Due Date: 11/11/05
PM 536:
Lab 10: Measuring Impact in a Class Project
Panel Data
This lab will use data collected in a previous class project and you will determine
whether the video and flyer changed students’ knowledge, attitudes, and
practices. Two data sets, baseline (newbase03) and follow up (newfup03), were
used in Lab 9, so you should already have these files downloaded. Your task is
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. Merge the 2 datasets using the variable “ssn”. (NB: cases with missing
“ssn” can merge successfully since they “match”). Report the sample sizes
for number successfully merged, number baseline only and number follow
up only. Create a variable called “casetype” that indicates each case’s
status.
2. Create the outcome variables. In this analysis let’s create an attitude
scale that is the average score on q1 through q14 separately for baseline
and follow up; and a knowledge index separately for baseline and
followup. Report the means and standard deviations for the 2 attitude
scales and the 2 knowledge indices.
3. Create two difference scores (attitude & knowledge). Did scores change
significantly between baseline and FU? Report means, t-values and p
values.
4. Did scores change significantly differently for men or women? Did scores
change significantly differently for control and intervention classes (recall
the intervention classes were HP 200, 320, 400)? Report mean difference
score for the control and intervention groups, and the t-values and p
values for these difference scores.
5. Did scores change more for those who reported seeing a flyer or watching
the video? (Hint: Use the flyer and video FOLLOWUP variables as the
independent variable, NOT the baseline ones).
6. Determine whether attrition influenced our results by comparing those lost
to follow up on ethnicity, year in school, major and gender. Report your
results in a table with the relevant means and statistical tests.
7. Determine whether the intervention was effective by completing the table
below.
a. Regress the outcomes on whether the subjects was in the intervention
of control condition. Report the standardized beta coefficients, tvalues, and p-values in the table.
b. Regress the outcomes on exposure to a video or flyer in addition to
study condition. Does exposure explain any additional variance in the
outcomes?
8. Determine whether selectivity influenced our results by regressing
program exposure (video and flyer recall) on the control variables. (Hint:
this would be the same as the table except that video recall and then flyer
recall are the outcomes. Hint 2: video and flyer recall are dichotomous
variables so there is a different statistical technique.)
9. Was there a “recency” effect? Recall that the video was shown and flyer
distributed later in HP 400 than in HP 200 than in HP 320 (see table
below).
Table. Data collection and intervention dates for PM 536 study.
Class
HP 200
HP 300
HP 320
HP 340
HP 400
HP 420
Days
T/Th
M/W
Thur
M/W
M/W
M/W
Condition
I
C
I
C
I
C
Baseline
9/23
9/22
9/25
9/22
9/22
9/22
Intervention Followup
10/7
10/21
10/20
10/2
10/23
10/20
10/13
10/20
10/20
10. Write a 350 word description (approx. 1.5 pages) of the intervention’s
effects (or lack thereof) describing whether it worked, what evidence
supports or refutes this claim and what caveats or stipulations should be
placed on this interpretation.
Table 1. Effects of a nutrition promotion on attitudes and knowledge
(N=119).
Attitude
Knowledge
Baseline Attitude
Baseline Knowledge
School Year (ref: freshman)
Sophomore
Junior
Senior
Ethnicity
African American
Asian American
Hispanic/Latino
Male
HP Major
Intervention
Saw Video
Saw Flyer
R2
+p<.05; *p<.01; **p<.001