Wednesday, September 28, 2011

Low-Hanging Fruit for the Cranky Analyst: Gross Misinterpretation of Statistics

The National Center for Education Statistics just put out a report on the employment experiences of new teachers. StudentsFirst grabbed the report and wrote a blog about it. They should have slowed down. I suggest that this fine organization hire some UM Ford School grads to help them with their statistical analyses.
The StudentsFirst blog says of the NCES report:
"Teachers making more than $40,000 were 3.7 times more likely to stay in the profession than those making less."
The NCES report says:
"Approximately 93 percent of beginning public school teachers who were earning less than $40,000 in 2008–09 remained teachers in 2009–10, and about 96 percent of beginning public school teachers who were earning $40,000 or more in 2008–09 remained teachers in 2009–10 (table 3). "
Hmmm, is 96% the product of 3.7 and 93%? Let me get my calculator.....(tap, tap, tap). Nope! That would imply that 355% of better-paid teachers stay on the job. There IS about a 3 percentage point difference in the share of low vs. high-earning teachers staying in teaching: 7% of those earning <$40K leave, compared to 4% of those earning >$40K. That's worth writing about!