Guess I was one of the 1 out of 200. Performed it on my Grandmother way back when. I was 16 when she had a massive heart attack in our back yard. Stopped breathing, no pulse, nothing. She was just staring at the sky with her eyes open. My brother and I did CPR on her for several minutes while we waited for the ambulance. Was probably only 5-8 minutes but seemed like forever. She lived for another 15 years. Long enough to see my kids born.
It may not be 100% but sometimes it does make a difference. Back then it was 5-1, I remember it changing to 10-1 and now I guess were up to 30-2.