edited 3/11/21

To skip PREFACE, use this  LINK to an earlier published version of this essay.

See, also, Part II: The Capacity to Benefit
from Formal Academic Schooling:
two ideologies of distribution.


Classification Error in Evaluation Practice:
the impact of the "false positive" on educational practice and policy
2008 Edward G. Rozycki

...we have not developed a formal way of reasoning probabilistically about this type of problem, ... clinical judgment may be faulty and ... current clinical practices may be inconsistent or incorrect. --  David M. Eddy, "Probabilistic reasoning in clinical medicine: Problems and opportunities" Chapter 18 pp. 249 - 267 in Daniel Kahneman, Paul Slovic & Amos Tversky (eds.) Judgment under uncertainty: Heuristics and biases. Cambridge University Press 1982. p. 267.

A Decision Simulation

Over several years of university classes I  would ask my students, mostly principals and superintendents in a doctoral program, whether they would consider using random testing to identify drug abuse in their schools. Here are the conditions for setting up the simulation:

1. the Drug Test (for brevity's sake, let us call it DT) would correctly identify 19 out of 20 "true" drug abusers;

2. Suppose that there are, at most, five percent of a total of 10,000 K-12 students abusing controlled substances;

3. the costs of the first use of DT for each student would be borne by the manufacturer; only reapplications of DT, if there were any, would have to be paid for at the rate of fifty dollars each.

4. To be minimally intrusive on the educational program, but maintain a hoped-for deterrent presence, only one or, at most, a few students would be selected each day by lottery to be tested by DT.

Over the years the considerations these experienced educators would entertain and the conclusions they would reach were pretty much the same: the great majority would say yes to implementing a program of random testing, despite much they found objectionable about it.

After this first stage of reaching a decision, I would caution them that DT would generate what are called "false positives," students mistakenly identified by DT as abusers, for whom such a determination might have severe social consequences. With reluctance the educators would insist they would implement the use of DT, but not push for criminal charges against these young people. Rather they would provide counseling and therapeutic support to the test-identified-users.

Politically sensitive, the principals and superintendents thought that drug abuse by the postulated 500 students would be perceived by important members of their communities to be so alarming that it would be worth the risk of identifying some students falsely as positive. As administrators used to tight budgets, they found the no-cost offer particularly enticing: a fifty-dollar per student saving.

  To continue, use his  LINK to an earlier published version of this essay.

Or see, also, Part II: The Capacity to Benefit
from Formal Academic Schooling:
two ideologies of distribution.