Understanding vaccination resistance: Vaccine search term selection bias and the valence of retrieved information
Introduction
Growing apprehensions about the risks of vaccines among the general public [1] have been accompanied by more frequent outbreaks of vaccine-preventable disease [2], [3]. Concerns about vaccine safety lead some parents to postpone vaccination of their children, against the recommendation of their pediatrician, while other parents reject all vaccinations for their children [4], [5], [6]. These concerns motivate many parents to seek information about vaccines from other parents, traditional media, and the Internet [7]. A survey of providers found that fear of side effects presented in the media was the most common reason given by parents for refusing vaccines [8].
The Internet may be partially responsible for low child vaccination rates. Vaccination-refusing parents are more likely to have obtained information about vaccines from the Internet than parents who have their children vaccinated [8], [9]. Kata found that a reliance on Internet-based information is problematic due to the presence of inaccurate and deceptive online information [9]. Zimmerman and colleagues found that websites often erroneously link vaccinations to chronic diseases and adverse reactions [10], thereby proliferating vaccine myths. Myths perpetuated online undermine vaccination programs by lowering the public's perceived effectiveness and safety of vaccines [11], [12].
There is evidence of a selectivity effect in online vaccine information searches in which search terms varying in valence yield information that differs in accuracy and tone [13]. People often seek information to support existing beliefs [11], [14]. This confirmatory bias has also been found in online health information-seeking behavior [12]. In the domain of vaccination, a confirmatory bias is illustrated by both the pro-vaccine parent who searches “vaccination benefits” and the parent whose skepticism about vaccination leads to a search for “vaccination risks.”
The purpose of this study is to determine if online search strategies employing negative, neutral, or positive search terms lead to content that correspond with the valence of those terms. We know of no study that has investigated this question. We thus carried out a content analysis that addressed four broad research questions: (a) What vaccine myths are most likely to be perpetuated online? (b) How often do vaccination websites counter myths about vaccination safety and effectiveness? (c) Do websites that discuss vaccination make explicit recommendations about childhood vaccination, and if so, what are these recommendations? (d) Does the online information retrieved about vaccination differ depending on whether the search terms used are negative, neutral, or positive?
Section snippets
Search terms
Web searches were conducted on September 2, 2013, via the Google search engine (www.google.com), using three negative, three neutral, and three positive search terms for the base concepts “vaccine,” “vaccination,” and “MMR,” as shown in Table 1. These three terms were chosen because they are the most popular vaccine information search terms used, based on Google Trends data [15]. The term “immunization” was not selected for analysis because it did not appear as a popular search term on Google
Perpetuated vaccine myths
In total, 16.7% (n = 14) of websites spread myths about vaccination. More precisely, 6.0% (n = 5) of the 84 websites analyzed perpetuated one myth about vaccination, 2.4% (n = 2) perpetuated two myths, and 8.3% (n = 7) perpetuated three or more myths. The most commonly perpetuated myth was “children's vaccines cause autism” (9.5%, n = 8), followed by “children's vaccines cause other severe illnesses” (8.3%, n = 7). The other 13 myths were spread less frequently or not at all (Table 2).
Search term selectivity and myth perpetuation
For the 28 websites
Discussion
The findings from this study indicate that the valence of search terms a parent or others might use when investigating childhood vaccinations can dramatically affect what they find. Consider the parent who is concerned about vaccination safety and thus searches for information about vaccination risks. This vaccine-averse parent would encounter 3.6 times more vaccine myths per website than a parent who uses neutral terms, and 4.8 times more myths that the parent who searches for information
Acknowledgements
The authors thank George A. Barnett, Ph.D., April Li, and Meng Chen for their comments on this paper. We are grateful to Andrew Kulp and Christopher Boyle for their coding assistance and to two anonymous reviewers for insightful comments that improved this paper.
Conflicts of interest: The authors declare no conflict of interest in the research for this study.
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2021, VaccineCitation Excerpt :Our study found that these influencers gravitate towards search engines and platforms that return information and results that align with their views, a form of confirmation bias. Previous research documents this phenomenon, finding that including certain terms or keywords in search strategies return vastly different results [39,40]. Similarly, technologies are available, such as apps that allow parents to self-analyze their child’s genetic data from online ancestry site to uncover genetic susceptibilities to vaccines, to obtain medical exemptions from school-mandated vaccines.