I've started and erased a reply to this thread about three times now
The thing is, a harnessed seat is not a magical cure to all crashes. Logically, we think a 5 point harness is a safer option than a three point seatbelt that fits properly with the use of a booster, but I don't think we have the data to back that up yet. What we DO know is that a 5 point harness is better at keeping a child in the proper position, so from that perspective, a properly positioned child in a 5 point harness IS safer than a child who is out of position in a three point harness. That's why for younger heavier children we recommend a 5 point...not because 5 points are superior, but because young children frequently lean out of position, sleep in the car, are easily distracted, etc etc. For mature children who will stay in position, I honestly don't know how much additional protection, if any, a 5 point harness grants.
There can be other factors to consider as well, like space for other children in the car, budget, the skill level of the installer/caregiver. I guess what I'm trying to say is I honestly don't think getting everyone to put their 50 pound kids in harnesses would necessarily be a good thing in all cases. I agree, for those who truely need them, I wish more knew the option was available. But, for a child over 40 pounds who sits properly, a booster is not an unsafe option, and for all we know it may not even be a less safe option. That's why CHOP collects the exhaustive data that they do, to answer those questions, and make some good come out of something so tragic.