11-21-08 - Psychology 206 Class Notes TYPE I ERROR Test...

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Psychology 206 – Class Notes – 11/21/08 TYPE I ERROR Test statistic z exceeds the critical value and we reject H0 But, H0 is (in reality) TRUE This is type I Error Researcher directly controls probability of Type I error with critical values Probability of Type I error is called alpha (alpha = .05 most common; alpha = .01, alpha= .001) We say: “The probability of Type I error is alpha=.05” Exercise #27 The null hypothesis is that the mean of the population of (birth) weights of infants born to mothers who smoke is greater than or equal to 2.81 kg. The mean of population of (birth) weights of infants born to mothers who smoke is significantly less than 2.81 kg. The null hypothesis is ALWAYS OPPOSITE OF THE ALTERNATIVE HYPOTHESIS. To be sure that your null hypothesis is correct, formulate your alternative hypothesis before you make your null hypothesis. LOOK FOR THE KEY TO EXERCISE #27- Monday Just make sure that you have enough room for your distributions, shade your rejection regions, check your null hypotheses, check your inequalities TYPE II ERROR Type II error is when you fail to reject the null hypothesis when it is really wrong
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