Figure out where the advances have come from. I'm guessing CFIT would be #1. Research what created those reductions.
For CFIT reduction I'd credit - FMC's/map display. EGPWS. Training. Recent years GPS can do added to improving FMC/map accuracy.
Obviously technology advance, engineering and manufacturing goes into the advancement of the newer systems/technologies(FMC's, GPS, TCAS, engines, systems design, systems componenets, etc)