STATS 250 1st Edition Lecture 10 Outline of Last Lecture I HT Module 0 an Overview of Hypothesis Testing II HT Module 1 Testing Hypotheses About a Population Proportion III If n is Small Outline of Current Lecture I Sample Size Statistical Significance and Practical Importance Current Lecture I Sample Size Statistical Significance and Practical Importance a When there is a small to moderate effect in the population a small sample has little chance of providing statistically significant support for the alternative hypothesis b With a large sample even a small and unimportant effect in the population may lead to a conclusion of statistical significance c Statistically Significant only means that the data is strong enough to reject the null hypothesis d Warning 1 small samples make it very difficult to demonstrate much of anything e Warning 2 a huge sample size can make a practically unimportant difference statistically significant f Types of Errors i Type 1 error rejecting H0 when H0 is true ii Type 2 error failing to reject H0 when Ha is true 1 Probability of making a type 2 error 2 Probability of rejecting H0 when Ha is true 1 called the power of the test