If scheduled airlines carried 10 times as many passengers as commuter lines, the death rates would be roughly equal. We know that the first-year parents who consented were usually better off economically, and hence their children, if left untreated, were more likely to get polio than those whose parents didn't consent. The treatment lowered the risk of polio almost to the level of the children of non-consenting parents. This study was controlling for the confounding variables age and sex. This is the wrong conclusion to draw from the evidence.
Many people choose to stop smoking because they are getting sick.
Thus, stopping smoking was probably the effect, not the cause, of health problems. Additional problem Simpson's Paradox is at work here. The overall success rate is higher for Hope Hospital, but Mercy is more successful for each individual type of operation. For whichever particular type of operation we are getting, the success rate would be higher at Mercy. All rights reserved.