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# Introduction to Hypothesis Testing.docx

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Queen's University

Psychology

PSYC 202

Ronald R Holden

Fall

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Introduction to Hypothesis TestingThe Logic of Hypothesis TestingHypothesis test a statistical method that uses sample data to evaluate a hypothesis about a populationSteps for a hypothesis test o State a hypothesis about a population o Set the criteria for a decision o Collect data and compute sample statistics o Make a decisionStep 1 State a hypothesis about a populationNull hypothesis H in the context of an experiment H predicts that the independent variable 00has no effect on the dependent variable for the population o There is no change no difference no relationshipnothing happened o The treatment has no effectAlternative hypothesis H in the context of an experiment H predicts that the independent 11variable does have an effect on the dependent variable for the population o There is a change a difference a relationship o The treatment does have an effectStep 2 Set the criteria for a decisionDetermine which values are likely to be obtained if H is true values close to the null 0hypothesisDetermine which values are unlikely to be obtained if H is true values very different from the 0null hypothesisTo find the boundaries that separate the high probability samples from the low probability samples we select an alpha levellevel of significanceAlpha levellevel of significance probability value that is used to identify the low probability samples used to define the concept of very unlikely in a hypothesis testCommonly used alpha levels are a005 5 a001 1 a0001 01Eg with a005 we separate the most unlikely 5 of the values the extreme values from the most likely 95 of the valuesSee Figure 84 on page 238Critical region composed of the extreme sample values that are very unlikely as defined by the alpha level to be obtained if the null hypothesis is true o If the sample data fall in the critical region the null hypothesis is rejected o Provide convincing evidence that the treatment does have an effect o Located in the extreme tails of the distributionTo find the boundaries for the critical region use the alpha level and the unit normal table o Eg for a005extreme 5 is split between two tails of the distribution so there is 25 or 0025 in each tail o Look up the proportion of 0025 in column C the tail of the unit normal table to locate a zscore of 196 o The extreme 5 is in the tails of the distribution beyond z196 and z196 o See page 2391

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