How is on time departure measured?

Have you ever been on a plane and heard the flight attendants encouraging people to stow their luggage and be seated quickly so the door can be closed? Airlines have several ways of calculating on time departures with one of the most popular being the time the door is closed. Another common method is the release of the brake. Of course neither of these has anything to do with whether the aircraft takes off on time. In general, it is considered that the airlines can control boarding and pushback from the gate, but cannot control take-off delays that occur between the gate and the runway so these aren’t counted against the airline when looking at performance statistics. For me, I’d rather look at arrival statistics since a late departure does not always equate to a late arrival!