This API aggregates top-level metrics associated with "propensity" events, events generated when users are scored using Machine Learning according to how likely they are to complete a given action (like subscribing).
The API uses the same request, response and limitations as for /traffic, except that that the only fields that can be aggregated are events and uniqueUsers where events is an implicit field.
events here is the number of times a user was scored. Note that this might be different than the number of pageviews for a site, for example if several propensity models are in use for the same site, or if the site is using autorefresh.