Grand Canyon Institute Makes Vast Decisions Based on Half-Vast Data and Analysis

September 10, 2018

(Guest Post by Matthew Ladner)

The double-plus good propaganda generators are at it again here in the Cactus Patch- in the latest edition of the two-minute hate, the Grand Canyon Institute claims each private choice student is costing the state general fund more money than the public school students. In the instant-classic turn of phrase by Robert Pondiscio however, it is important not to make vast decisions based on half-vast data.

You can watch a public affairs show interview with the author here. In the author states that the analysis supports abolishing private choice programs. Just how half-vast is the Grand Canyon Institute analysis? Well they’ve basically done a two variable regression analysis with private school enrollment as the dependent variable, and they’ve hung their entire estimate on one of the two regression coefficients. The first problem, which sinks the entire analysis by itself, is that their dependent variable for Arizona private school attendance is unreliable.

GCI uses a federal source for private school attendance by state. That source however does not have anything like a 100% response rate (see the appendix) and lists 320 private schools in Arizona. If one however goes to the Arizona Department of Revenue report on private school tax credits, you find tax credit scholarship tax credits going to 362 different private schools. The list of 362 may or may not be exhaustive. So CGI has a flawed dependent variable on their hands- the reality is that we don’t know the number of students attending Arizona private schools- we don’t even know the number of schools.

Second off a regression analysis with two independent variables (% of students attending charters and private choice dollars, respectively) would likely a grade of incomplete¬†in an Introduction to Statistics class-if the instructor wanted to encourage the student and was feeling generous. The universe of other factors which influence private school attendance. A quick google search for instance revealed an analysis testing 14 separate variables– many of which were statistically significant. Arizona’s economy crashed during the period examined in the CGI analysis for instance, and the above analysis finds family income explains variance in private school attendance. Considering that the entire GCI analysis rests on a regression coefficient, failure to control for more than two variable would be deeply suspicious even if they had a valid dependent variable, which they don’t.

In short, the Grand Canyon Institute’s elephant went in search of a way to claim that Arizona’s private school choice programs were bad, and sure enough they (predictably) found it. The analysis reveals much more about CGI than private choice programs in the end.