Chalk this up to living and learning.

I was checking on-time performance for a particular DL flight using FlightStats.

I was encouraged to learn that the flight had a 100% on-time record for a two month period (8/15 thru 10/15).

Encouraged, but skeptical.

When I dug deeper, I found that the flight had only operated 1 time on that route during that period. And, that the flight number had been used on 5 different routes during that period.

Fortunately, I found that FlightStats provides data for airline, route, and time of day. This allowed me to get some sense of what performance for other DL flights in that time period on that route had been.

Any idea what the data mean when you are researching an itinerary on Delta.com, and you dig down deeply to find the on-time statistics for a particular flight? If flight DL 123 is shown to be on-time 75% of the time... over what period is the data accumulated? ... does the data only reflect the performance of that flight number on that route?