14.6 Writing Up the Results
In writing up the results of this experiment we could simply say:
To investigate the effects of relaxation therapy on the severity of migraine headaches,
9 participants rated the severity of headaches on each of two weeks before receiving
relaxation therapy and for three weeks while receiving therapy. An overall analysis
of variance for repeated measures showed a significant difference between weeks
(F(4,32) 5 85.04, p ,.05). The mean severity rating during baseline weeks was 22.166,
which dropped to a mean of 7.296 during training, for a difference of 14.87. A contrast
on this difference was significant (t(32) 5 18.21, p,.05). Using the standard deviation
of contrast differences for each participant produced an effect size measure of d 5 5.97,
documenting the importance of relaxation therapy in treating migraine headaches.
14.7 One Between-Subjects Variable and One Within-Subjects Variable
Consider the data presented in Table 14.4. These are actual data from a study by King
(1986). This study in some ways resembles the one on morphine tolerance by Siegel (1975)
that we examined in Chapter 12. King investigated motor activity in rats following injection
of the drug midazolam. The first time that this drug is injected, it typically leads to a distinct
decrease in motor activity. Like morphine, however, a tolerance for midazolam develops
rapidly. King wished to know whether that acquired tolerance could be explained on the
basis of a conditionedtolerance related to the physical context in which the drug was ad-
ministered, as in Siegel’s work. He used three groups, collecting the crucial data (presented
in Table 14.4) on only the last day, which was the test day. During pretesting, two groups of
animals were repeatedly injected with midazolam over several days, whereas the Control
group was injected with physiological saline. On the test day, one group—the “Same”
group—was injected with midazolam in the sameenvironment in which it had earlier been
injected. The “Different” group was also injected with midazolam, but in a differentenvi-
ronment. Finally, the Control group was injected with midazolam for the first time. This
Control group should thus show the typical initial response to the drug (decreased ambula-
tory behavior), whereas the Same group should show the normal tolerance effect—that is,
they should decrease their activity little or not at all in response to the drug on the last trial.
If King is correct, however, the Different group should respond similarly to the Control
group, because although they have had several exposures to the drug, they are receiving it in
a novel context and any conditioned tolerance that might have developed will not have the
necessary cues required for its elicitation. The dependent variable in Table 14.4 is a measure
of ambulatory behavior, in arbitrary units. Again, the first letter of the name of a variable is
used as a subscript to indicate what set of means we are referring to.
Because the drug is known to be metabolized over a period of approximately 1 hour,
King recorded his data in 5-minute blocks, or Intervals. We would expect to see the effect
of the drug increase for the first few intervals and then slowly taper off. Our analysis uses
the first six blocks of data. The design of this study can then be represented diagrammati-
cally as shown in next page.
Here we have distinguished those effects that represent differences between subjects from
those that represent differences within subjects. When we consider the between-subjects
term, we can partition it into differences between groups of subjects (G) and differences
between subjects in the same group (Ss w/in groups). The within-subject term can similarly
Section 14.7 One Between-Subjects Variable and One Within-Subjects Variable 471
