Internet Search Data and Issue Salience: The Properties of Google Trends as a Measure of Issue Salience

This article examines the conditions required for using Internet search data as measures of aggregate issue salience. Internet data have clear advantages over survey data in terms of cost, availability and frequency. These advantages have led the media and some researchers to use Internet search data as proxies for public opinion. However, these analyses do not present systematic evidence that search data tell us about the general public's views rather than those of an unrepresentative subset. This article outlines a general method for assessing the validity of search data against existing measures, including content validity and criterion validity. To this end, weekly Google search data are tested against Gallup's “most important problem” question. The article finds the salience of four issues, fuel prices, the economy, immigration and terrorism, can be measured in the United States using search data. Weekly measures of issue salience are generated for these issues, from 2004 to 2010, for empirical analysis. The search indices performed less well outside of these domains.