Practical Data Management and Analysis for Public Health
The CDC recommends that people between the ages of 6 to 17 years engage in at least 60 minutes of moderate to vigorous physical activity per day, with vigorous physical activity on at least 3 days. Physical activity has numerous health benefits, including short-term increases in physical fitness and longer-term decreases in the risk of heart disease, type 2 diabetes, and some cancers. A large municipal school district is considering implementing a physical activity promotion program called “Don’t Just Sit There” in its high schools. The intervention is not cheap, however, and in a time of budget cuts the municipal education administration decides to conduct a randomized trial of the intervention in three high schools. The goal is to determine whether the intervention is effective in altering key psychosocial precursors to physical activity, increasing physical activity itself, and increasing physical fitness. The psychosocial factors of interest are (a) students’ self-efficacy to engage in moderate to vigorous physical activity during their free time on most days and (b) students’ perceived value of engaging in moderate to vigorous physical activity. Thus, a simple conceptual model for the intervention is as follows.
Self-efficacy
for physical
▬► activity ▬► Physical
DJST program activity ▬► Fitness
▬► Value-expectancy ▬► behavior
for physical
activity
The trial works as follows. Three schools are participating: Clara Barton High School, Frederick Douglas High School, and Harvey Milk High School. In each of these schools, administrators recruit 100 students and collect baseline data from them at the beginning of the school year. The baseline data include measures of self-efficacy, perceived value, and demographic factors assessed via a self-report questionnaire; physical activity is assessed by having each student wear an ActiGraph accelerometer for 1 week, and physical fitness is assessed via heart rate following a 3-minute step test administered to participants in each school’s nurse’s office. After baseline measurement is complete, students are assigned to either the treatment group or the control group via randomization. Treatment group members are then offered the Don’t Just Sit There intervention for 6 months, while control group members receive no intervention. At the end of the 6 months, the same procedures are used to assess the psychosocial, behavioral, and health variables again.
Assignment
In this assignment, you are tasked with working on the baseline data. You will be provided with three SPSS data sets (School1PRE.sav, School2PRE.sav, and School3PRE.sav) and a codebook (DJSTPreCodebook.doc). You are also given a copy of the questionnaire that students were asked to complete (DJSTquestionnaire.doc). The data sets contain the baseline data from the three study high schools, and the codebook and questionnaire contain all of the information you should need to make sense of these data. You are to use SPSS to carry out the following specific tasks:
1. Merge the three data sets into a single file, DJSTpre1.sav.
2. Obtain frequencies and/or descriptive statistics on all raw variables.
3. Following the value-expectancy framework, derive value-expectancies for each of the eight possible outcomes of physical activity (coping with stress, having fun, etc.). Do this by multiplying each expectancy variable (e.g., It would help me cope with stress) by the corresponding value variable (e.g., How positive or negative would you feel about coping well with stress). For example, VE1pre would be defined as A1pre•C1pre. The new variables VE1pre through VE8pre should have variable labels but do not need value labels.
4. Compute Cronbach’s alpha for the eight derived value-expectancy measures (VE1pre through VE8pre) and for the eight items measuring self-efficacy (B1pre through B8pre).
5. Derive a baseline value-expectancy scale score (VEpre) as the mean of the eight value-expectancy measures (VE1pre through VE8pre) and a baseline self-efficacy scale score (SEpre) as the mean of the eight self-efficacy indicators (B1pre through B8pre).
6. From HRpre, derive the ordinal variable HRCatpre so that students whose heart rate is less than 80 beats/minute are categorized as excellent (coded 1), those whose heart rate is between 80 and 90 are categorized as good (coded 2), those whose heart rate is between 90 and 110 are categorized as average (coded 3), those whose heart rate is between 110 and 120 are categorized as poor (coded 4), and those whose heart rate is greater than 120 are categorized as very poor (coded 5).
7. From either HRpre or HRCatpre, derive a dichotomous variable HRPoorpre so that students whose heart rate is below 110 beats/minute are categorized as not poor (coded 0) and those whose heart rates are greater than or equal to 110 are categorized as poor (coded 1).
8. Make sure that all newly derived variables from the previous steps have variable labels, and that HRCatpre and HRPoorpre have appropriate value labels.
9. Save the modified data set under the new name DJSTpre2.sav.
10. Obtain frequencies and/or descriptive statistics on the following derived variables: SEpre, VEpre, HRCatpre, and HRPoorpre.
11. Obtain subgroup-specific frequencies and/or descriptive statistics for each of the derived variables mentioned in Part 10, plus MALE, RACE, GRADE, SCHOOL, PHYSACTpre, and HRpre for the treatment and control groups.
12. Run pairwise correlations between SEpre, VEpre, PHYSACTpre, and HRpre.
13. Prepare a written report on the baseline data. That report should include two tables in which you collect the results from Task 2 of the assignment. One table should cover SCHOOL, MALE, RACE, GRADE, TREAT, PHYSACTpre, and HRpre. The second table should cover the questionnaire items A1pre through A8pre, B1pre through B8pre, and C1pre through C8pre. The report should also present information on the internal consistency (Task 4) of the baseline self-efficacy and value-expectancy scales, as well as the correlation between these two scales and baseline physical activity and heart rate (Task 12). Finally, the report should include a single table that presents treatment and control-group-specific frequencies and descriptive statistics for the raw and derived variables MALE, RACE, GRADE, PHYSACTpre, HRpre, SEpre, VEpre, HRCatpre, and HRPoorpre, along with your commentary on whether the randomization appears to have worked (i.e., whether the two groups appear to be similar on these variables).
The deliverables for this assignment are:
(1) An SPSS syntax file that accomplishes Tasks 1 through 12. The file should contain all of the commands necessary for accomplishing these tasks, in the specified order, and should not contain any extraneous commands.
(2) Your data set DJSTpre2.sav.
(3) Your written report as described in Task 13.
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