STAT 221 Lecture 8 normal - Introduction Density curves...

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IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresChapter 3: The Standard Normal DistributionsSTAT/SOC/CSSS 221Patricia MartinkovaUniversity of WashingtonLecture 8: April 15, 20151/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresHousekeepingParticipation and Quiz 1 grades on CanvasAny disputes must be raised during this weekHomeworkHW 4 (Ch 3) will be due next TuesdayThursday Lab (April 16)Eric’s sections (AA/AB) in Thompson -bring laptops!No software needed besides web browserLet Eric know if you are not able to bring laptopGo to Savery 117Lanu’s sections (AC/AD) in Savery 121Andrew’s sections (AE/AF) in Savery 117There will be a lab assignment - due next Friday2/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresWarm up - Quiz 1How many scores are smaller than 10?How many scores are greater than 14 ?Is this distribution symmetric, skewed to the right or to the left?3/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresWarm up - Quiz 1What percent of scores are smaller than 10?What percent of scores are at or between 12 and 14 points?What percent of scores are at or between 11 and 15 points?4/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresWarm up - ACT scoresWhat percent of ACT Math scores are between 12 and 24?38%50%53%68%77%86%90%95%99%5/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresWarm up - ACT scoresWhat percent of ACT Math scores are between 6 and 30?38%50%53%68%77%86%90%95%99%6/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresExploring the data”First steps” when you get new data(on asingle quantitative variable)1.Plot your data - make a histogram (Ch 1)2.Look for the overall pattern (shape, center, spread)and for outliers (Ch 1)3.Describe the center and spread in numbers (Ch 2)Todaywe add one more strategy (Ch 3):4.Sometimes the overall pattern of a large number of observations is soregular that we candescribe it by a smooth curveThis smooth curve is called adensityThe smooth curve we will mostly discuss this week is aNormal curve7/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresDensity curves8/32
IntroductionDensity curvesNormal distributions68-95-99.7 ruleStandard scoresDensity curveAdensity curveis an idealized description of a distribution of dataAdensity curveis amodel of a distributionModel is like reality, but more simpleAll models are bad... but some areuseful9/32

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