1 / 19

Outline

Stat 350 Lab Session GSI: Yizao Wang Section 016 Mon 2pm30-4pm MH 444-D Section 043 Wed 2pm30-4pm MH 444-B. Outline. Module 8, Two-Independent Samples t Test P-value Practice Midterm Feedback Please login with your UMID today. Two-Independent Samples t Test.

ksena
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Stat 350 Lab SessionGSI: Yizao WangSection 016 Mon 2pm30-4pm MH 444-DSection 043 Wed 2pm30-4pm MH 444-B

  2. Outline • Module 8, Two-Independent Samples t Test • P-value Practice • Midterm Feedback • Please login with your UMID today.

  3. Two-Independent Samples t Test • Used when comparing the means of two populations that are not related or matched in any way • Null hypothesis: μ1 – μ2 = 0 • Assumptions:(a) Eachsample is a random sample from each of the two populations.(b) Two random samples are independent of each other.(c) Eachpopulation is (approximately) a normal population.(d) For the pooled version we additionally assume that the populations have equalpopulation variance (standard deviation). • General and pooled versions have different test statistic formulas.

  4. Two-Independent Samples t Test Determining general vs. pooled (p 51) • Compare sample standard deviationssimilar s1 and s2 => pooled • Compare IQRs (by boxplots)similar lengths => pooled • Levene’s testp-value > α = 0.05 => pooled

  5. Module 8 Activity • Background: A total of 38 college freshmen were administered the Survey of Study Habits and Attitudes (SSHA), a psychological test designed to measure motivation and attitude towards study habits in college students, at a private college. The 38 students were a simple random sample, of which 18 were female and 20 were male. • Ctools SSHA.sav • Task: Perform a two-independent samples t-test to assess if there is a difference between the mean score for women on the test and the mean score for men on the test. • Page 50-54

  6. What is the specific parameter of interest? p μ μd μ1 – μ2 p1 – p2

  7. Select the appropriate alternative hypothesis Ha: μ ≠ 0 Ha: μd ≠ 0 Ha: μ1 – μ2 ≠ 0

  8. Select the appropriate assumptions for this test. Choose all that apply... • Random sample • Normal population • Independent samples

  9. Random sample. Normal population. Both samples (the observed 20 male and 18 female SSHA scores) are random. Both populations (all male and all female SSHA scores) follow a normal distribution. A and B are wrong! Why?

  10. How many QQ-plots are needed to check the normality assumption? 2 1 0 – you should use a sequence plot

  11. What is the value of the test statistic? • 2.032 • 2.056

  12. What is the distribution of the test statistics if Ho is true? • N(0,1) • N(μ,σ) • t(n-1) • t(min{n1-1, n2-1}) • t(n1+n2-2)

  13. What is the p-value? • 0.05 • 0.05/2 • 0.047 • 0.047/2

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

  15. Yes or No Based on the 95% confidence interval of (0.042, 39.569), would you reject Ho at the 5% level?

  16. Module 8 • Good summary on three t test scenarios p57One sample t testPaired t testTwo-independent samples t test • Exercise on t test scenarios p58

  17. P-Value Practice • State the p-value expressionp-value = P (t directionvalue) • Sketch the t-distribution and shadow the desired tail (tails) • Find the bounds of (interval including) p-value • Decision

  18. Midterm Feedback • Please finish the anonymous survey at the following link:http://www.surveymonkey.com/s.aspx?sm=z0UmqIhkg4NY92fmlZds6g_3d_3d • The link is emailed to your mailbox@umich. • Any comments on Yizao’s teaching will be warmly welcomed.

  19. Extra Credit Opportunity • Exam 2 is only 3 weeks away! • There will be another extra credit opportunity next week (March 17 to 21) • Two points added to your 2nd midterm score • Mark your calendars now - the link will be on Ctools soon. • Have you got your extra credit for first midterm? Check it on Ctools.

More Related