Tests of Differences between Means, Dependent Means (2 of 4)

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The first step in testing the difference between means is to compute a difference score for each subject. The difference score is simply the difference between the two conditions. The difference scores are shown below:

Sub   Visual   Auditory   Vis-Aud
 1      420       380        40
 2      235       230         5
 3      280       300       -20
 4      360       260       100
 5      305       295        10
 6      215       190        25
 7      200       200        00
 8      460       410        50
 9      345       330        15
10      375       380        -5
Mean    319.5     297.5      22
Notice that the difference between the visual mean (319.5) and the auditory mean (297.5) is the same as the mean of the difference scores (22). This will always be the case: The difference between the means will always equal the mean of the difference scores. The significance test of the difference between means consists of determining whether the mean of difference scores is significantly different from zero. If it is, then the difference between means is significant. The procedure for testing whether a mean is significantly different from zero is given in the section "Tests of µ, standard deviation estimated."

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