Is this result really counter intuitive?
Isn't the truly independent variable academic perceptions of the results.
If the exam board awards a high proportion of firsts, they may fear the credibility of their standards if the they also award high proportion of 2.1s. If they award a low proportion of firsts they may seek to assert the quality of their institution and the qualtiy of the teaching in that year by being more generous 2.1s. (This could be investigated by correlating the proportion of Firsts and 2.1s.)
Being surprised at the lack of correlation between Firsts and V betrays an assumption that exam scores are objective. But it is more realisic to view them as social products. An approriate method of investigation would be to have observers sitting in on Award Meetings and noting the way Exam Boards decide on the level of marks required for Firsts and 2.1s in the light of variation in exam questions and among markers.
Ray Thomas, Faculty of Social Sciences, Open University
-----Original Message-----
From: A UK-based worldwide e-mail broadcast system mailing list [mailto:[log in to unmask]] On Behalf Of kornbrot
Sent: 09 May 2008 10:31
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Subject: Correlation between non-independent variables
I am investigating UK university performance, & comparing 96 disciplines on proportion of students with highı performance. There are 4 categories: 1st, 2.1, 2.2, <2.2 I produce 2 measure for each of the 96 disciplines: Proportion achieving excellent degrees, i.e. 1st class, E; and proportion achieving very good degrees, i.e. 1st OR 2.1, V. One MIGHT expect that disciplines with high E, would also have high V. WRONG. There are 10 disciplines with E>=20 and 27 disciplines with V> 66.7. Medicine is the ONLY discipline which falls into the top 10 for E, AND the top 27 for V.
This is an interesting and counterintuitive finding that I would like to reinforce by giving the correlation between E and V. BUT E and V are clearly NOT independent Pearson r = .36, Kendallıs tau = .26, Spearmanıs rho = .38. I also have students incoming high school grades, UCAS points scores, U. Partial correlation E,V correcting for U = .023. It seems to me realistic to claim that excellent and v. good performance differences across disciplines depend differently on other factors. BUT still worried about non-independence of E and V PLEASE HELP with suggestions of better analyses It is the case that multiple regression of E and V on relevant factors give different results. BUT do not want to fall into fallacy of factor produces different effects on E and V, therefore V and E are different. If one does a multivariate regression with both E and V as response variables and looks for interaction, the non-independence of E and V is again a problem. HELP
Diana
Professor Diana Kornbrot
School of Psychology
University of Hertfordshire
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