diagnosing spina bifida诊断脊柱裂的问题课件

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1、Problem:DiagnosingSpinaBifidaTheprocedureofamniocentesisinvolvesdrawingasampleoftheamnioticfluidthatsurroundsanunbornchildinitsmother’swomb.Highconcentrationofalphafetoproteincanindicatetheconditionspinabifida.Concentrationofalphafetoproteintendstoincreasewiththesizeofthefoetus.Amn

2、iocentesisresultsinmiscarriagefor1%.Preliminarytestsinvolvemeasuringthelevelofalphafetoproteininthemother’surine.Problem:DiagnosingSpinaBifidaFormotherswithnormalfoetuses,themeanlevelofalphafetoproteinis15.73moles/litrewithastandarddeviationof0.72moles/litre.Formotherscarryingfoe

3、tuseswithspinabifida,themeanis23.05andthestandarddeviationis4.08.InbothgroupsthedistributionofalphafetoproteinappearstobeapproximatelyNormallydistributed.23.0515.73Problem:DiagnosingSpinaBifidaTooperateadiagnostictestforspinabifida,setathresholdconcentrationofalphafetoprotein,T,say

4、.IfthealphafetoproteinlevelisbelowT,thenthefoetusisdiagnosedasnothavingspinabifida.IfthelevelisaboveT,thenfurthertestingisrequired.Problem:DiagnosingSpinaBifidaIfTwassetat17.80moles/litre:Whatistheprobabilitythatafoetuswithspinabifidaiscorrectlydiagnosed?Whatistheprobabilitythataf

5、oetusnotsufferingfromspinabifidaiscorrectlydiagnosed?Iftheywantedtoensurethat99%offoetuseswithspinabifidawerecorrectlydiagnosed,atwhatlevelshouldtheysetT?WhataretheimplicationsofsettingTatthislevel?Chapter6ContinuousRandomVariablesIfarandomvariable,X,cantakeanyvalueinsomeintervalo

6、fthereallineitiscalledacontinuousrandomvariable.EgHglevels,height,weight,alphafetoproteinconcentration,cellradius,etc.(i.e.usually‘measures’)§6.1pages231-233TheStandardizedHistogramExample:DietaryCarbohydrateintheWorkforceTheaveragedailyintakeofcarbohydrateinthedietof5929people.20

7、0400600800Carbohydrate(g/day)0.002.000.004TheStandardizedHistogramThehistogramofthedatashowsthecarbohydrateintake:Isunimodal(modalclass200–225g/day)200400600800Carbohydrate(g/day)0.002.000.004TheStandardizedHistogramThehistogramofthedatashowsthecarbohydrateintake:Skewedtolargervalu

8、es(skewedright)20040060080