Background: Google AdWords, the placement of sponsored links in Google search results, is a potent method of recruitment to Internet-based health studies and interventions. However, the performance of Google AdWords varies considerably depending on the language and the location of the target audience.
Objective: Our goal was to describe differences in AdWords performance when recruiting participants to the same study conducted in four languages and to determine whether AdWords campaigns can be optimized in order to increase recruitment while decreasing costs.
Methods: Google AdWords were used to recruit participants to the Mood Screener, a multilingual online depression screening tool available in English, Russian, Spanish, and Chinese. Two distinct recruitment periods are described: (1) "Unmanaged", a 6-month period in which ads were allowed to run using only the AdWords tool itself, with no human intervention, and (2) "Managed", a separate 7-week period during which we systematically sought to optimize our recruitment campaigns.
Results: During 6 months of unmanaged recruitment, our ads were shown over 1.3 million times, resulting in over 60,000 site visits. The average click-through rate (ratio of ads clicked to ads displayed) varied from 1.86% for Chinese ads to 8.48% for Russian ads, as did the average cost-per-click (from US $0.20 for Chinese ads to US $0.50 for English ads). Although Chinese speakers' click-through rate was lowest, their rate of consenting to participate was the highest, at 3.62%, with English speakers exhibiting the lowest consent rate (0.97%). The conversion cost (cost to recruit a consenting participant) varied from US $10.80 for Russian speakers to US $51.88 for English speakers. During the 7 weeks of "managed" recruitment, we attempted to improve AdWords' performance in regards to the consent rate and cost by systematically deleting underperforming ads and adjusting keywords. We were able to increase the number of people who consent after coming to the site by 91.8% while also decreasing per-consent cost by 23.3%.
Conclusions: Our results illustrate the need to linguistically and culturally adapt Google AdWords campaigns and to manage them carefully to ensure the most cost-effective results.
Keywords: Internet recruitment; Internet research; multinational; online; recruitment costs.