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1、Chapter77.2(i)Thecoefficientofcigsinthefirstequationisnegative0.0044,whichmeansifsmokingonemorecigarette,thebirthweightofthebabywouldreduce0.44%,holdingthevariablesoffamincandparityfixed.IfDcigs =10then =-0.0044*10=-0.044=4.4%,whichmeansabouta4.4%lowerbirthweight.(ii)Holding
2、theotherfactorsinthefirstequationfixed,awhitechildpredicttoweighhigher5.5%(=0.055=5.5%)thananonwhitechild.What’smore,twhite=0.055/0.013»4.23,whichiswellaboveanycommonlyusedcriticalvalue.Thus,thedifferencebetweenwhiteandnonwhitebabiesisalsostatisticallysignificant.(iii)Thecoe
3、fficientofmotheducisaboutnegative0.003,whichmeansifmother’seducationyearsincreaseonemoreyear,thebirthweightofthebabywouldreduce0.3%,holdingtheotherfactorsinthesecondequationfixed.What’smore,tmotheduc=0.003/0.003=1,whichisbelowanycommonlyusedcriticalvalue.Thus,thedifferenceof
4、mother’seducationyearsisnotstatisticallysignificant.(iv)Fromthegiveninformation,I’munabletocomputetheFstatisticforjointsignificanceofmotheducandfatheduc,thereasonisthatthetworegressionsusedifferentsetsofobservations.Thesecondregressionusesfewerobservationsbecausemotheducorfa
5、theducaremissingforsomeobservations.IfwewanttocomputetheFstatistic,wewouldhavetoreestimatethefirstequationusingthesameobservationswhichisusedtoestimatethesecondequation.7.4(i)Thecoefficientofcalculusispositive4.41,whichmeansifastudenthaslearnedaboutbinaryvariableinthecalculu
6、s,thepercentagesofhisorhercourseinthetotalscoreswillincreaseby441%.Thisevaluationisnotreasonable.(ii)Whenwecontrolthevariableofmsugpa,theperformancesinhighschoolhelptopredictthescoresofMicroeconomicsTheory.(iii)Whenwecontrolothervariables,thedegreeofparentsdoesn’thelptopredi
7、ctthescoresofMicroeconomicsTheory.7.9(i)Fromtheequationy=β0+δ0*d+β1*z+δ1*d*z+u,weknowthatu=0andd=1,sowecangetf1(z)=β0+δ0+(β1+δ1)*z.(ii)Setf0(z*)=f1(z*),sowecangetβ0+β1*z*=β0+δ0+β1+δ1*z*,computeandgetδ1*z*+δ0=0,consideringδ1≠0,soz*=-δ0δ1.Onlywhenδ0δ1isnegative,z*ispositive,wh
8、ichmeansδ1andδ0musthaveoppositesigns.(iii)Usingpart(ii),becauseofδ0=-0.357a
