Independent Sample t-Test and Mann Whitney U-Test

Read both excerpts from the two research articles and using the tables

Answer the following questions:

RESEARCH ARTICLE 1

Kristofferzon, M., Lofmark, R., & Carlsson, M. (2005). Perceived coping, social support, and quality of life 1 month after myocardial infarction: A comparison between Swedish women and men. Heart & Lung, 34(1), 39-50.

Introduction

Kristofferzon, Lofmark, and Carlsson (2005) conducted a comparative-descriptive study to deter¨mine if women and men differ in their perceived coping, social support, and quality of life one month post myocardial infarction (MI). The sample of convenience included 171 subjects, 74 women and 97 men. Each participant completed a study-specific questionnaire (demographics and risk factors), the JCS-60 (measured use of coping strategies), the social network and social sup¨port questionnaire (measured social participation and emotional support), the SF-36 Health Survey (measured perceived health-related quality of life), and the QLI (measured perceived quality of life). In addition, the researchers conducted a chart review of each participant’s medical record. In this study the results showed that “compared with men, women used more evasive and supportive coping and rated psychologic aspects of the heart disease as more problematic to manage. More women perceived available support from friends and grandchildren, and more men perceived avail¨able support from their partner. Women rated lower levels in physical and psychologic dimensions of quality of life” (Kristofferzon et al., 2005, p. 39).

Relevant Study Results

“A consecutive series of patients was selected from the medical records in 1 hospital between August 1999 and July 2001 for women and between August 1999 and August 2000 for men. With regard to a lower incidence rate of MI in women, a longer selection period was needed for them. . . , We decided to include 100 women and 100 men to have a comfortable margin for dropouts.

“An introductory letter, informed consent form, and questionnaires were mailed to eligible sub¨jects 1 month after an acute MI. After 1 week, the first author phoned the patients. Those inter-ested in participating returned the signed consent form and the completed questionnaires to the investigator within 1 to 2 weeks. The same questionnaires were mailed to the subjects on 3 occasions, 1, 4, and 12 months after ML Data from 1 month are presented in this article” (Kristofferzon et al., 2005, p. 41).

“Of the target population of 338 women, 20% died before inclusion, 35% did not meet the inclu¨sion criteria, and 23% declined participation; of the target population of 317 men, the correspond¨ing numbers were 17%, 27%, and 26%, respectively. . . . The final sample consisted of 74 women and 97 men” (Kristofferzon et al., 2005, p. 41).

In Table VI, are the quality of life measures reported by Kristofferzon et al. (2005) in their study of women and men following an MI. The level of significance or alpha for this study was set at 0.05.

TABLE VI ï Quality of Life Experienced by Women and Men (N = 171)

WOMEN (n = 74)

MEN (n = 97)

TVALUE

INSTRUMENTS AND COMPONENTS/SCALES

MEAN (SD)

(OF =169)

P VALUE

SF-36 (0 = low QoL, 1 00 = high QoL)

The Physical Component Score (PCS)*

48.5 (5.7)

51.1 (7.4)

-2.50

0.01

The Mental Component Score (MCS)f

48.2 (7.6)

51.4(7.5)

-2.74

0.007

Physical Functioning (PF)

51.3(23.7)

58.6(24.1)

-1.98

0.049

Role-Physical (RP)

4.7(14.1)

12.6(23.7)

-2.54*

0.007

Bodily Pain (BP)

57.6 (26.2)

62.5 (27.3)

0.24

General Health (GH)

51.1 (17.6)

54.2 (20.1)

0.30

Vitality (VT)

39.8(19.0)

47.5 (23.2)

-2.31 ß

0.02

Social Functioning (SF)

61.0(27.4)

66.1 (23.2)

0.19

Role-Emotional (RE)

27.5 (39.5)

37.8 (42.7)

0.11

Mental Health (MH)

62.3 (22.9)

72.7(20.1)

-3.15

0.002

QU (0 = low QoL, 30 = high QoL)

Totat Scale

20.1 (3.5)

21.2(3.6)

-2.06

0.04

Health Functioning

17.9(4.1)

19.3 (4.6)

-1.99

0.049

Socioeconomic

22.6 (3.6)

22.9 (3.7)

0.58

Psychologic/spiritual

19.6(4.6)

21.1 (4.3)

-2.10

0.04

Family (A/= 69 women and 94 men)

25.6 (4.7)

26.0 (3.9)

0.51

*PCS = PF, RP, BP, GH. WCS = VT, SF, RE, MH. *df = 161 .

W= 1 68. QoL- Quality of life;

QU, Quality-of-Life Index-Cardiac Version.

Kristofferzon, M., Lofmark, R., & Cartsson, M. (2005). Perceived coping, social support, and quality of life 1 month after myocardial infarction:

A comparison between Swedish women and men. Heart & Lung, 34(1), p. 47.

Study Questions:

1. t= -1.99 describes the difference between women and men post myocardial infarction (MI) for what variable?

2. Consider t = -2.74 and t = -2.31. Which calculated t ratio has the smaller p value? Provide a rationale for your answer.

3. Examine the results in Table VI. Which t ratio listed in the table had the largest p value? What was the focus of this t-test, and were the results significant? Provide a rationale for your answer.

4. What is df? Why is it important to know the df for a t ratio? How would you calculate the df for a t-test, and what is the df for this study?

5. What is the cause of an increased risk for Type I errors when t-tests are conducted? How might researchers eliminate the increased risk for a Type I error in a study?

6. Does this study meet the assumptions for the t-test? Provide a rationale for your answer.

7. What sampling method did the researchers use in this study? Provide a rationale for your answer.

8. What level of data is analyzed by means and standard deviations? Is this level of data compatible with the assumptions for the t-test? Provide a rationale for your answer.

9. Is the sample size adequate to detect significant differences between the two groups in this study?

RESEARCH ARTICLE 2

Source: Tsai, S. L. (2003). The effects of a research utilization in-service program on nurses. International Journal of Nursing Studies, 40(2), 105-13.

Introduction

Tsai (2003) conducted a quasi-experimental study to examine the impact of an 8-week research utilization course on nurses’ attitudes towards nursing research, their research participation, and utilization of research findings. Study participants were divided into an experimental group (n = 47) and a control group (n = 42); a pretest (Tl), posttest (T2), and a 6-month follow-up (T3) tests were administered. To evaluate the nurses’ attitudes towards research, a 29-item scale with a 5-point scoring system, where 5 meant total agreement and 1 meant total disagreement, was developed. Higher scores denoted more positive attitudes towards nursing research. The research¨ers used Mests to compare test scores of both groups. The experimental group displayed a more positive attitude towards research than the control group.

The Mann-Whitney U test was used to measure the differences in research participation between the experimental and the control groups over time. Subjects’ scores were calculated using a 33-item questionnaire with a 2-point scoring system, where 1 meant participation in a particular activity and 0 meant no participation. The alpha or the level of significance for this study was set at 0.05. “The results showed that there were significant differences in attitudes between the two groups toward research and perceived support of institutions. Participation in research also differed significantly when ana-lyzed at posttests 2 and 6 months after the course. There was no significant difference in research uti-lization. These results suggest that continuous consultation and assistance should be provided to the nurses after the course, so as to implement the results of research utilization” (Tsai, 2003, p. 105).

Relevant Study Results

“The degree of research participation was compared between the two groups by the Mann-Whitney U test. There were no significant differences between the two groups in the pretest comparison (z = -0.7, p > 0.05)” (Tsai, 2003, p. 109). However, the differences were significant at T2 (z = -3.75, p < 0.05) and at T3 (z = -2.96, p < 0.05) after the research utilization courses. Nurses in the experi¨mental group had a higher degree of research participation [during the study than those in the control group] (Table 3).

^TABLE 3 ï Research Participation Over Time (N=89)

MANN-WHITNEY U

Variables

Median (0-33) z

Pretest

-0.07

0.944

Control

5.80

Experimental

6.00

-3.75

0.000

Control

4.00

Experimental

8.00

-2.96

0.003

Control

4.50

Experimental

9.00

Note: T2óat the completion of the course; T3ó6 month after completion of the course.

Tsai, S. L (2003). The effects of a research utilization in-service program on nurses. International Journal of Nursing Studies, 40(2),

Study Questions:

1. One of the research hypotheses from this study was: “Nurses who attend the research utilization course have higher score of participation in nursing research than those who do not” (Tsai, 2003, p. 106). State the null hypothesis.

2. What does “(0-33)” after the word “median” represent?

3. Mann-Whitney U is the appropriate statistical test to use in which of the following situations:

a. Interval/ratio level data with a skewed distribution of scores for study variables

b. The difference between two dependent groups is being examined.

c. The data are collected at the nominal level

d. Correlation or relationship between two groups is being examined

4. Why were the medians versus the means selected as the measure of central tendency fgor describing the variables in this study?

5. Was there a statistically significant difference between the control group and the experimental groups at the 6 month follow up test (T3)? Provide a rationale for your answer.

6. The researchers analyzed the nursesí attitude data as though it were at what level of measurement?

a. Nominal

b. Ordinal

c. Interval/Ratio

d. Abstract

7. If the researchers decided to compare nursesí attitude posttest scores (T2) of the experimental group to its 6 month follow up (T3) scores, what test would they have used? Provide a rationale for your answer.

a. Man-Whitney U test

b. T-test for independent samples

c. Chi-Squared (X2)

d. T test for dependent samples

8. Compare the median values of the experimental and the control groups over time. What trends do you note in the research participation in both of these groups? How might this affect the significant differences between these two groups?

Kellar, S.P. & Kelvin, E. (2013). Munros statistical methods for health care research (6thed.). Philadelphia, PA: Wolters Kluwer/Lippincott Williams & Wilkins. ISBN: 13: 978-1-4511-8794-6

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