The importance of context

The New York Times ran an article in today's paper describing the differences in methodology used to develop suicide rates for the military, and the methodology used to develop the rate for the civilian population. The Times says that Pentagon medical statisticians use

a total population figure that includes all Guard members or reservists who spent any period of time on active duty in a given year, even if it was only a few days. According to that approach, the total active military population was about 1.67 million for all of 2009, a review of Pentagon data shows.

But at almost any given moment, the United States military is much smaller than that. Another office of the Pentagon, the Defense Manpower Data Center, the personnel record-keeping office, used a total population number of about 1.42 million service members in 2009. That figure was calculated by including only National Guard and reserve troops who had been on active duty for at least six months in a given year.

Therefore, because the denominator is too large, the military has been understating the suicide rate. (You can find a reasonably explanation of calculation of a rate here.) Why is this important? Because when the military rate and the civilian rates are comparable, there's less of a problem.