The numbers behind the calculations

    Health benefits

    Exercise

    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

    Light exercise

    up to 6 brisk walks of 30 minute each (per month!) reduced death rate by 30% over sedentary twin

    more than 6 brisk walks per month decreased death rate by 44 percent

    (source: JAMA Feb 11, 1998, as reported in Phil Inq)

    Cigarettes

    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 for the health benefits

    years_won = days_won/365
    modified_life_expectancy = life_expectancy * (1 + years_won)

    Hazards

    Driving

    1,000 miles/year driven = -.00365 days life/year
    10^-8 deaths/mile/year * 1,000 miles/year * 365
    wearing seat belts reduces this by a factor of two

    To calculate life expectancy for the hazards

    Directly modify the life table calculations with the change in the chance of dying each year.

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