I suspect the subway number would come out to a different number, when applied to the actual ridership statistics(I dont know if closer or further from the school statistic though) . For example, you know the number of rides, but not the actual number of riders. A single trip could wind up being multiple swipes(rides) of the metro card. Or another example would be someone who needed to make multiple transfers would spend more time on the platform than someone riding a single line from point A to B. Some people might take 5 trips, while others 1 etc. But then the probabilities likely get pretty complex to factor in these things.
Also getting pushed off the platform is not the only bad thing that can happen on the subway or platform. The subways are so safe
that they wanted a special prosecutor just for crimes on the subway. Granted that's mostly theft, but violent crimes do also occur.