” In reducing injury maybe, and even then it isn't convincing.” well I was pretty convinced by those statistics, as well as by anecdotal evidence.
”But RTI (Road Traffic Incidents) are far more about the circumstances surrounding the incident, the behaviour of the individuals involved...,If helmets result in a greater likelihood of an Incident, then they may be more detrimental when compared to the injury they limit...”
First, RTIs aren’t the only type of incident that might involve children coming off their bike. And secondly, again anecdotal, but my observation locally from seeing swarms of teenagers cycling to the local secondary school, the ones who do see the need to wear helmets tend to be those who use the cycle paths and cycle sensibly. The ones who don’t see the need for helmets are the ones who swarm all over the road, dodging around cars, on and off the pavement, not signally or looking. And coming off, either due to being hit by a car or just due to reckless behaviour on the bike.
It really isn’t the case that they put a helmet on and then think they’re invincible and behave like idiots. If they think they’re invincible and prone to behaving like an idiot then they’re also not going to think they need a helmet!
The OPs problem is whether she can not only tell him he has to wear a helmet, but also convince him of the need to wear one so that he doesn’t take it off again when he’s out of sight.