Bell Curve

3 56 The National Conrextof women in different ethnic groups. The results for chilcircn ;I( least sixyears old and their mothers, shown in the tshle belc)w, indicate that thc.gap between the children is larger than the gap sepnrilting the mothers,Ethnic Differences in Test Scores in Two GenerationsGap Separating Gap SeparatingEthnic the Mothers the ChildrenComparison in IQ Points in IQ PointsWhite-black 13.2 17.5White-Latino 12.2 14.1by more than 4 points in thc case nt blacks and whites, by ;~lmost twupoints in the case of whites and Latinos. There :Ire technic:^! rcilsons 101461hcdgc on any inore specific interpretation of these di~r;~. We nlay ;~tleast- say that the results point in ;I worrisome direction.Pulling these differel~t views of thc situi~tion together, the d;lta revcbnldemographic pressures for further ethnic divcrgencc in IQ. Wc will nothazard a guess about the magnitude of ethnic divcrgencc or its spccd.Within another decade, assuming that the NLSY continues its testingprogram, guesses will not l7e necessary. When I;lrgc numhcrs of theNLSY women approach the end of their childbearing years and theirchildren have been tested after reaching an age when IQ scorcs arc st;~ble,we not only will he able to answer whether and how much ethnicgroups diverged for that generation of Americans but he ahle to pindown answcrs to many of the other qi~cstions about dysgenic effects niltionwide.IMMIGRATIONImmigration is an even older American trip wire for impassioned debatethan differential fertility, and the disputes continue to the presentday.4q The reason is not hard to find: America has more people flowinginto it than any other country. Aboilt half of the world's migrants resettlingin new countries are coming to Amcric;~ as we write.5" The pco.ple already living here have alwaysviewed this influx of newcomers withRegrcssion to the Mcan to the Rescue?Those who dismiss thc i~npclrtnncc of dysgcnic trcnds have ~nist;~ki~nlyI;~tched onto tl~c zc;~tistic;~l ph~~nomenun known as rcgrc,ssion to the mcan;IS a ~uagi cure-:dl. The cditorii~l pi~gc of the Nctcl York Titncs, no Icss, is onrecord with an assurance to its readers tllat hrcause of regression to themean, each successive generation of children of hclow-ilverage 1Q wonlcnwill get closer to IIX ;Ivcl-;lge and thcrcforc black ;~ncl whitc scorcs will tendto convcrgc.'" Alas, it clc>esn1t work th;~t wily. The results on the PI'VT provi~lc;\ concrele illustr~~tion.Suppow rrh;~t we rccalcul;~re rhc gap hetween t l i ~ a three ethnic groups in~wo sllccessive gcnerlrtions, this tiruc expressing thc~n in I orlns of standi~rd~lcviations based on the noth hers' ilnd childrcns' c)wn st;~nd;rrd devii~tions,IIC)I on thcir pl;~ce within tllc 1l;ltional J~stril>u~ion (as in the precedingt;~hle).Regression to the Mean and Ethnic Differencesin Test Scores in Two GenerationsEthnic Gap Separating Gap SeparatingComparison the Mothers the Childrenin SDsin SDsWh~tt-black 1.17 1.17Wh~tc-l.;~r~no 1.05 .93(lalcul;lted in this wily i~ncl shown in the rnhlc ;above, thc fi;~li hctwecn\vllilc% and 1,;ltino childre11 h;ls shrunk so~ncwhat cc>mparcti to thc gapscy>;lr;tti~~g tl~cir mothcrs. Thc g;\p bctwccn wl~it~ ;lnJ hlack childrrn hilsat le;~st grown no larger."& Why can wcx ohtitin this result and still show ;Igrowing gap in I(;! points between the ethnic grvups! The answer is that"me;lnV rcferre~l to in "regression to the mean" is thc ~x~pulution's own melz11.White childrcn ofdutl white wolncn will, on slaCragc, he closcr to the meanfor whites in their gc,t~er;~tion than thcir mothers wcrc in their gcnercation.A parnllcl st;lrement applies to hlack children of dull hlack women. Rutthis does not ncccss;~rily imply th;lt the IQ scores of hlack and whitc'children must hc closer to each other than thcir rrtothers' IQ scures were.It is a slippcry concept. Some pcvple find it is helpful to rcrrlemlics rharregression to the mcan works both ways: If you stilrr with population ofclull children and then find the IQs of their parcnts, you will find thatrhc parents were closcr to the mean (on ;\vc.ragc) than their children.Regression to the mcnn is ;I xti~tistic;~l phenomenon, not ;I hiologicitlone.