An experimental psychologist wanted to test two hypotheses. The first hypothesis proposed that stress would adversely affect the rate of serial learning. The second hypothesis proposed that the type of material (meaningless vs. meaningful) would moderate the effect of stress. The psychologist formed six groups by manipulating stress (A) at three levels — Low, Moderate and High — and Type of material (B) at two levels. The subjects were randomly assigned to these groups from an initial pool of subjects. A list of 15 CVC trigrams constituted meaningless material and a list of 15 three-lettered meaningful words constituted meaningful material. The number of trials required to learn the list was the dependent variable. The data were analysed by suitable analysis of variance. Selected findings: (1) The ratio of largest to smallest standard deviations for the six groups was reasonably close to one. (2) The degrees of freedom for error variance was 135. (3) The F ratio for the effect of stress was 0.95. (4) The effect sizes for each effect were calculated both by obtaining eta square and partial eta square.
The above design can best be labelled as:
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Correct answer: C. Randomized 3 × 2 unbalanced factorial design
Explanation
Error df = N − 6 = 135, so N = 141, which cannot split equally into 6 cells — a randomised 3 × 2 unbalanced factorial design.
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