What would you set up to collect how many comments users posted to a webpage on your site? When a report is based on data from a large number of sessions, you may see the following notice at the top of the report: “This report is based on N sessions.”
Custom Metric is required to collect the number of comments users posted to a web page. Explanation: custom metrics can produce more flexible and more readable custom reports and as such are a convenient way to track your most important metrics.
I would set up a Google Analytics event tracking goal that counts the number of comments received on a given webpage. This would allow me to see how frequently people are posting comments and what the average number of comments per visitor is.