The report was based on an analysis of how well US-based domains performed in 2018. For each major site, the researchers calculated the Search Visibility, a metric that relies on various factors—search rank for the URL, search rank for high-volume keywords, the number of times it is included in organic search results, etc.—to assess how well a domain is faring on Google's desktop organic search.
Many of the sites that had large increases in Search Visibility in 2018 were video-focused. Chief among them was Google-owned YouTube, which recorded a +79% jump.
Some health-related websites also had big Search Visibility gains last year.