Gene Gallagher wrote:
> I have recently seen examples of the thrip fallacy in the op-ed
> pages of the Boston Globe. Massachusetts has implemented
> state-wide standardized testing and has increased state funding
> for school districts with low test scores. Statistical analysis
> reveals that Five or six socioeconomic factors
> (parents educational level, annual salary, % two-parent households,
> etc) account for over 90% of the variance in town-to-town K-12
> standardized test scores. The implication is that only 10% of
> the variance in mean test scores COULD be due to differences in
> curriculum, teacher quality, or financing for the school (Take
> that Teacher's Unions!). Some might conclude that spending
> money on schools & teachers since only 10% of the town-to-town
> variance in these scores could be due to factors outside the home.
> This fallacy fails to consider that a high median income and
> other socioeconomic factors often are strongly associated with
> a better tax base, lower class sizes, better trained teachers,
> more innovative curriculum etc.
> This fallacy should have a name, but I don't know it. I point
> my students to Wright's path analysis and structural
> modeling approaches (LISREL, and AMOS) to show alternatives
> to the misleading inference based on an R^2 in a multiple
> regression equation.
There is an additional fallacy here (I think). As I understand it they used
town-town means to infer a small effect of other factors on children's
education. This is an example of the ecological fallacy. The town mean scores
allow no firm inference about the effect of any factor on individual children
(they could be similar in magnitude, different in magnitude or even in
different directions).
Thom
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