Why are journalists so bad with numbers?
Reader Joel Wiles passed on this example from a New York Times article on the aging of Japan's prison population:
Between 2000 and 2006, while the total population of Japanese 60 and over rose by 17 percent, inmates of the same age group swelled by 87 percent. In the country’s 74 prisons, the proportion of older inmates rose to 12.3 percent in 2006 from 9.3 percent in 2000, while the share of those in their 20s declined and in other age groups remained flat.
While the main reason behind the explosion in graying lawbreakers is the rapid aging of Japan’s population, the rates have far outpaced the increase of older people in the general population.
Between 2000 and 2006, while the total population of Japanese 60 and over rose by 17 percent, inmates of the same age group swelled by 87 percent. In the country’s 74 prisons, the proportion of older inmates rose to 12.3 percent in 2006 from 9.3 percent in 2000, while the share of those in their 20s declined and in other age groups remained flat.
Japan’s rates are much higher than those in the West. America’s prisons — where those 55 years and over are categorized as elderly — are also graying. But such prisoners accounted for only 4.6 percent of the total prison population in the United States in 2005, according to the federal Bureau of Justice Statistics.
The phrase "Japan's rates are much higher than those in the West" falsely suggests that more elderly people are in prison in Japan than the US. However, while a higher percentage of prisoners in Japan are elderly, the proportion of the population that is both elderly and incarcerated is much greater in the US due to our dramatically higher incarceration rate (PDF). This is a classic example of what is known as the "base-rate fallacy." Can we get a statistical ombudsman or something?
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