Digital contact tracing smartphone applications (apps) can mitigate the spread of COVID-19 through exposure notification.1-4 However, their success requires widespread use. We examined the effectiveness of low-cost behavioral interventions (ie, nudges) in increasing downloads of Pennsylvania’s COVID Alert PA app. Specifically, we explored the effectiveness of 2 nudges5,6 on 39 937 individuals, one nudge displaying a descriptive social norm (vs not) and another framing the benefit of downloading for others (vs self).
In this randomized clinical trial, 39 937 Pennsylvania members of Independence Blue Cross were randomly assigned to receive 1 email in a 2 (focus on self vs focus on others) × 2 (social norm vs no social norm) design (Table 1). In the focus-on-self condition, the message stated the benefits of the app for participants as follows: “It can help you determine where and when to get testing, and how to get care if you need it.” In the focus-on-others condition, the message stated the benefit to others as follows: “It can help you reduce your risk of unknowingly spreading the virus to your friends, family, and larger community.” In the social-norm condition, the message stated, “Over 650 000 Pennsylvanians have already downloaded the app!” This statement was absent in the no-social-norm condition. At the bottom of each email, a link directed participants to a site to download the app (eMethods in Supplement 1). This study was exempt from University of Pennsylvania Institutional Review Board approval and received a waiver for informed consent because the study involved minimal risk to the participants. The full trial protocol appears in Supplement 2. This study followed the Consolidated Standards of Reporting Trials (CONSORT) reporting guideline.
We conducted 1 logistic regression estimating our primary outcome, clicks on the download link contingent on opening the email (42.3% opened), from 2 dummy variables representing conditions and a similar regression with the interaction term in the model. A 2-sided, α = .05 was considered statistically significant. Both were intent-to-treat analyses using Stata, version 15.1 (StataCorp LLC).
Of 39 937 participants, the mean (SD) age was 46.5 (13.2) years and 41.6% were male. Findings show participants were significantly more likely to click on the link when a social norm was absent (vs present) (no social norm = 13.3% vs social norm = 8.4%; unadjusted OR, 0.60; 95% CI, 0.54-0.66; P < .001) and when the message focused on the benefits to others (vs self) (focus on others = 13.0% vs focus on self = 8.7%; unadjusted OR, 0.63; 95% CI, 0.57-0.69; P < .001).
The main effects were qualified by a significant 2 (focus on self vs focus on others) × 2 (social norm vs no social norm) interaction (unadjusted OR, 2.16; 95% CI, 1.76-2.64; P < .001). When the message focused on the benefit to others, including a social norm significantly decreased clicks on the link (focus on others, no social norm = 17.7% vs focus on others, social norm = 10.9%; unadjusted OR, 0.43; 95% CI, 0.38-0.49; P < .001; Table 2). When the message focused on the benefit to self, including a social norm did not have a significant effect (focus on self, no social norm = 11.4% vs focus on self, social norm = 10.7%; unadjusted OR, 0.93; 95% CI, 0.80-1.08; P = .32). The most effective nudge focused on the benefits for others without a social norm, leading to a 6.0% or greater increase in clicks relative to other conditions.
The findings of this randomized clinical trial reveal the effect of social norm and self (vs other) nudges on downloads of a contact tracing app. One limitation of this study was its reliance on an indirect measure of downloads, that is, clicks to a website to download.
Future research should explore the mechanism and whether the effect generalizes to other locations/apps. One possibility is that when focusing on the benefit to others, downloading the app is perceived as a group goal, which may be motivating with no social norm. However, when a norm signals many already contributed to the goal (without a specific target), people may believe their individual action is less needed. Overall, this research suggests that costless nudges can help reduce the spread of harmful viruses by increasing downloads of contact tracing apps, an important and urgent issue.
Accepted for Publication: October 30, 2021.
Published: December 23, 2021. doi:10.1001/jamanetworkopen.2021.40839
Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Sharif MA et al. JAMA Network Open.
Corresponding Author: Marissa A. Sharif, PhD, Marketing Department, Wharton School of the University of Pennsylvania, 3730 Walnut Ave, Philadelphia, PA 19104 (masharif@wharton.upenn.edu).
Author Contributions: Ms Bair had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Sharif, Dixon, Garzon, Gibson, Volpp.
Acquisition, analysis, or interpretation of data: Sharif, Bair, Gibson, Linn.
Drafting of the manuscript: Sharif, Dixon.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Sharif, Bair.
Obtained funding: Dixon, Volpp.
Administrative, technical, or material support: Sharif, Dixon, Garzon, Volpp.
Supervision: Sharif, Dixon.
Conflict of Interest Disclosures: Dr Volpp reported being a part owner of VALHealth, a behavioral economics consulting firm; receiving research funding from Hawaii Medical Services Association, Humana, CVS, WW, and Vitality/Discovery; and receiving personal fees from Tandigm, Lehigh Valley Medical Center, Vizient, and the Center for Corporate Innovation. No other disclosures were reported.
Funding/Support: This study was supported by the Pennsylvania Department of Health for research involving COVID Alert PA, the exposure notification app for the Commonwealth of Pennsylvania.
Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.
Trial Registration: ClinicalTrials.gov Identifier: NCT05080179
Data Sharing Statement: See Supplement 3.