Stat 350 Lab Session GSI: Yizao Wang Section 016 Mon 2pm30-4pm MH 444-D Section 043 Wed 2pm30-4pm MH 444-B

Today’s Agenda 5 Steps for Hypothesis Testing Review Module 6 Activity 1 One Sampe Test Procedures Module 7 Activity 1 Paired t Procedures In-Lab Review: confidence intervals Today’s Qwizdom is no longer anonymous. Please use your UMID to log in.

1. Set up the null and alternative hypotheses Hypothesis is about the population parameters (p, μ) H 0 represents statement of no effect H a represents what the experimenter would like to support Equal sign always goes to the H 0 The direction in H a is very important in calculating p-value The significant level is also set at this step (most of the time by the problem) 5 Steps for Hypothesis Testing

2.Check assumptions for performing the test and calculate the test statistic For 1-sample testing of population proportion, check (1) random sample (2) If np 0 >=10 and n(1-p 0 )>=10 Help the computation of p-value. What to do when (2) does not hold? (very rare case) For 1-sample testing of population mean, check (1) random sample (2) Normality of population Not crucial when n>=30, because of CLT 5 Steps for Hypothesis Testing

2.Check assumptions for performing the test and calculate the test statistic How to check random sample? Information from the problem Time plot if data is collected in time How to check normality? QQ plot Which statistic to use? Under normality assumption use z-statistic when σ is known (population proportion) use t-statistic when σ is unknown (population mean for most of the time) 5 Steps for Hypothesis Testing

3. Assuming H 0 is true, find the p-value p-value is, assuming H 0 is true, the probability of getting the same or more extreme test statistic in the direction of H a. It’s a conditional probability. p-value = P (t.s. type direction t.s. value) e.g. p-value = P (t <= -2) Test statistic type is decided according to the problem Test statistic value is then calculated Direction is equal and the direction in H a 5 Steps for Hypothesis Testing

4. Determine if the result is statistically significant p-value <= significance level: Reject H 0 (the test is statistically significant) p-value > significance level: Fail to reject H 0 5. Report a conclusion in the context of the problem There is sufficient evidence to say… H a There is no sufficient evidence to say… H a. 5 Steps for Hypothesis Testing

1.Set up the null and alternative hypotheses 2.Check assumptions for performing the test and calculate the test statistic 3.Assuming H 0 is true, find the p-value 4.Determine if the result is statistically significant 5.Report a conclusion in the context of the problem

Module 6 Activity 1 One sample t test procedures Ctools salmonella.sav We will start step by step with Qwizdom questions…

Order the steps for conducting a hypothesis test... 1)Assumptions and test statistic 2)State the hypotheses 3)Find the p-value 4)Conclusion 5)Decision

What is the response? A)Individual salmonella levels B)Average salmonella level

What type of variable is the response? A)Discrete B)Continuous

What type of parameter would be useful for summarizing this variable? A)Proportion B)Mean

What is the specific parameter of interest? p μ μ d μ 1 – μ 2 p 1 – p 2

Select the appropriate alternative hypothesis Ha: μ > 0.3 Ha: μ ≥ 0.3 Ha: μ < 0.3 Ha: μ ≤ 0.3 Ha: μ ≠ 0.3

What graph could be used to check the random sample assumption? Histogram Boxplot Time-series plot QQ-plot

What graph would be used to check the normal distribution assumption? Histogram Boxplot Time-series plot QQ-plot

What is the distribution of the test statistics if Ho is true? N(0,1) N(μ,σ) t(n) t(n-1)

Yes or No Are the results statistically significant at the 5% level?

Interpretations Test statistic: the observed sample mean was average distances (i.e standard errors) above the hypothesized mean of 0.3. P-value: the p-value of (0.059/2) = indicates that if the mean level is really 0.3 MPH/g, and if repeated random samples of the same size were drawn from the population of Salmonella enteritidis levels, the probability of observing a test statistic value as large as or larger is only

Paired t Procedures Similar to one sample t procedures (Module 6 Activity 1) μ D taking place of μ Paired difference vs. Difference of parameter of two populations (μ D vs. μ 1 - μ 2 )

Paired vs. Independent Difference Problem: are the books from Amazon.com cheaper than those from Borders? Scenario 1: pick 100 books randomly, record the price differences of two sellers and analyze. Scenario 2: pick 100 books randomly from Amazon.com and 100 books randomly from Borders, calculate the mean price of each group and calculate the difference and analyze. Which scenario is better for this problem?

Module 7 Activity 1 Ctools books.sav

Interpretation of p-Value If the null hypothesis is true and this procedure (experiment) was repeated many times, we would expect to see a T- test statistic value of or larger in 86.15% of the repetitions. Thus our data are not at all unusual under the null hypothesis theory.

In-Lab Review minutes Ctools\Lab info\in lab review on CI

Before We Finish … Questions and comments?