Sta­tis­ti­cal think­ing

Finweek English Edition - - LETTERS -

THE LET­TER FROM F Coetzer (“Stan­dard de­vi­a­tions”, 3 De­cem­ber 2010) refers. Coetzer re­sponds to the ex­pla­na­tion of the ad­mis­sions pol­icy at the Uni­ver­sity of Cape Town (in a let­ter from Gerda Kruger, 4 Novem­ber) by at­tempt­ing to re­in­force colum­nist Stephen Mulholland’s pre­vi­ous as­ser­tion that by ad­mit­ting some stu­dents with lower ma­tric marks than oth­ers, the Uni­ver­sity of Cape Town (UTC) will pro­duce groups of “medi­ocre” stu­dents and “bril­liant” stu­dents. He ar­gues that, sta­tis­ti­cally – on the ba­sis that there are fewer stu­dents in the in­ter­val be­tween 91% and 100% (the in­ter­val for ac­cept­ing white ap­pli­cants) than be­tween 74% and 100% (the in­ter­val for ac­cept­ing black ap­pli­cants). On those grounds he ar­gues that be­cause there’s a nor­mal dis­tri­bu­tion of re­sults in both groups there must be more medi­ocre stu­dents in the black group ad­mit­ted to UCT.

He’s wrong. In fact, be­cause of the ex­treme ed­u­ca­tional dis­ad­van­tage faced by most black pupils their nor­mal dis­tri­bu­tion is sig­nif­i­cantly shifted to the left, such that there are in fact fewer black pupils scor­ing above 74% than there are white pupils scor­ing above 91%. That’s pre­cisely the root of the prob­lem – and the ev­i­dence of dis­ad­van­tage and the rea­son UCT ap­plies dif­fer­ent ad­mis­sions cut-offs.

We be­lieve tal­ent is ran­domly dis­trib­uted in all race groups, in all schools and ge­o­graph­i­cal ar­eas, whether ru­ral or ur­ban. We be­lieve the per­for­mance dis­tri­bu­tion within any school sys­tem or given set of en­vi­ron­men­tal de­ter­mi­nants is a con­se­quence of the dis­tri­bu­tion of tal­ent, plus mo­ti­va­tion, hard work and, no doubt, some op­por­tu­ni­ties. But, be­tween school sys­tems and en­vi­ron­men­tal set­tings, dif­fer­ent per­for­mances are much more in­flu­enced by those dif­fer­ing sys­tems. There­fore, to at­tract the bril­liant in all set­tings one should sim­ply se­lect the top 5% of stu­dents, re­gard­less of their ac­tual marks. That’s es­sen­tially what UCT’s sys­tem is do­ing. Not sur­pris­ingly, we find the top 5% from one school sys­tem will have marks that are much higher than the top 5% from a dif­fer­ent sys­tem.

Un­for­tu­nately, we also find the per­for­mance of the top 5% in some sys­tems is too poor; they just haven’t mas­tered enough dur­ing their 12 years of school­ing and the uni­ver­sity is un­able to make good that deficit, even though we recog­nise these ap­pli­cants have the raw abil­ity and mo­ti­va­tion to suc­ceed given the right sup­port. So we can’t ad­mit them.

But it’s just this sta­tis­ti­cal think­ing (as de­scribed by Coetzer) that re­sults in the ad­mis­sion of stu­dents from dif­fer­ent so­cio-eco­nomic com­mu­ni­ties and dif­fer­ent school sys­tems on the ba­sis of a dif­fer­ent set of marks. The proof we’re get­ting it right is that once they’re given the sup­port UCT can of­fer – in res­i­dence, with tu­tors and men­tors, and per­haps an ex­tra bridg­ing year of study – these stu­dents do as well as their peers with the high ma­tric marks.

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