Google Trends: opportunities and limitations in health and health policy research

IntroductionGoogle dominates the market for internet search engines and isso pervasive that the term “to Google” has entered everyday usein a way that none of its competitors has. In Europe it is used in85% of internet searches [1] while in the US, it accounts for 65%[2]. In 2012, Google handled approximately 1.2 trillion searchesglobally, or 3.3 billion searches per day [3]. Although more recentdata are difficult to obtain because of commercial confidentiality,it has been estimated that the total number rose to about 2 tril-lion in 2018. In an era where web searches and transactions arerecorded instantaneously, this activity generates a massive volumeof data whose uses are often unexpected and virtually limitless.Every search that is undertaken, and every page that is viewed, istracked. Consequently, Google itself, along with many online con-tent providers, such as Amazon, make extensive use of these data,tailoring advertisements and the results of searches to each user’sbrowsing history.While individuals search for many things online, such as con-sumer goods and services, or practical information (such as openinghours or travel timetables), there is also significant search activityrelated to health concerns. According to the Pew Internet and Amer-ican Life Project, 80% of Internet users in the US have searched for∗Corresponding author.E-mail address: vishal arora@hms.harvard.edu (V.S. Arora).a health-related topic online, ranging from mental health, immu-nizations to sexual health information [4].Health and health policy researchers are also starting to takenote of the potential of these data. A PubMed search for “GoogleTrends” or “Google Insights” (previous version of Google TrendsTM)revealed an over 20-fold increase in original research articles orresearch letters using Google TrendsTMfrom 2009 to 2018 (Fig. 1).While much of this information is kept secret by online providers,other elements are available to anyone. This paper offers a generalguide to how Google collects and shares search engine data, howtheir data has been used in the past, and how health and healthpolicy researchers can make greater use of these data in the future.