To establish a baseline, groups of snipers and competition shooters were tested. Weapon Pointing (aiming) Error, the ability of a shooter to hold his or her aim on target, was obviously a key test.
According to their tests, the standard deviation of aiming error for the best, formally-trained operational snipers was three times worse than tested High Power and Long Range competition shooters sufficiently skilled to compete successfully in national level match competition at Camp Perry and the like. In fact, the worst competition shooters tested were as good or better than the best snipers in basic holding and shooting fundamentals.
Competition shooters strive for excellence, not just competence:
A recently retired friend of mine was one of the better shooters in his police department, and had done well at a number of law enforcement training events and qualifications, including SWAT schools and the like. In his peer group, he was pretty good. When I got him a slot in a class with some folks outside his peer group, however, his understanding of what skill with a handgun was changed dramatically. A relatively small group of enthusiasts exhibited skill that was well above anything he’d ever encountered in uniform up to that point. He told me that even the best law enforcement shooters he knew of would struggle to try and keep up with some of the poorer performers in that small group. It’s not surprising… because the enthusiasts were pursuing excellence, and most of the law enforcement world is focused on competence.