I think Peter Puck is on to something here but my take on it is slightly different.
Instead of a powerplay efficiency being ranked as 1 for 5 in a game, would it not make more sense for the PP to be reported as 1 goal for every 10 minutes of PP time. Over a season this could then be averaged with better teams say scoring 1 goal for every 8:32min of PP time and weaker teams, 1 goal for every 11:24min as examples. This would eliminate such statistical untruths as reporting a 1.2 second PP as a true man advantage.
Same could be done for penalty kills. I also think that a 2-man advantage should have its own category.