Gene Gallagher wrote: > [snip] > 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. [snip] I think that this is just a multiple-correlation version of the old adage that "correlation doesn't imply causation". If we think about it logically, the fact that parents have a great deal of money in their bank account can't possibly affect students' learning in any direct sense. It can operate only though such causal mechanisms as better opportunities to learn at home, better facilities at home to support learning, better psychological environment to support student motivation (maybe?), together with the school-based variables you identify in the above paragraph. Another name for the phenomenon would be that parental income is a proxy variable for the variables that affect learning directly. > One could experimentally demonstrate this fallacy by > transferring students from affluent communities to communities whose > schools have dismal standardized test scores. Somehow, I don't > think the parents would accept the statistical argument that the > their children's mean scores could decline at most 10% since 90% of > the variance was due to socio-economic variables. I accept the premise of such a hypothetical study -- unlikely to ever be realised, as you recognise -- but I'd point out that you are making an unwarranted slide in argument from "10% of the variance" to "10% of the mean scores". Mean scores and variance estimates are not related in this way. Paul Gardner
begin:vcard n:Gardner;Dr Paul tel;cell:0412 275 623 tel;fax:Int + 61 3 9905 2779 (Faculty office) tel;home:Int + 61 3 9578 4724 tel;work:Int + 61 3 9905 2854 x-mozilla-html:FALSE adr:;;;;;; version:2.1 email;internet:[EMAIL PROTECTED] x-mozilla-cpt:;-29488 fn:Dr Paul Gardner, Reader in Education and Director, Research Degrees, Faculty of Education, Monash University, Vic. Australia 3800 end:vcard
