Lab 7 Worksheet Indep & Related t 2

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Name:___ Tasnia Ahmed ______________ Lab #7: Independent- & Paired-Samples t -Tests PSYCH 248 PLEASE TYPE ALL ANSWERS IN BLUE . ROUND ALL ANSWERS TO TWO DECIMAL PLACES (i.e., 0.05). Part A Compare 2 groups: Do pet owners differ from those with no pets in the number of annual therapy visits? Test it using the data below on the number of visits to a therapist over a year. Copy or enter the data into excel, save the file as csv and open it in JASP. Pet owners : 1, 3, 4, 5, 2, 4, 6, 8, 3, 4, 1, 2, 9, 1, 4, 2 No pets : 2, 4, 5, 6, 1, 7, 8, 9, 14, 5, 3, 2, 4, 8 1. Is this a between-subjects or within-subjects design? Between-subjects design 2. What is the independent variable? Whether parbcipants have pets or not 3. What is the dependent variable? Number of therapy visits over a year 4. Is the hypothesis one-tailed or two-tailed? Two-tailed 5. State the null hypothesis in words. There is no significant difference in the number of visits made between those who have pets and those who do not have pets. 6. State the null hypothesis in symbols. H 0 : μ d = 0 7. State the alterna7ve hypothesis in words. There is a significant difference in the number of visits made between those who have pets and those who do not have pets. 8. State the alterna7ve hypothesis in symbols. H A : μ d ≠ 0 In JASP, click T-Tests > Classical > Independent Samples T-Test . Transfer Visits to the Variables box and Owner to the Grouping Variable box. Run Student t, specifying your Alt Hyp. Under Assumpbons check Normality ,3 Equality of Variances (Levene) , Addibonal Stats: Loca>on Parameter ( Confidence interval 95%) , Effect Size ( Cohen’s d) , Descrip>ves , and Descrip>ves Plots . 9. According to the Shapiro-Wilk test of normality and Levene’s test of equality of variances, is it appropriate to use Student’s t -test to analyze these data? How do you know? It is appropriate as the result shows p is greater than 0.05. 10. What is the sample size (n)? 30 11. What is the mean number of visits for pet owners? 3.688 12. What is the mean number of visits for non-owners? 5.571 13. What is the standard devia7on for pet owners? ___ 2.387 ___________ 14. What is the standard devia7on for non-owners? ___ 3.458 ___________ 15. Descrip>ves plots creates a graph with the mean and 95% confidence interval for the mean for each group. What is the approximate percentage of overlap between the two intervals? 50% 16. What is the value of t ? -1.755 17. What are the degrees of freedom? 28 18. What is the significance value? 0.090 19. What is the 95% confidence interval? -4.083 - 0.315 20. What is the value of Cohen’s d ? -0.642 1

21. Report the results of this test in APA format. We fail to reject the null hypothesis as there is no significant difference in the number of visits made between those who have pets (M = 3.688, SD = 2.387) and those who do not have pets (M = 5.571, SD = 3.458), with t(28) = -1.755, p = 0.09. 2

Part B Test Change over 7me: Your hearing threshold is the minimum sound level you can detect. This study tested the hypothesis that the hearing threshold is more sensi>ve or beLer (i.e., lower numbers) aker an hour in a sensory deprivabon chamber compared to before. Eight parbcipants had their hearing checked both before and aker they were in a dark, silent chamber for an hour. Copy or enter the data into excel, save the file, and open it in JASP. Before: 11, 34, 18, 33, 35, 22, 35, 25 A@er: 13, 31, 18, 29, 32, 20, 28, 25 22. Is this a between-subjects or within-subjects design? Within-subjects design 23. What is the independent variable? The hours spent in the sensory deprivabon chamber. 24. What is the dependent variable? Hearing in terms of how much or well they can hear. 25. Is the hypothesis one-tailed or two-tailed? One-tailed 26. State the null hypothesis in words. The hearing threshold stayed the same or increased aker spending bme in the sensory deprivabon chamber. 27. State the null hypothesis in symbols. H 0 : μ d ≥ 0 28. State the alternabve hypothesis in words. The hearing threshold stayed the decreased aker spending bme in the sensory deprivabon chamber. 29. State the alternabve hypothesis in symbols. H A : μ d < 0 In JASP, click T-Tests > Classical > Paired Samples T-Test . Transfer ANer and Before (in that order) to the Variable pairs box. Under Alt Hypothesis , indicate the correct alternabve hypothesis. Check off Normality , Loca>on parameter (no confidence interval), Effect Size , Descrip>ves , and Descrip>ves Plots . 30. According to the Shapiro-Wilk test of normality, is it appropriate to apply parametric tests to analyze these data? How do you know?__ It is not appropriate as results show p is less than 0.05. ___ 31. What is the sample size (n)? __ 8 ___ 32. What is the mean hearing threshold before the sensory deprivabon chamber? 26.625 33. What is the mean hearing threshold a@er the sensory deprivabon chamber? 24.500 34. What is the standard devia7on before the sensory deprivabon chamber? 9.086 35. What is the standard devia7on a@er the sensory deprivabon chamber? 6.824 36. What is the approximate percentage of overlap between the two 95% confidence intervals? 40% 37. What is the value of t ? -2.147 38. What are the degrees of freedom? 7 39. What is the significance value? 0.034 40. What is the mean difference? -2.125 41. What is the value of Cohen’s d ? - 0.759 42. Report the results of this test in APA format. ___ The results on the test indicated a significant increase in sensibvity aker being in a sensory deprivabon chamber (M=24.5, SD=6.824) compared to before the sensory deprivabon chamber (M=26.625, SD= 9.086), with t(8) = -2.147, p= 0.034. 3

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Cohen’s d found a large effect size of d = -0.759. 43. How do the results differ if we transfer Before into the Variable pairs box first, followed by ANer ? The t value changes signs and significance level changes so that it is no longer significant if we were to change the order of the variables transferred from Aker then Before to Before then Aker. 44. Can we reject the null hypothesis if we ran this analysis as a two-tailed test? Why or why not? No, because it would need to no longer be in the cribcal zone as in it has to be below 0.025. 4

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