Choosing Significance Level Section 10.3

Starter At the local bakery, loaves of bread are supposed to weigh 1 pound, with standard deviation 0.13 pounds. You believe that today’s loaves are too heavy. You want to test this idea at the α =.05 level. You weigh 20 loaves and find a mean weight of 1.05 pounds. 1.State your null and alternative hypotheses. 2.Find the test statistic (z) and the p-value for your test by two different methods. 3.State your conclusion clearly in a complete sentence.

Today’s Objectives Students should be able to discuss issues involved with selecting the α level of a test Students should be able to state shortcomings of P-level as sole criterion –How do outliers affect P? –Why might a confidence interval be more useful than a hypothesis test? California Standard 18.0 Students determine the P- value for a statistic for a simple random sample from a normal distribution.

Choose an appropriate level of significance (alpha) How will the conclusion be used? How plausible is H o What are the consequences of rejecting H o ?

Assume SATM scores are N(475,100). 100 students take a prep course that claims to improve scores. State the null and alternative hypotheses. If the students mean score is 491.4, is the result significant at the 5% level? –Use the calculator Z-Test screen. If the mean is 491.5, is the result significant at the 5% level? Conclusion: There is nothing “magic” about 5%; don’t act as if it were!

There is more to statistical significance than P-value! Plot your data –Look for outliers –Is the effect you seek visible in the data? Use a confidence interval –Estimates the size of an effect, not just presence or absence of the effect

Today’s Objectives Students should be able to discuss issues involved with selecting the α level of a test Students should be able to state shortcomings of P-level as sole criterion –How do outliers affect P? –Why might a confidence interval be more useful than a hypothesis test? California Standard 18.0 Students determine the P- value for a statistic for a simple random sample from a normal distribution.

Homework Read pages Do problems 61-65