This study investigates whether there are
differences in the outcomes of three different treatments for anxiety. The
treatment conditions that are compared are treatment with medication, treatment
with psychotherapy, and placebo (inactive pills). In addition, we want to see
if gender of the client moderates the effects of the treatment. Every
participant had been diagnosed with similar types and severity of anxiety
disorders when they entered the study. Each participant was randomly assigned
only to one of the three treatment conditions. After 12-weeks of treatment (or
placebo), all participants completed two questionnaires to measure worry and
general emotion. The higher the scores on these measures, the higher the
anxiety level of the participant.
Directions:
The factorial MANOVA
will combine what you have learned previously about
1. Post hoc tests when you have more than two
groups on an IV (one-way ANOVA),
2. Main effects and interactions (factorial ANOVA),
and
3. Working with multivariate analyses of multiple
DVs (one-way MANOVA).
Using the SPSS data file for Module 6 (located
in Topic Materials), answer the following questions:
1. What are the independent variables in this
study? What are the dependent variables?
2. Why is a factorial MANOVA appropriate to use for
this research design?
3. Did you find any errors that the researcher made
when setting up the SPSS data file (don’t forget to check the variable
view)? If so, what did you find? How did you correct it?
HINT:
Yes,
there are coding errors for Measures.
4. Perform Initial Data Screening. What did you
find regarding missing values, univariate outliers, multivariate outliers,
normality?
HINT:
Revisit
instructions from last module’s readings on how to compute Mahalanobis distance
and then analyze for multivariate outliers.
5. Perform a factorial MANOVA on the data. Before
interpreting the multivariate results of the MANOVA, check outcomes that test
other assumptions for this statistic: equality of covariance matrices (see
Box’s Test) and sufficient correlation among the DVs (see Bartlett’s Test of
Sphericity). Also check the results of the Levene’s Test of Equality of Error
Variances to evaluate that assumption for the univariate ANOVAs that are run
and show in the Tests of Between-Subjects Effects output. What have you found
about whether the data meet these additional assumptions for the MANOVA and
follow-up ANOVAs? Explain.
HINTS:
· Once in the Options box, remember to check box
for “Residual SSCP matrix” to get results for the Bartlett’s test.
· Also, remember to ask for post hoc tests for
Treatment because there are more than two conditions. Profile plots also help
with visualizing interactions.
6. What are the outcomes of the multivariate tests
(main effects and interaction)? Report either the Pillai’s Trace or Wilks’s
Lambda for each result, as well as the associated F-value and its statistical
significance. Use the following format for notation to report each result:
Pillai’s Trace OR Wilks’ lambda = ____; F(df, df) = ____, p= ____.
HINTS:
· Use Pillai’s trace if there are problems with
heterogeneity of variance-covariance matrices for the DVs. Otherwise, Wilks’
lambda is fine.
· Eta squared cannot be calculated from the information
provided in the multivariate tests results.
7. Given the results of the multivariate tests,
would you now move on to interpret the results of the Tests of Between-Subjects
Tests? If yes, what are the results and what do they mean? (Report each of the
results using the format of F(df,
df) = _____, p= _____ ,h2= _____.)
8. Because one IV has more than two conditions, you
would need to do post hoc tests if the overall F-value was statistically
significant. If so, what results did you find?
9. If you had a significant interaction effect,
what follow-up tests do you need to perform to understand how gender moderates
the effects of treatment? What are the results?
10.Citing the results of your statistical analyses, what is the conclusion
you can draw (and support) regarding research question that was posed in this
research (see problem statement)?
HINT:
Use the sample results write-up in the textbook to see what you should report
and how to say it. Just substitute the correct language and values for the
analyses you have done for this problem.
