Exercise 29

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The t-test for dependent groups is a parametric analysis technique used to determine statistical differences between two related samples or groups. Groups are dependent or related because they were matched as part of the design to ensure similarities between the two groups and thus reduce the effect of extraneous variables. For example, two groups might be matched on gender so an equal number of males and females are in each group, thus reducing the extraneous effect of gender on the study results. The researcher’s decision to match groups is determined by the study being conducted and is detailed in the study design. In previous research, groups have most commonly been matched for age, gender, ethnicity, diagnoses, and status of illness. Matching the groups strengthens the study design by reducing the effect of extraneous variables controlled by matching. Groups are also dependent when scores used in the analysis are obtained from the same subjects under different conditions, such as pretest and posttest study design. In this type of design, a single group of subjects is exposed to pretest, treatment, and posttest. Subjects are referred to as serving as their own control during the pretest that is then compared with the posttest scores following the treatment. This is a weak quasi-experimental design since it is difficult to determine the effects of a treatment without comparison to a separate control group. The assumptions for the t-test for dependent groups are:

1. The distribution of scores is normal or approximately normally distributed. 2. The dependent variable(s) is (are) measured at interval or ratio levels. 3. The groups examined for differences are dependent based on matching or subjects serving as their own control.

4. The differences between the paired scores are independent

QUESTIONS TO BE GRADED.
1. What are the two groups whose results are reflected by the t ratios in Tables 2 and 3? 2. Which t ratio in Table 2 represents the greatest...
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