Friday, November 5, 2010

Not quite grasping the placebo concept

Marcus A. Winters writing in the Manhattan Institute's City Journal says:
The charters’ random-selection policy has allowed Hoxby’s team to evaluate them with a randomized field trial (RFT), the kind of experiment often described by social scientists as the “gold standard” in research design. RFTs resemble the clinical trials performed by pharmaceutical companies, which test a new drug by assembling a pool of subjects, randomly assigning subjects to receive either the drug or a placebo, and then comparing the subjects’ condition. Similarly, Hoxby took a pool of subjects (students applying to New York City charter schools); took advantage of the random nature of the lotteries, which assigned the subjects either to charters or to traditional public schools; and then compared their academic achievement. Because access to a charter school is the only meaningful difference between the two groups—both applied to charter schools, after all—comparing the groups’ later achievement really will tell us what effect charters have on student performance.
I've seen researchers and commentators ignore potential issues with open-label studies (see here and here for background), but Mr. Winters is the first not only to mention placebos but to compare them explicitly to public schools. At the risk of beating a man while he's down, the use of placebos is based on the assumption that knowing that you are being treated can and often does produce a "meaningful difference between the two groups."

Caroline Hoxby never mentioned placebos in this paper and I'm certain she would never suggest that being randomly assigned a public school is equivalent to receiving a placebo in a double blind test.

Unfortunately Dr. Hoxby is not the one writing the articles.

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