Statistics 101 Class 8

Overview Hypothesis Testing Hypothesis Testing Stating the Research Question Stating the Research Question –Null Hypothesis –Alternative Hypothesis Type of Distribution Type of Distribution Determine cut off for rejecting the Null Determine cut off for rejecting the Null Example – SUPER BABY? Page 116 Example – SUPER BABY? Page 116 One and two tailed tests One and two tailed tests Type I and Type II Error Type I and Type II Error Research Example Research Example Homework Homework Summary Summary

Core Logic of Hypothesis Testing Considers the probability that the result of a study could have come about if the experimental procedure had no effect Considers the probability that the result of a study could have come about if the experimental procedure had no effect If this probability is low, scenario of no effect is rejected and the theory behind the experimental procedure is supported If this probability is low, scenario of no effect is rejected and the theory behind the experimental procedure is supported

The Hypothesis Testing Process 1. Restate the question as a research hypothesis and a null hypothesis about the populations  Population 1  Population 2  Research hypothesis  Null hypothesis

The Hypothesis Testing Process 2. Determine the characteristics of the comparison distribution  Comparison distribution

The Hypothesis Testing Process 3. Determine the cutoff sample score on the comparison distribution at which the null hypothesis should be rejected  Cutoff sample score  Conventional levels of significance: p <.05, p <.01

The Hypothesis Testing Process 4. Determine your sample’s score on the comparison distribution 5. Decide whether to reject the null hypothesis

Example Let’s do a careful walk through of the example on page 116 Let’s do a careful walk through of the example on page 116

One-Tailed and Two-Tailed Hypothesis Tests Directional hypotheses Directional hypotheses –One-tailed test Nondirectional hypotheses Nondirectional hypotheses –Two-tailed test

Determining Cutoff Points With Two-Tailed Tests Divide up the significance between the two tails Divide up the significance between the two tails

Decision Errors Type I error Type I error –Reject the null hypothesis when in fact it is true –alpha (α ) Probability of making a Type I error Probability of making a Type I error Type II error Type II error –Not rejecting the null hypothesis when in reality it is false –beta (β ) Probability of making a Type II error Probability of making a Type II error

Possible Correct and Incorrect Decisions in Hypothesis Testing

Hypothesis Tests in Research Articles Shown as asterisks in a table of results Shown as asterisks in a table of results

Homework P 142/3,4,5,7 P 142/3,4,5,7 P 145/17 P 145/17 P 183/13, 18 P 183/13, 18

Summary Hypothesis Testing Hypothesis Testing Stating the Research Question Stating the Research Question –Null Hypothesis –Alternative Hypothesis Type of Distribution Type of Distribution Determine cut off for rejecting the Null Determine cut off for rejecting the Null Example – SUPER BABY? Page 116 Example – SUPER BABY? Page 116 One and two tailed tests One and two tailed tests Type I and Type II Error Type I and Type II Error Research Example Research Example Homework Homework