## July 8, 2004

### When you don't have all grades...

One more idea: what to do with districts that aren't unified—do not have students in all grades? There are bunches of districts in Texas and Massachusetts, for example, that have only elementary or only secondary grades. The iterative process for estimating student net flows relies on the whole grade span in two different ways—you need the upper grades to estimate the lower grades properly, and you need the lower grades to have a baseline net-migrant rate against which to compare the net-flow rates for high-school grades.

So the inverse (or converse) of a jackknife approach is called for.

The jackknife is a statistical procedure that allows one to capture how robust a summary measure is by selectively removing points and recalculating the measure without different points. If that set of jackknife measures clusters around the estimate for the whole sample (or population), then it's a fairly robust measure. (There are other uses for the jackknife, but that's beyond the point here.)

Here, we can use a jackknife-like procedure to get at the reverse—what is the measure for the deleted population? If we can find the net flows for a large area (like a state) and then the net flows for the state with an limited-gradespan district deleted, I think we can then find the net flows for the district. That takes care of the first problem. I'm still not sure how to get at the baseline net-migrant rate, though I suspect that in most places, a secondary-only district will have some elementary or unified districts clustering around it geographically, and one can probably use those figures as a reasonable baseline for the secondary district.

#### Reference

Efron, Bradley. 1982. Nonparametric estimates of standard error: The jackknife, the bootstrap and other methods. Biometrika 63: 589-599.

Listen to this articlePosted in Research on July 8, 2004 2:28 PM |