Due Date: 11/03/05
Lab 9: Measuring Impact in the Class Project
Cross-sectional Study
This lab will use the data collected during a class project to determine whether
the video and flyer changed students’ knowledge and attitudes. Two data sets,
baseline (newbase03) and follow up (newfup03) are available on blackboard.
You are to download the files and run the steps to calculate impact. I’ll outline
the steps for you.
To turn in this lab, you need only answer the questions below, and don’t have to
include command or log files.
1. Append the 2 datasets. (Note: remember to create the “wave” variable
which indicates survey wave (0=baseline, 1=follow up). Report the sample
size for both waves.
2. Inspect the data, be sure to look for values that are outside the normal
range of expected answers (e.g., a “3” when there should be only 0, 1 and
2). Report any variables that needed recoding (Hint: the knowledge items
need to be recoded as being either correct or incorrect). Report the
baseline and follow-up means for q1-q14, and the five knowledge
questions q18-qq21.
3. Create the outcome variables.
a. Factor analyze q1 to q14. Determine the number of factors. Check
to see whether any of these items need to be recoded based on the
factor analytic results and the phrasing of the item (e.g., whether a
high score reflects either a positive or negative nutrition practice).
Finally, decide on a scaling method (Hint: we have been calculating
factor scores by taking the mean of all the items within the factor).
b. Create correct knowledge questions. Factor analyze them
separately and as one sample. Determine the number of factors
and decide on scaling method.
c. Create the appropriate factors and label them.
d. Report the means and standard deviations for baseline and followup.
4. Did scores change significantly between baseline and FU? Report
means, t-values and p values.
5. Did scores change significantly between baseline and FU for the
intervention classes? Create a dummy variable indicating intervention
classes (HP 200, 320, 400) and then conduct separate t-tests for each
group. Report means, t-values and p-values.
6. Did scores change more for those who reported seeing a flyer or watching
the video? (Hint: Run a regression model with VIDEO and FLYER as
predictor variables. Include baseline (wave=0) subjects into these
analyses by giving them a score of 0 for both VIDEO and FLYER).
7. Determine whether implementation or contamination issues affect the
results.
a. Cross tabulate condition by exposure to the video and exposure to the
flyer. What are you trying to find here? Was the intervention
implemented sufficiently? Report and describe your observations.
b. Correlate the outcomes on exposure to the video and to the flyer. Are
they correlated?
c. Regress the outcomes on exposure to a video or flyer in addition to
study condition. Does exposure explain any additional variance in the
outcomes?
d. Regress the outcomes on exposure to a video or flyer in addition to
study condition including controls for socio-demographic
characteristics (sex, year, ethnicity, major, health). Does exposure
explain any additional variance in the outcomes?