The merge rate is the % of pull requests merged out of every pull request opened during this time frame and that is no longer opened.
This is the average number of reviews per pull request. A review could be of state: commented, requested_changed, or approved.
The pull request length is always composed of two parameters: the number of lines added and the number of lines deleted compared with the base branch.
The development time is the time from the first commit to a pull request ready for review. If we can't find an event "ready for review", we will use the first review request as the end of the development time, if then we can't find any review request event, we will use the time of the first review.
The review time starts at the end of the development time and ends once the pull request is merged. The review time is composed of three periods: the response time (or pickup time), the rework time, and the completion time.
The cycle time is the sum of development time and review time. It is the time from the first commit to merge.
The response time is the time from the beginning of the review time to the first review. It is a measure to understand how much time an engineer waits on average before receiving his first review.
The rework time is the time between the first non-approved review (either a 'commented' or a 'requested_changes' review) to the last approved review.
The completion time is the time between the last approved review to the pull request being merged.