Did tattoos cause motorcycle accidents? Or, for that matter, did motorcycle accidents cause tattoos? The researchers suggested that a third (unmeasured) variable was in fact the cause of both: A...

Did tattoos cause motorcycle accidents? Or, for that matter, did motorcycle accidents cause tattoos? The researchers suggested that a third (unmeasured) variable was in fact the cause of both: A tendency to take risks and to be involved in flamboyant personal displays led to tattooing one’s body and to driving a motorcycle recklessly.