)

For participants assigned to the VR condition, the study records behavioral engagement measures using the eye-tracking capabilities of the VR headset. These measures capture visual attention and engagement during exposure to the message. In particular, we will use indicators such as:

the share of time the participant's gaze is directed toward the speaker during the VR experience;

related gaze-based engagement indicators recorded by the device.

These measures are available only for participants in the VR condition and are used to study mechanisms related to attention and immersion during the informational exposure

The study randomly assigns participants to receive identical informational content delivered by either a scientific expert or a popular non-expert communicator. This design allows us to compare the influence of messenger identity on beliefs, attitudes, and intentions.

The study is a laboratory experiment designed to evaluate how the medium of communication and the identity of the messenger influence the reception of a public health message about vaccination.

Participants are recruited from the student population of a large university and participate in laboratory sessions conducted at the laboratory of the Athens University of Economics and Business. Each participant completes the study individually at a laboratory workstation. Participants assigned to the virtual reality condition use a head-mounted VR device, while participants assigned to the video condition or the control condition view the content on a standard computer monitor.

The study follows a mixed experimental design combining between-participant and within-participant variation.

The between-participant dimension randomizes the communication medium:

Virtual Reality (VR): participants experience the message in an immersive virtual environment using a VR headset.

Video: participants watch the same message presented as a standard two-dimensional video on a computer screen embedded in the survey interface.

Control: participants watch a neutral video embedded in the survey.

Participants assigned to the information treatment (i.e., those in the Video or VR groups) are randomly assigned to receive the same health message from either:

a medical expert (scientist) – a physician or medical researcher;

a professional social media influencer – a public communicator with a large online following.

The speakers are real individuals and appear as recorded videos of themselves delivering the message. The informational script is identical across speakers and conditions to ensure that message content is constant across treatments, except for participants in the control group who do not receive the health message.

The experimental session consists of three main stages.

Pre-treatment survey

Participants complete a baseline questionnaire collecting demographic information, prior beliefs about vaccines, trust in institutions, social media use, information sources, knowledge of influencers, health-related behaviors, and social network information. The questionnaire includes the following categories of questions:

Administrative and participation information

session number assigned by the laboratory assistants

participant user ID

confirmation of consent and participation

Demographic and family background

year of birth

gender

role at the Athens University of Economics and Business (e.g., undergraduate student, postgraduate student, teaching staff)

department affiliation within the university

postgraduate program of study, where applicable

prefecture of origin in Greece

political ideology

mother's education and father's education

mother's occupation and father's occupation

family income category

The family background variables are collected using categorical response options. Parental occupations are recorded using broad occupational categories, including non-employment.

Baseline beliefs about vaccines
Participants report, on 0–10 scales ("not at all" to "completely"), the extent to which they believe that vaccines are:

effective at preventing pandemics and serious diseases

safe for individual health

important for their own health

important for public health

Trust in health-related institutions and information sources
Participants report their level of trust, on 0–10 scales, in:

conventional medicine and surgery

healthcare professionals

public health authorities

information obtained from social media

Social media use
Participants report their use of social media through several measures:

frequency of use, recorded on a 4-category scale: never; rarely (no more than once a week); often (more than once a week); every day or almost every day

time spent on social media on a typical day, recorded on a 6-category scale: less than 30 minutes; 30–59 minutes; 1–2 hours; 2–3 hours; 3–5 hours; more than 5 hours

main purpose of social media use, including whether it is used mainly for entertainment, information/news, or other purposes

Source of information
Participants are asked where they usually obtain information and news, including whether social media is their main source of information versus other sources. These variables are used to distinguish individuals who primarily rely on social media for information from those who rely more on traditional or other sources. This distinction is also reflected in the heterogeneity analyses described in the presentation materials.

Knowledge and familiarity with influencers
Before treatment, participants are asked about a set of well-known Greek influencers and public figures. For each person, they report:

familiarity, measured on a 4-point scale ranging from "I do not know this person" to "extremely familiar"

overall opinion, measured on a 5-point scale ranging from -2 (very negative) to +2 (very positive)

Health-related behaviors
Participants report:

smoking behavior during the last 30 days

physical exercise during the last 30 days

These variables are collected as ordered categorical measures of recent behavior.

Vaccination-related attitudes and past behavior
Participants answer baseline questions on their vaccination-related attitudes and prior behavior. In the follow-up survey, all participants are asked whether they are more willing to get vaccinated than before and whether they have received any additional vaccines since the main study period.


Social network information
Participants are asked to list up to 10 friends who also attend the Athens University of Economics and Business. For each listed friend, the survey collects:

first name and surname

time spent together in a typical university week outside class, measured on a 7-category scale from 0 hours to more than 20 hours

type of relationship, measured on a 4-category scale: mainly social/personal; mainly academic; both but mostly social; both but mostly academic

closeness to the friend, measured on an ordered response scale

Questions related to the evaluation of the speaker, evaluation of the message, perceived credibility of the messenger, and willingness to discuss the issues raised in the intervention are asked only after the informational exposure and therefore only for participants assigned to the Video or VR treatment groups.


Informational exposure

Participants are exposed to the public health message delivered by the speakers according to their assigned medium condition (VR or Video). Participants in the control group watch a neutral video lasting approximately 1.5 minutes.

Post-treatment survey

Immediately after the informational exposure, participants complete a questionnaire measuring the main outcomes of interest, including trust in vaccines, trust in the healthcare system, willingness to discuss vaccination-related topics with others, evaluation of the message and the speaker, and perceived credibility of the speaker.

For participants in the VR condition, the system also records behavioral engagement measures including eye-tracking and gaze direction. These measures allow the study to examine mechanisms related to attention and engagement during the informational exposure.

Participants receive a fixed participation payment and are entered into a lottery to win several Apple products.

Two months after the laboratory session, participants are contacted to complete a follow-up survey. The follow-up survey collects information on participants' willingness to vaccinate and their self-reported vaccination status, allowing us to examine whether the effects of the informational intervention persist and translate into vaccination intentions and behavior over time.

Each session will be randomly assigned to one treatment arm. All participants to a session will receive the same treatment. Within session, those participating to those sessions receiving the information treatment (either VR or Video) will be randomized into one of the 4 speakers: Male Scientist, Female Scientis, Male Influencer, Female Influencer.

Experimental sessions, as each session will see the participants receiving the same treatment.

Yes

Randomization occurs at the individual participant level. The study therefore does not involve clustered assignment. The planned sample is approximately 1,000 individual participants (clusters of size 1).

The planned number of observations is 1,000, although we will try to collect more based on funding availability.

Approximately 333 participants in Control, 333 participants in Video, and 333 participants in VR. The primary treatment assignment is across three session-level arms: Control, Video, and VR. The presentation materials describe the treatment arms as VR, Video, or Control.