stores in high promotion condition have higher average sales than stores in other conditionsReason: rejecting the null simply means that at least the average for one group is different from others, but didn’t say which group43
15Tests of Differences1. One Sample2. Two IndependentSamples3. PairedSamples4. More ThanTwo SamplesWhich test to use? It depends on (1). the number of variables and (2). Number of groups involvedt testsANOVA44•One-Sample t-test–One sample•Independent Samples t-test–Two independent samples•Paired samples t-test–Two dependent samples•ANOVA–Two or more samplesSummaryAverage temperature inAugust = 17°Sales in store A = Sales instore BKnowledge of statisticsafter class = before classAverage fuel prices insuburbs A,B and C aredifferent45Side topic - some further clarification of the distinction between relational and comparative RQs46
1647So far we have suggested that there is a close correspondence between the type of RQ and statistical tests usedHypothesisTestingTest of Association(relational RQ)Test of Differences(comparative RQ)MeansProportionsDifferent forms of t test/ANOVA•Cross tabulation•Correlation•Multiple regression48It is important to recognize that the distinction is artificial and sometimes not so clear-cutExamples of a relational RQ1.Does genderaffect how frequently people eat fast-food?2.Does education attainmentaffect how frequently people eat fast-food? 1.Do men and women differ in how frequently they eat fast-food?2.Does the frequency of fast-food consumption differ across people of different levels of education?11149What characterizes these types of RQ is that the independent variable (IV) is a categorical variable while the dependent variable (DV) is metricExampleDoes education attainmentaffect how frequently people eat fast-food?•There is no test of association for this type of RQ (for test of associations both variables need to be categorical or metric, but not one of each type)•What you need to do is to first re-phrasethe relational RQ as the corresponding comparative RQ and then choose the corresponding test of differences (an independent-samples t test or one-way ANOVA)IV iscategoricalDV is metric
17Today’s agenda50•Hypothesis testing – tests of differences–Different types of t tests–Two-tailed vs. one-tailed test – ANOVA•How to write about hypothesis testing•A few words on assignment 2How to write about hypothesis testing – the formulaic approach• 1ststep – describe the test– Which test did you use?– What variables are involved?–What are the groups involved?