The numbers behind the calculations

    Health benefits

    1 hour exercise/week = 2*52/24 = 4 days longer life/year_lived
    2 hours life/hour exercise/week * 52 weeks/year_lived * 1/24 days/hour

    1 cigarette/day = -3.0 days life/year
    -12 min life/cigarette/day * 365 days/year * 1/60 hours/min *
    From American Cancer society (Science claims 5 minutes/cigarette)

    To calculate life expectancy
    years-won = days-won/365
    modified-life-expectancy = life-expectancy * (1 + years-won)

    Hazards

    1,000 miles/year driven = -.00365 days life/year
    10^-8 deaths/mile/year * 1,000 miles/year * 365

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    ungar@cis.upenn.edu