I preface this by saying my experience is obviously entirely anecdotal, but while I've sadly known several who have been seriously injured in bike crashes over the last couple of years, none of those incidents occurred on a group ride. I actually think on the whole group riding can be safer than individual riding, chiefly because you're more visible to motorists and they're generally less likely to pull something stupid that can lead to serious injury, or even death, for you.

Also, it's tougher for a driver to flee an incident involving a group ride for a variety of reasons. I know someone who is currently recovering from serious injuries after being hit by a car on a training ride in the spring and if he hadn't been in a popular area and had a number of witnesses to the crash, the whole incident could have devolved into a "he said, she said" thing, making it much more difficult for him.

Without any data, my bet is that you're right that you're significantly less likely tobe hit by a car on a group ride.

However, the odds of bike on bike bike collisions goes way up, obviously. So the chance of getting killed on balance is likely lower, but the chance of serious injury from a fall, such as a broken collar bone, fractured pelvis, traumatic brain injury, goes up.

None of this is meant to say that I think group riding is unreasonably unsafe. The point is that in a group ride, your actions can affect the safety of others, and have very negative consequences. Hence, it's incumbent on every member of the group to ride safely.