Assignment 3
NAME:
Your goal is to get more familiar performing t-Tests in Jamovi. This assignment is due at 8:00AM on Thursday, April 7th, uploaded to Courses. There are two data sets this time, one for the independent tests and one for the related tests. Make sure you are using the correct dataset for the corresponding questions.
Independent Samples t-Tests
The data for this assignment come from a study of an online chronic pain management program. A total of 275 individuals with chronic pain were randomly assigned to either a treatment (n = 133) or a control condition (n = 142). At the start of the study, researchers collected a number of background variables (e.g., age, frequency of exercise, gender), and a 7-point depression scale. Individuals in the treatment group participated in the online pain management program for approximately 6 weeks, whereas individuals in the control group received no treatment during the six-week period. At the end of the intervention period, researchers administered a 6-item scale measuring pain interference with daily life (dependent variables). The table below provides detailed information about the variables in the data set.
Variable Name
Definition
Response Scale
FEMALE
Respondent gender (0 = male, 1 = female)
0-1
AGE
Respondent age
TXGROUP
Treatment condition (0 = control, 1 = treatment group)
0-1
EXERCISE
Frequency of exercise
1-20
DEPRESS
Scale score computed by averaging seven questionnaire items
1-4
INTERFERE
Scale score computed by averaging six questionnaire items
1-8
The goal of the analysis is to determine whether the treatment and control groups differed on the INTERFERE scale score at the end of the study (i.e., Does the treatment change one’s level of pain interference with daily life). Perform a two-tailed independent t-test and answer the following questions.
What is the null hypothesis for the analysis?
By how much did the treatment group means differ on the pain interference scale?
Which value of the printout tells you the expected size of the mean difference between two groups of participants drawn from a population with equal groups (i.e., the mean difference due to sampling error or “random chance”).
What is the t-statistic for this analysis? How would you interpret that value?
The two-tailed probability value for the t-test prints is < .001 (less than 1 in 1000, or less than one-tenth of one percent, .10%). How would you interpret that value? Based on the probability value, what is true regarding the null hypothesis? Based on your response to the previous question, which of the following interpretations is correct? There is a reliable influence of the treatment on pain interference, such that treatment cases have lower (better) interference levels There is a reliable influence of the treatment on pain interference, such that treatment cases have higher (worse) interference levels There is no reliable influence of the treatment on pain interference, treatment and control cases have the same interference levels In addition to determining whether the treatment has a “statistically significant” impact on pain interference, researchers also want to determine the strength of the association. Find and interpret the Cohen’s d statistic (i.e., the standardized mean difference). Considering the value of the standardized mean difference, what size effect do we see (do not round the effect size)? Related Samples t-Tests The data for this assignment come from a study of an online chronic pain management program. A total of 167 individuals with chronic pain were assigned to a treatment protocol that involved participation in online support groups and various other activities designed to improve their coping strategies. At the start of the study, researchers collected a number of background variables (e.g., age, frequency of exercise, gender) and a 7-item depression scale. Individuals in the treatment group participated in the online pain management program for approximately 6 weeks. At the end of the intervention period, researchers administered the depression scale a second time. The table below provides detailed information about the variables in the data set. Variable Name Item Stem Response Scale MALE Respondent gender (0 = female, 1 = male) 0-1 AGE Respondent age 18-78 EXERCISE Frequency of exercise 1-8 DEPRESSPRE Pre-test scale score computed by summing 7 items 0-20 DEPRESSPOST Post-test scale score computed by summing 7 items 0-20 Perform a paired-samples t-test that compares pretest and posttest depression score means. Use a two-tailed hypothesis test. What is the null hypothesis for the analysis? Give the value from the printout that tells you how much scores changed from pretest to posttest on the 0 to 20 metric of data. Find and interpret the t statistic: Based on the probability value, what would you say regarding the null hypothesis? (i.e., do you have evidence in favor of or against the null?) Based on your response to the previous question, which of the following interpretations is correct? There is a decrease in depression scores due to the intervention There is an increase in depression scores due to the intervention Depression scores do not change from pre-test to post-test Write a one-sentence summary in APA format results from this test.
