Boy; I wish I'd keep the numbers. Sporty you know, I have been in EMS since 1971 in one capacity or another. I have seen seat belt development from old simple lap belts. The vast majority of seat belt wearers have fared much better than their non-wearing counterparts but alas I have no numbers to back it up.
All I can offer is my opinion based on my observations and recollections. Like they say, seatbelts save lives!! Lead by example, wear yours too. Heck, you already paid for them when you bought the car.