Each report compares
public and private school sectors for a single year. Yet measuring
effectiveness requires at least two years of data, since different
schools start from different places. This shortcoming is compounded by
selection bias: Different populations with different test scores choose
to attend different schools. When schools have different scores, is it
the type of school that makes the difference or is it the students who
attend? In Wisconsin, as in many other states, private or charter
schools sometimes even have admission requirements, which means some
schools have test score advantages before they get out of the gate.
The WILL researchers
attempt to resolve this selection bias problem by considering
(controlling for) outside factors in their analyses. This is the basis
for the “apples to apples” claim. Unfortunately, this consideration is
limited to five apples out of a decent-sized barrel: (1) school-based
enrollment counts, (2) race, (3) ELL status, (4) economically
disadvantaged and (5) grade levels served by the school (p. 5). The
analyses do not include prior test scores of individuals or even
schools. That is insufficient for claiming one sector is performing
better or worse than another.
Our reviewer noted
substantial missing data for private schools — which the WILL report
acknowledges, yet still insists it is producing “something approximating
an ‘apples-to-apples’ comparison.” Then, the school is rated on the
aggregated percent proficiency for schools, rather than a full continuum
of test scores. This is arbitrary and different grades and subject
matters have different cut scores. An improvement from last year is the
use of the now commonly required ACT test, but how this is used is
unclear.
Perhaps the most unusual
research method they applied involves the calculation of disability
rates. Not trusting the state’s reported rates, they used estimates from
an earlier University of Arkansas study on Milwaukee. This assumes the
whole state has the same disability rates as the city. But that’s not
all. The earlier study was based on an estimated range rather than a
count. Referring to the high end of this estimated distribution, “I assume (emphasis
added) the disability rate is a factor of 8.125.” (p. 14). That is,
they eyeballed the data, plucked a number and used it as the basis of
their statistical analysis. Strange things happen when you pick a number
— such as one school having “a disability rate exceed(ing) 100%” of
their enrollment. The report acknowledges that these assumptions are
“very rough.”
Most of these shortcomings
were explained in last year’s expert review by Professor Ben Shear, and
they were thus available to the WILL researcher, yet they were repeated
in the latest report. The result is not apples-to-apples, it is
applesauce.
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