1 / 112

Practice

Practice. You wonder if psychology majors have higher IQs than sociology majors (  = .05) You give an IQ test to 4 psychology majors and 4 sociology majors. Psychology 110 150 140 135. Sociology 90 95 80 98. Results. Step 1: Hypotheses. Alternative hypothesis

edraj
Download Presentation

Practice

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. Practice • You wonder if psychology majors have higher IQs than sociology majors ( = .05) • You give an IQ test to 4 psychology majors and 4 sociology majors

  2. Psychology 110 150 140 135 Sociology 90 95 80 98 Results

  3. Step 1: Hypotheses • Alternative hypothesis • H1: psychology > sociology • Null hypothesis • H0: psychology = or < sociology

  4. Step 2: Calculate the Critical t • df = N1 + N2 - 2 • df = 4 + 4 - 2 = 6 •  = .05 • One-tailed • t critical = 1.943

  5. Step 3: Draw Critical Region tcrit = 1.943

  6. NowStep 4: Calculate t observed tobs = (X1 - X2) / Sx1 - x2

  7. X1= 535 X12= 72425 N1 = 4 X1 = 133.75 X2= 363 X22= 33129 N2 = 4 X2 = 90.75 9.38 = 363 535 72425 33129 4 4 4 (4 - 1)

  8. Step 4: Calculate t observed 4.58 = (133.75 - 90.75) / 9.38 Sx1 - x2 = 9.38 X1 = 133.75 X2 = 90.75

  9. Step 5: See if tobs falls in the critical region tcrit = 1.943 tobs = 4.58

  10. Step 6: Decision • If tobs falls in the critical region: • Reject H0, and accept H1 • If tobs does not fall in the critical region: • Fail to reject H0

  11. Step 7: Put answer into words • We Reject H0, and accept H1 • Psychology majors have significantly ( = .05) higher IQs than sociology majors.

  12. Practice • A research study was conducted to examine the differences between older and younger adults on perceived life satisfaction. A pilot study was conducted to examine this hypothesis. Ten older adults (over the age of 70) and ten younger adults (between 20 and 30) were give a life satisfaction test (known to have high reliability and validity). Scores on the measure range from 0 to 60 with high scores indicative of high life satisfaction; low scores indicative of low life satisfaction. Determine if age is related to life satisfaction.

  13. tobs = 4.257; t crit = 2.101 Age is related to life satisfaction.

  14. What if. . . . • The two samples have different sample sizes (n)

  15. Psychology 110 150 140 135 Sociology 90 95 80 98 Results

  16. Psychology 110 150 140 135 Sociology 90 95 80 Results

  17. If samples have unequal n • All the steps are the same! • Only difference is in calculating the Standard Error of a Difference

  18. Standard Error of a Difference When the N of both samples is equal If N1 = N2: Sx1 - x2 =

  19. Standard Error of a Difference When the N of both samples is not equal If N1 = N2: N1 + N2 - 2

  20. Psychology 110 150 140 135 Sociology 90 95 80 Results X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3

  21. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 N1 + N2 - 2

  22. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 N1 + N2 - 2

  23. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 23525 72425 N1 + N2 - 2

  24. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 23525 72425 3 4 4 3 4 + 3 - 2

  25. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 23525 23408.33 72425 71556.25 3 4 .25+.33 4 3 5

  26. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 23525 23408.33 72425 71556.25 197.08 (.58) 3 4 .25+.33 4 3 5

  27. X1= 535 X12= 72425 N1 = 4 X2= 265 X22= 23525 N2 = 3 265 535 23525 23408.33 72425 71556.25 114.31 3 4 .25+.33 4 3 5 = 10.69

  28. Practice • I think it is colder in Philadelphia than in Anaheim ( = .10). • To test this, I got temperatures from these two places on the Internet.

  29. Philadelphia 52 53 54 61 55 Anaheim 77 75 67 Results

  30. Hypotheses • Alternative hypothesis • H1: Philadelphia < Anaheim • Null hypothesis • H0:  Philadelphia = or >  Anaheim

  31. Step 2: Calculate the Critical t • df = N1 + N2 - 2 • df = 5 + 3 - 2 = 6 •  = .10 • One-tailed • t critical = - 1.44

  32. Step 3: Draw Critical Region tcrit = -1.44

  33. NowStep 4: Calculate t observed tobs = (X1 - X2) / Sx1 - x2

  34. X1= 275 X12= 15175 N1 = 5 X1 = 55 X2= 219 X22= 16043 N2 = 3 X2 = 73 219 275 16043 15987 15175 15125 3 5 .2 + .33 5 3 6 = 3.05

  35. Step 4: Calculate t observed -5.90 = (55 - 73) / 3.05 Sx1 - x2 = 3.05 X1 = 55 X2 = 73

  36. Step 5: See if tobs falls in the critical region tcrit = -1.44 tobs = -5.90

  37. Step 6: Decision • If tobs falls in the critical region: • Reject H0, and accept H1 • If tobs does not fall in the critical region: • Fail to reject H0

  38. Step 7: Put answer into words • We Reject H0, and accept H1 • Philadelphia is significantly ( = .10) colder than Anaheim.

  39. SPSS

  40. So far. . . . • We have been doing independent samples designs • The observations in one group were not linked to the observations in the other group

  41. Philadelphia 52 53 54 61 55 Anaheim 77 75 67 Example

  42. Matched Samples Design • This can happen with: • Natural pairs • Matched pairs • Repeated measures

  43. Natural Pairs The pairing of two subjects occurs naturally (e.g., twins)

  44. Matched Pairs When people are matched on some variable (e.g., age)

  45. Repeated Measures The same participant is in both conditions

More Related