Honestly, my first thought with almost any study on stuff like this is, "did you control for economic status?"
It's always the same shit: people who play golf live longer? Yeah, if they can afford to play an expensive game that takes a half a day to complete, they probably have more money and free time and less physical strain or emotional stress than the wage-slaves sorting boxes and hoping to be asked to work overtime so they can buy their kids braces.
Jack Welch did not singlehandedly ruin capitalism. He was a symptom of the problems capitalism is designed to create.