Which of the following is a key performance indicator (KPI) for search engines?

The correct choice highlights Conversion Rate as a key performance indicator (KPI) for search engines because it directly measures the effectiveness of a website in turning visitors into customers or leads. In the context of search engine marketing, a high conversion rate indicates that the traffic generated from search engine results is relevant and successfully engaging users, leading them to take desired actions. This metric is crucial for assessing the overall performance of search campaigns and the quality of landing pages, making it an essential KPI.

While Return on Investment (ROI), Time on Site, and Bounce Rate can offer valuable insights into a website's performance, they serve different purposes. ROI measures the financial return of marketing efforts, which is broader than the specific performance implications of search engines alone. Time on Site evaluates user engagement, but does not necessarily correlate to successful outcomes unless coupled with conversion data. Bounce Rate assesses the percentage of visitors who leave after viewing only one page, which may indicate issues but does not directly inform about the conversion process itself. Thus, while all these metrics are important, Conversion Rate uniquely reflects the effectiveness of search engine traffic in achieving business goals.