Information Technology Reference
In-Depth Information
CHAPTER ONE
ANOVA and Research Design
1.1 WHAT IS ANALYSIS OF VARIANCE?
Analysis of variance (ANOVA) is a statistical technique used to evaluate
the size of the difference between sets of scores. For example, a group of
researchers might wish to learn if the room color in which college students
are asked to respond to questions assessing their mood can affect their
reported mood. Students are randomly assigned to complete a mood
inventory in one of two rooms. Random assignment, one of the hallmarks
of experimental design, is used in an attempt to assure that there is no
bias in who is placed into which group by making it equally likely that any
one person could have been assigned to either group. One of the rooms
is painted a soft shade of blue that was expected to exert a calming effect
on the students; the other room is painted a bright red that was presumed
to be more agitating than calming. Higher numerical scores on the mood
inventory indicate a more relaxed mood. At the end of the study, we score
the mood inventory for all participants.
The research question in this example is whether mood as indexed by
the score on the mood inventory was affected by room color. To answer
this question, we would want to compare the mood scores of the two
groups. If the mood scores obtained in the blue room were higher overall
than those obtained in the red room, we might be inclined to believe that
room color influenced mood.
One way to start the comparison process is to take an average (a mean)
for each group of the responses to the mood questions and visually inspect
these two values. But comparing the scores between the groups in order
todrawaconclusionabouttheeffectofthecoloroftheroomonmoodis
not always going to be a simple matter. Among the related questions that
we face in doing the comparison are:
How much of a difference is there between the means?
How much overlap is there in the scores of the members of each
group?
Based on the difference in the means and the overlap in scores, is
the mean difference sufficiently large for us to say that room color
made a difference?
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