Troubleshooting
Problem
Can you provide an example of a crossover design, which shows how to set up the data and perform the analysis in SPSS?
Resolving The Problem
Pasted below, we provide an annotated command syntax file that reads in a sample data file and performs the analysis. The data is structured for analysis as a repeated measures ANOVA using GLM: Repeated Measures. Both the experiment and the data are hypothetical.
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* The following commands read in a sample data file
from a hypothetical crossover design.
* There are two levels of the between-subjects factor ORDER:
(1) placebo-first and supplement-second; and
(2) supplement-first and placebo-second.
* There are two dependent variables:
(1) PLACEBO, which is the response under the placebo
condition; and
(2) SUPPLMNT, which is the response under the supplement
condition.
* Both dependent variables are deviations from each subject's
baseline measurement.
DATA LIST FREE
/ order placebo supplmnt .
BEGIN DATA
1 -1.0 1.0
1 -0.5 1.0
1 -0.5 0.5
1 -0.5 0.5
1 0.5 1.5
1 0.5 1.0
1 0.5 0.5
1 1.0 1.0
2 -0.5 0.5
2 1.0 1.0
2 0.5 0.5
2 0.0 0.5
2 1.0 1.5
2 1.0 1.0
2 0.5 0.5
2 1.0 1.0
END DATA.
FORMATS order placebo supplmnt(F3.1) .
* Set up a repeated measures model defining one two-level
Within-Subject (WS) factor, named TREATMNT.
* PLACEBO and SUPPLMNT are the dependent measures and
ORDER is the between-subjects factor.
GLM
placebo supplmnt BY order
/WSFACTOR = treatmnt 2 Polynomial
/METHOD = SSTYPE(3)
/PLOT = PROFILE( treatmnt*order )
/CRITERIA = ALPHA(.05)
/WSDESIGN = treatmnt
/DESIGN = order .
* There is a significant main effect for TREATMNT,
F(1,14) = 16.2, p < .001.
* Inspection of the Profile Plot shows that both groups
had higher average values for the dependent variable
following the supplement condition (TREATMNT = 2) than
following the placebo condition (TREATMNT = 1).
* The TREATMNT*ORDER interaction is significant,
F(1,14) = 5.0, p < .05.
* Further inspection of the Profile Plot suggests that
subjects in the ORDER = 2 group--for which the supplement
condition preceded the placebo condition--showed a higher
average response following the placebo condition than did
the ORDER = 1 group.
* This finding suggests that there was a carryover of
benefits from initial administration of the supplement.
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Related Information
Historical Number
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Modified date:
16 April 2020
UID
swg21479623