Thanks I'll pass that on too.
Anyone have anything else that actually shows statistics or some sort of evidence proving it. I know these show it and it completely makes sense to most but she really wants actual evidence found by some research
I doubt you will find research of this type. Like many issues, there simply isn't the funding to prove or disprove every possible risk. This one seems more like a common sense issue. For example, I doubt you will find independent, peer-reviewed and published research comparing the self-stabbing rate among kids in houses with unsecured drawers vs. those that have child-proof latches on drawers with knives in them. Plus, with carseats, there are other factors involved, like how well adjusted the harness was with or without the jacket. That's something almost impossible to determine after a crash. It's a risk, it's real, but there's probably not much proof in terms of actual evidence.
Coats aren't always a bad thing in a child seat. Where much of the risk comes in is if when you loosen the harness to accommodate the coat. One comparison is to leave the harness adjusted for the coat, then put the child in the harness without the coat. If the harness seems really loose, especially to the point to where the child could wiggle out of part of it, then it's down to common sense that there is a safety risk.