Chance News 59

Quotations

I wish I could say, well, I told people correlation doesn't equal causation back in 1989, so I don't have to say it again.

Joe Palca, NPR science correspondent, lamenting the lay public's continual lack of understanding of how science progresses; this appeared in an article by Julia Galef entitled "Uncertainty in Science, It's a Feature, Not a Bug," The Humanist, January-February 2010.

Submitted by Paul Alper

Calculating high school dropout rates

KC School District's dropout rate doesn't add up. Michael McShane, The Kansas City Star.

The Kansas City, Missouri school district had some amazing statistics to brag about.

The Kansas City School District recently announced a dropout rate of 5.9 percent. Compared with the dropout rate of 41.2 percent reported a year ago, it appeared as if the district was moving by leaps and bounds in the right direction to correct the problem.

These results, however, appear to be incorrect.

The Missouri Department of Education says when the Kansas City School District’s Class of 2009 started eighth grade in the fall of 2004 it had 2,629 members. When that class graduated this spring, 1,032 students earned diplomas. It doesn’t take a degree in mathematics to recognize that does not add up.

The calculation of a dropout rate is not too difficult.

It is a simple mathematical formula; take the total number of students who graduate and divide it by how many students started in eighth grade. If necessary, adjust that number for demographic movement trends and with a No. 2 pencil and a scientific calculator, anyone at home can estimate the graduation rate.

Here are the numbers you need for the calculation.

Let’s calculate it together. When those 2,629 eighth-graders were enrolled in the district, the total enrollment for the district was 26,968 students. When 1,032 members of that cohort earned diplomas there were 22,479 total students enrolled in the district.

If you don't account for migration, the graduation rate is 1032 / 2629 = 39%. Here's how to account for migration.

In that same period, the overall district enrollment declined by 16.65 percent, so it’s fair to reduce the number of eighth-graders to reflect that, which we can do by multiplying by 0.8335. After those calculations, the adjusted graduation rate of the district is really 47 percent.

Part, but not all of the discrepancy, can be accounted for by a change in time frame. The 5.9% represents an annual drop-out rate, not a rate across four years, a practice that Dr. McShane derides.

The district’s using that number as its dropout rate is the equivalent of your credit card company telling you the monthly rather than the yearly interest rate. It may make you feel better, but you’re still going to pay big.

Questions

1. How would you convert a yearly dropout rate to a four year dropout rate?

2. The adjustment for migration makes some assumptions. What are those assumptions? Are they reasonable?

3. Would it make sense to compute confidence limits for the dropout rate?

Submitted by Steve Simon

Ill health news

10 trends in health care journalism going into 2010
HealthNewsReview Blog
Gary Schwitzer

Schwizter is an associate professor at University of Minnesota School of Journalism & Mass Communication, and the publisher of Health News Review, a web site which monitors the accuracy of news stories related to medicine. The project is funded by the Foundation for Informed Medical Decision Making.

From the blog post referenced above we learn that "An updated look at the first 900 stories reviewed on HealthNewsReview.org shows that An updated look at the first 900 stories reviewed on HealthNewsReview.org shows that:

• 71% fail to adequately discuss costs
• 71% fail to explain how big (or small) is the potential benefit
• 66% fail to explain how big (or small) is the potential harm
• 66% fail to evaluate the quality of the evidence
• 60% fail to compare new idea with existing options

and as to television in particular, After 3.5 years and 228 network TV health segments reviewed, we can make the data-driven statement that many of the stories are bad and they're not getting much better."

With regard to the US Preventive Task Force's mammography recommendations,

"There was some excellent journalism done on the issue last week, but it was overwhelmed by and drowned out by the drumbeat of dreck shoveled out by many news organizations - including in much (not all) of what was provided on network TV." Further, vThe week was certainly a setback for the nation's understanding of science, of evaluation of evidence, of the potential harms of screening tests.v Much of this thanks to vThe public relations machinery of the American Cancer Society, the American College of Obstetrics and Gynecology - and other groups that opposed the USPSTF recommendations" which "helped the anti-USPSTF message rule the media all of last week."

Discussion Questions

1. As an exercise in futility, discuss with your sister, girl friend, wife, mother the USPSTF recommendations regarding breast cancer screening.

2. Do the same with your brother, boy friend, husband, father regarding the recommendations for prostate screening.

3. Why is there alleged a "public relations machinery" against the USPSTF?

Submitted by Paul Alper

Another medical blog

Robin Motz alerted us to the blog Medicine: Facts and Fictions, which is subtitled "Corrections to and explanations of medical stories in the news."

In particular, Robin noted an interesting post on meta-analysis.