SUPPLEMENTARY INFORMATION

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1 In the format provided by the authors and unedited. SUPPLEMENTARY INFORMATION VOLUME: 1 ARTICLE NUMBER: 0056 Online Supplement On the benefits of explaining herd immunity in vaccine advocacy Cornelia Betsch 1,2,, Robert Böhm 3, Lars Korn 1,2 & Cindy Holtmann 1 1 Center for Empirical Research in Economics and Behavioral Sciences, University of Erfurt, Erfurt, Germany 2 Media and Communication Science, University of Erfurt, Erfurt, Germany 3 School of Business and Economics, RWTH Aachen University, Aachen, Germany * Correspondence: Cornelia Betsch, University of Erfurt, Nordhäuser Str. 63, Erfurt, Germany Phone: , Fax: , cornelia.betsch@uni-erfurt.de NATURE HUMAN BEHAVIOUR DOI: /s

2 Supplementary Figures Supplementary Figure 1. Dendrogram based on cluster analysis. NATURE HUMAN BEHAVIOUR DOI: /s

3 Supplementary Figure 2. Conceptual diagram of the tested multiple mediation model. Both perceived risk of the disease and collectivism are significant mediator variables, whereas perceived risk of vaccination is not. For statistical tests see Supplementary Table 8. NATURE HUMAN BEHAVIOUR DOI: /s

4 Supplementary Tables Supplementary Table 1: Cultural differences. The table provides the indicators used to create and validate the cultural clusters and the indicator of vaccine confidence used as a covariate. Germany (n = 379) Hong Kong (n = 136) India (n = 145) Netherlands (n = 18) South Korea (n = 718) USA (n = 650) Vietnam (n = 61) Cluster analysis variables Validation variables Hofstede s individualism Income Health system quality AICS collectivism* AICS individualism Tightness Vaccine confidence Note. Individualism: The high side of this dimension, called individualism, can be defined as a preference for a loosely-knit social framework in which individuals are expected to take care of only themselves and their immediate families. Its opposite, collectivism, represents a preference for a tightly-knit framework in society in which individuals can expect their relatives or members of a particular in-group to look after them in exchange for unquestioning loyalty. A society s position on this dimension is reflected in whether people s self-image is defined in terms of I or we. 1,2 Income: Gross national income per capita, purchasing power parity (international dollars in thousand), Health system quality: Detection rate for all forms of tuberculosis in percent. The number of new and relapse tuberculosis cases notified to WHO in a given year, divided by WHO s estimate of the number of incident tuberculosis cases for the same year 4,5. AICS collectivism: Strong sense of duty to group, relatedness to others, seeking others advice, harmony, and working with the group. ( 6, p. 52). AICS individualism: Valuing personal independence, which includes self-knowledge, uniqueness, privacy, direct communication, and competitiveness. ( 6, p. 52). Tightness: Strength of social norms and tolerance of deviant behavior. ( 7, p. 1101), within a country. Vaccine confidence: Percentage of participants agreeing totally or partially with the sentence: Overall I think vaccines are safe on a 5-point scale with higher ratings indicating higher agreement. Data result from the 67-country State of Vaccine Confidence study 8. * As assessed in the present study, see Supplementary Methods. NATURE HUMAN BEHAVIOUR DOI: /s

5 Supplementary Table 2: Analyses of variance predicting vaccination intention by vaccination rate, cultural background, and communication of herd immunity. Predictor High contagious disease Low contagious disease F-value p-value ηp 2 F-value p-value ηp 2 Vaccination rate (A) < Cultural background (B) < < Communication of herd immunity (C) < A*B A*C B*C A*B*C Note. N = 1,962. Dependent variable: Intention to vaccinate (0 100). Vaccination rate: 0 = low, 1 = high. Cultural background: 0 = Eastern countries, 1 = Western countries. Communication of herd immunity: 0 = Control (not communicated), 1 = Communicated. ηp: 2 Effect size partial eta-squared provided when >.001. NATURE HUMAN BEHAVIOUR DOI: /s

6 Supplementary Table 3. Analyses of variance predicting vaccination intention by vaccination rate, cultural background, and communication of herd immunity (corresponding to Supplementary Table 2, including n = 145 Indian participants as part of the Eastern cultural background). Predictor High contagious disease Low contagious disease F-value p-value ηp 2 F-value p-value ηp 2 Vaccination rate (A) < Cultural background (B) < < Communication of herd immunity (C) < A*B A*C < B*C A*B*C Note. N = 2,107. Dependent variable: Intention to vaccinate (0-100). Vaccination rate: 0 = low, 1 = high. Cultural background: 0 = Eastern countries, 1 = Western countries. Communication of herd immunity: 0 = Control (not communicated), 1 = Communicated. ηp: 2 Effect size partial eta-squared provided when >.001. NATURE HUMAN BEHAVIOUR DOI: /s

7 Supplementary Table 4. Analyses of variance predicting the change in vaccination intentions relative to control condition by vaccination rate, cultural background, communication content, and communication format. Predictor High contagious disease Low contagious disease F-value p-value ηp 2 F-value p-value ηp 2 Vaccination rate (A) Cultural background (B) < Communication content (C) Communication format (D) A * B A * C A * D B * C B * D < C * D A * B * C A * B * D < A * C * D B * C * D A * B * C * D < Note. N = 1,543. Dependent variable: Intention to vaccinate, mean centered at values in the structurally equivalent control condition ( ). Vaccination rate: 0 = low, 1 = high. Cultural background: 0 = Eastern countries, 1 = Western countries. Communication content: 0 = Individual benefit, 1 = Social benefit. Communication format: 0 = Text, 1 = Interactive simulation. ηp: 2 Effect size partial eta-squared provided when >.001. NATURE HUMAN BEHAVIOUR DOI: /s

8 Supplementary Table 5. Analyses of variance predicting the change in vaccination intentions relative to control condition by vaccination rate, cultural background, communication content, and communication format (corresponding to Supplementary Table 4, including n = 145 Indian participants as part of the Eastern cultural background). Predictor High contagious disease Low contagious disease F-value p-value ηp 2 F-value p-value ηp 2 Vaccination rate (A) Cultural background (B) < Bottom line (C) Communication format (D) A * B A * C A * D B * C B * D C * D A * B * C A * B * D A * C * D B * C * D A * B * C * D Note. N = 1,693. Dependent variable: Intention to vaccinate, mean centered around value in the structurally equivalent control condition ( ). Vaccination rate: 0 = low, 1 = high. Cultural background: 0 = Eastern countries, 1 = Western countries. Communication content: 0 = Individual benefit, 1 = Social benefit. Communication format: 0 = Text, 1 = Interactive simulation. ηp: 2 Effect size partial eta-squared provided when >.001. NATURE HUMAN BEHAVIOUR DOI: /s

9 Supplementary Table 6: OLS-Regression predicting vaccination intention by vaccination rate, Hofestede s individualism, and communication of herd immunity (corresponding to Supplementary Table 2, but using Hofstede s country values of individualism instead of a dichotomous Eastern/Western countries distinction). Predictor B SE p-value Intercept <.001 Vaccination rate (A) <.001 Hostede s Individualism (B) <.001 Communication of herd <.001 immunity (C) A * B A * C B * C <.001 A * B * C Note. N = 1,961. Dependent variable: Intention to vaccinate (0-100). Predictor variables are z-standardized. The regression analysis with continuous country values of individualism as predictor (as opposed to the East-West classification) also shows that intervention was particularly effective in individualistic countries and was weaker in collectivistic countries. Data is for the less contagious disease only. NATURE HUMAN BEHAVIOUR DOI: /s

10 Supplementary Table 7: Analyses of variance predicting vaccination intention by vaccination rate, cultural background, and communication of herd immunity (corresponding to Supplementary Table 2, additionally controlling for age, gender, income, quality of the health system and vaccine confidence). Predictor High contagious disease Low contagious disease F-value p-value ηp 2 F-value p-value ηp 2 Vaccination rate (A) < Cultural background (B) < Communication of herd immunity (C) A * B A * C B * C A * B * C Age Gender Income < < Health system quality < < Vaccine confidence < < Note. N = 1,962. Dependent variable: Intention to vaccinate (0-100). Vaccination rate: 0 = low, 1 = high. Cultural background: 0 = Eastern countries, 1 = Western countries. Communication of herd immunity: 0 = Control (not communicated), 1 = Communicated. Age: Participant age in years. Gender: 1 = man, 2 = woman. Income: Gross national income per capita, purchasing power parity (international dollars in thousand), 2015 (country value) 3. Health system quality: Detection rate for all forms of tuberculosis in percent. The number of new and relapse tuberculosis cases notified to WHO in a given year, divided by WHO s estimate of the number of incident tuberculosis cases for the same year (country value). 4,5 Vaccine confidence: Percentage of participants agreeing totally or partially with the sentence: Overall I think vaccines are safe on a five-point scale with higher ratings indicating higher agreement. Data result from the 67-country State of Vaccine Confidence study (country values) 8. ηp: 2 Effect size partial eta-squared provided when >.001. NATURE HUMAN BEHAVIOUR DOI: /s

11 Supplementary Table 8: Multiple mediation model. Regression paths Path a Path b Indirect effect a * b Proposed mediator BC 95 % CI B SE p B SE p B SE Lower Upper Collectivism < Risk disease < Risk vaccination < Note. N = 1,962. Path a: Cultural background (0 = Eastern countries, 1 = Western countries) on proposed mediator. Path b: proposed mediator on vaccination intention (controlling for cultural background). BC 95 % CI: Bias corrected 95 % confidence interval with lower and upper border, based on 10,000 bootstrap resamples; CIs that do not contain zero indicate a significant indirect effect with p <.050. NATURE HUMAN BEHAVIOUR DOI: /s

12 Supplementary Notes Cluster Analysis As a psychological variable we used Hofstede s country-specific values of individualism 2. The values were obtained from Hofstede s work and each country was assigned the respective value. As the countries also differ by gross income per capita, we included income as a second clustering variable. Finally, as an indicator for the quality of the health systems, we included the tuberculosis detection rate. The World Health Organization uses a wide range of variables to assess the quality of health systems (overview see 9 ). We selected tuberculosis detection rate, as higher rates are an indicator of better service coverage and therefore express availability of and access to health services. Moreover, it was available for all countries of interest. A hierarchical cluster analysis calculates the squared Euclidian distances between the respective variables. It created the clusters of countries based on proximity. Within one cluster, the members of the cluster are as similar as possible to others within their group (high within-group homogeneity) and as different as possible to those in other groups (low between-group homogeneity) ( 10, p. 330). In this hierarchical cluster analysis, Germany, the Netherlands, and the USA constitute a cluster (Western countries henceforth); the second cluster comprises South Korea, Vietnam, and Hong Kong (Eastern countries henceforth). India becomes a third cluster. In order to further explore the validity of the two ontained clusters comprising Eastern vs. Western countries, we analysed whether the clusters differ on the cultural scales that we assessed on an individual level in the course of the study (see Supplementary Methods). They measure individualism, collectivism and tightness on a scale ranging from 1 to 6, with higher values expressing greater levels of individualism, collectivism, and tightness, respectively. As expected based on theory 11 14, participants from Eastern countries scored higher on measured collectivism than participants from Western countries (M East = 4.06, SD = 0.61 vs. M West = 3.73, SD = 0.77, analysis of variance (ANOVA): F(1, 1960) = , p <.001, η 2 =.050). There was a smaller difference regarding individualism (M East = 4.25, SD = 0.60 vs. M West = 4.30, SD = 0.65, F(1, 1960) = 3.32, p =.07, η 2 =.002). Tightness describes the strength of obedience to social norms and the tolerance of the violation of norms, and is usually higher in Eastern compared to Western societies 7. In line with these previous findings, participants from Eastern countries were tighter than those from Western countries (M East = 4.10, SD = 0.59 vs. M West = 3.96, SD = 0.66, F(1, 1960) = 24.65, p <.001, η 2 =.012). NATURE HUMAN BEHAVIOUR DOI: /s

13 Supplementary Methods The following gives details about how the measured constructs were operationalized. Individual-level individualism and collectivism At the very beginning of the study, individualism and collectivism were assessed with the Auckland Individualism Collectivism Scale (AICS) 6. The scale uses 26 items such as, I consider myself as a unique person separate from others or Before I make a major decision I seek advice from people close to me. On a six-point scale, participants indicate whether they act in the described way, 1= almost never and 6 = almost always. Cronbach s alpha of the individualism scale was α =.82 and α =.79 for collectivism. In addition, the strength of social norms and tolerance of the violation of norms within a country was measured with the Tightness-Looseness Scale 7. The scale comprises six items such as There are many social norms that people are supposed to abide by in this country or People in this country agree upon what behaviours are appropriate versus inappropriate in most situations. Participants express their level of agreement on a six-point scale, 1 = strongly disagree to 6 = strongly agree. Cronbach s alpha was α =.57. For mean values, see Supplementary Table 1. For differences between cultural backgrounds, see Supplementary Notes. Scenario recall and manipulation check After participants had read the scenario, a recall test ensured that they understood the parameters given in their scenario (probability of infection, of vaccine-adverse events, and vaccine uptake). In the case of failed recall, the scenario was presented up to two more times. Only participants who passed the scenario recall could proceed. A second manipulation check examined the recall of the herd immunity information. The respondents, except for those in the control condition, were asked to recognise the condition-dependent bottom line in a single-choice task. The task offered literal quotes of the individual benefit message, social benefit message, both, or don t know as options. Dependent measure Vaccination intention was the main outcome measure and was assessed for both hypothetical diseases ( If you had the opportunity to get vaccinated against [name of the disease] immediately, what would you do? ) on a 100-point scale (1= I would definitely not get vaccinated to 100 = I would definitely get vaccinated ). Perceived risk The participants rated both the perceived riskiness of vaccination ( How risky do you judge the vaccination against [name of the infection] to be? ) and the riskiness of an infection ( How risky do you judge a [name of the infection] infection to be if you do not get vaccinated? ) with the help of a slider-measure [0 100]. NATURE HUMAN BEHAVIOUR DOI: /s

14 Supplementary References 1. Hofstede, G. H. Cultural Dimensions (2016). URL cultural-dimensions.html. 2. Hofstede, G. H., Hofstede, G. J. & Minkov, M. Cultures and organizations : software of the mind (McGraw-Hill, 2010), 3rd edn. 3. World Bank. Gross national income per capita 2015, Atlas method and PPP (2015). URL 4. WHO. Global tuberculosis report 2015 (2015). URL /191102/1/ _eng.pdf?ua=1. 5. World Bank. Tuberculosis case detection rate (%, all forms) (2016). URL worldbank.org/indicator/sh.tbs.dtec.zs. 6. Shulruf, B., Hattie, J. & Dixon, R. Intertwinement of individualist and collectivist attributes and response sets. TJ. Soc. Evol. Cult. Psychol. 5, (2011). 7. Gelfand, M. J. et al. Differences between tight and loose cultures: a 33-nation study. Science 332, (2011). 8. The Vaccine Confidence Project. State of vaccine confidence 2016: Global insights through a 67-country survey (2016). URL 9. WHO. Global reference list of 100 Core health indicators. working version 5 (2014). URL GlobalRefListCoreIndicators_V5_17Nov2014_WithoutAnnexes.pdf. 10. Clatworthy, J., Buick, D., Hankins, M., Weinmann, J. & Horne, R. The use and reporting of cluster analysis in health psychology: A review. Brit J Health Psych 10, (2005). 11. Hofstede, G. Culture s consequences: Comparing values, behaviors, institutions and organizations across nations. (Sage Publications, 2001). 12. Triandis, H. C. & Gelfand, M. J. Converging measurement of horizontal and vertical individualism and collectivism. J. Pers. Soc. Psychol. 74, (1998). 13. Oyserman, D., Coon, H. M. & Kemmelmeier, M. Rethinking individualism and collectivism: Evaluation of theoretical assumptions and meta-analyses. Psychol. Bull. 128, 3 72 (2002). 14. Markus, H. R. & Kitayama, S. Culture and the self: Implications for cognition, emotion, and motivation. Psychological Review 98, (1991). NATURE HUMAN BEHAVIOUR DOI: /s

Supplementary appendix

Supplementary appendix This appendix formed part of the original submission and has been peer reviewed. We post it as supplied by the authors. Supplement to: Korn L, Betsch C, Böhm R, Meier NW. Drawbacks