Also, the traditional measure is skewed by shorted penalties when one team takes a penalty while on the power play. If the penalties happen 10 seconds apart, for example, the accounting for each team will be the same for the 10 second power play as if they each had a full 2 minute power play.

Similarly, a power play which fails to score on a 5 minute power play is treated the same as failing to score on a 2 minute power play. So what if we measured instead by goals per 2 min of power play? (Or how many seconds of power-play time was required for each goal scored?)