Sunday, September 12, 2010

Straight Line Projections

I call Bravo Sierra.

There are lots of ways to predict where things are headed and a straight line projection is probably used more often than it should be. However, in the absence of a compelling narative to the contrary, a straight line projection seems to make the most sense.

This brings us to Mesa Public Schools enrollment. For the fifth straight year enrollment has declined, this time by 2,400 students. If you look at the graph included with the news article, the enrollment decline looks like a straight line for the last three years, and it doesn't look very different four years ago.

For some reason, the district projected a decline of only 700 students this year, rather than the 2,400. On the surface, that seems like a mistake in estimating. Now the board has to deal with the unexpected decline in enrollment (and state funding).

What doesn't make sense to me is blaming the decline on SB1070 as the Superintendent has.

"We cannot underestimate the influence of political action and how it influences our community," Superintendent Cowan told the board. "Whether it's Senate Bill 1070 (the state's new illegal immigration law) or any other piece of legislation, as that goes into effect or is placed permanently on the shelf, it will have a real impact on our community."

Cowan estimated about two-thirds of the student loss this year may be associated with SB 1070, which was signed by Gov. Jan Brewer last spring. Much of the law has been put on hold by the courts, but advocates for immigrants said it spread enough fear among the Hispanic community that some families packed up and moved from the state.

If something external happened causing a larger than normal enrollment decline, one would expect to see a deviation from the trend of the last few years, not a straight line continuation of the trend.

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