Thursday, June 18, 2009

Correlation is not causation

During a ten year period, the number of cancers for the population under the age of 25 in the affected county rose at a rate more than three times faster than that for the rest of the state; it rose from 18.5 cases to 23.4 cases per 100,000 people. In the rest of Michigan, the rate rose from 20.2 cases to 21.9 cases per 100,000 people.

Since there are about 50,000 people under the age of 25 living in this particular county, the normal number of cancers in people under 25 is an average of nine ...

The increase in the rate of cancer (18.5 to 24.3 cases per 100,000), as discussed in the health report, is based on three additional cases of cancer. This difference, 9 cancer cases versus 12 cancer cases, is not out of line of what we would expect based upon random variability. We would expect up to 17 in any given year.