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Lecture 5

Crim 320.Week 5 February 5.docx

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CRIM 320
Rebecca Carleton

Crim 320 February 5 2013 Chi square analysis and measures of associationObjectivesoutline the steps involved in conducting a chisquare analysis conduct and interpret a chisquare analysisexplain and interpret lambdaexplain and interpret gammaknow when to use each of the testschi square uses a nominal variablenames labels exhaustive and exclusive categoriesthere are no mathematical qualities to nominal variables ex male femalea nominal level variable could never be considered normal it will never take on a normal curveThe basic idea and logic of chi square analysisare two variables related to one anothernull hypothesis the two variables are independentmust understand 2 related concepts 1 expected countswhat would occur if no relationship 2 observed countswhat we actually seeif the observed counts are sufficiently different from the expected counts we reject the null hypothesisall we can tell from a chi sq analysis is whether or not two variables are related to one anotherthe associationif the hypothesis is null the variables are independent and there is no relationshipwe can make this claim premised on the idea of the difference between what wed expect to happen if the variables were not related and what we actually see happen in the datasetif there was no relationship the numbers assigned to each category would expected to be randomarbitrarythe difference between expected and observed is the chi square value Online readingdoes showing up at a domestic violence assessment vary depending on who reported the crimetwo nominal variables 1 dichotomousyesno did he or she show up for assessment 2 categoricalno domestic violence father reported mother reported both reported research question is there a relationship between who reported domestic violence and whether somebody showed up for a domestic violence assessmentnull hypothesis there is no such relationship as with all chi square analysisSteps for chi square 1 calculate expected values 3 steps 2 observedexpected2expected 3 sum across all cells 4 calculate degrees of freedom 5 determine if we can reject the null hypothesisTable 2 Reported Domestic Violence and Showed Up for AssessmentDV SubcategoryNo DV Father Mother Both Reported Reported Reported No YesStep 1 Column and row marginals 70710087 Table 21 Reported Domestic Violence and Showed Up for AssessmentDV Subcategory No DV Father Mother Both Reported Row Marginals Reported Reported No 70 7 10 0 87
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