An investigator conducts an experiment involving the effects of three levels of a drug on memory. Subjects are randomly assigned to one of three conditions. A different drug level is administered in each condition. Memory is measured 10 minutes after each subject receives the drug. The following scores are recorded. The higher the score, the better the memory. ΣS_within = _________. A) 62.25 B) 59.75 C) 56.65 D) 57.00

Question

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To find the within-group sum of squares (SS), we first need to find the mean for each condition: Mean for condition 1 = (17+13)/2 = 15 Mean for condition 2 = (12+16)/2 = 14 Mean for condition 3 = (13+11)/2 = 12 Next, we calculate the sum of squares for each condition: SS for condition 1 = (17-15)² + (13-15)² = 4 + 4 = 8 SS for condition 2 = (12-14)² + (16-14)² = 4 + 4 = 8 SS for condition 3 = (13-12)² + (11-12)² = 1 + 1 = 2 Finally, we add up the SS for each condition to get the within-group SS: SS within = 8 + 8 + 2 = 18 We had a total of 18 subjects in the study, and there were 3 conditions, so the degrees of freedom for the within-group SS is: df within = 18 - 3 = 15 Using these values, we can calculate the mean square (MS) for the within-group SS: MS within = SS within / df within = 18 / 15 = 1.2 Therefore, ΣS_within = (n-3)×MS within = 15×1.2 = 18.

An Investigator Conducts an Experiment Involving the Effects of Three