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Today’s topic: Does playing baseball shorten your life?

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1 Today’s topic: Does playing baseball shorten your life?
Vol. 2, Number 1, September 15, 2012 MV Stats News Bringing multivariate data analysis and data visualization to your breakfast table Today’s topic: Does playing baseball shorten your life? Michael Friendly, Staff Reporter Filed: 7/21/2018 6:21 AM

2 Background A National Institute for Occupational Safety and Health study (Mar., 2012) found that professional football players (NFL) lived longer, on average, than the general population Surprising, but maybe not so much, since they are elite athletes and only the strongest, fastest and healthiest get to play Notice that does NOT say that playing pro football will make you live longer--- probably quite the opposite! And, is a comparison of pro football players with the general population at all reasonable or useful? What other factors are not controlled?

3 Enter the sport journalist
Bill Barnwell decided to compare NFL players to baseball players, also elite athletes   Baseball Football Qualifying Players , ,088 Alive , ,694 Deceased Mortality Rate % % Apparently a highly significant association, p = 0.004! library(vcd) fourfold(tab)

4 Enter the sport statistician
But: there is a basic problem here: Baseball players tend to be older than football players MLB and NFL players are not directly comparable! football baseball Technical note: this graph shows density estimates – optimally smoothed, much better than histograms

5 Models to the rescue! Fit logistic regression models, predicting Alive (0/1) from dummy variable for Sport Model1: Alive ~ Sport (ignoring age) Model2: Alive ~ Sport + Age (controlling age) Conclusion: Effect of sport disappears. It’s only the relative ages difference responsible for difference in mortality p= p=0.444 p<2-16

6 Lessons When you read “X causes Y,” the hairs on the back of your neck should stand up! Careful writers report “association,” not causality Always ask what has not been controlled or accounted for (age, sex, lifestyle, genetics,...) Only randomized trials or experiments can claim causal explanations... ... but only if all other confounders have been controlled for. References: Stats in the Wild blog, Aug. 23, 2012,


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