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Session 6, Part C:
Comparative Experimental Studies
In This Part: Measuring Short-Term Recall | An Experiment | Experimental Design
Analysis of the Experiment
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Sixteen subjects participated in the memory experiment using Design 5. Eight subjects were randomly assigned to each group. Each subject in Group 1 was first measured using List A. Then each subject in Group 1 was measured using List B. The order was reversed for Group 2: The subjects were first measured using List B, then List A. Here are the measurements from the experiment:
Because every subject was measured using both List A and List B, it is of interest to look at the differences in the subjects' scores (Score A - Score B), which are shown in the last column.
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Problem C7 |  |
a. | Determine the Five-Number Summary for the 16 scores using List A. |
b. | Determine the Five-Number Summary for the 16 scores using List B. |
c. | Using the same scale, sketch the two box plots for List A and List B side by side. |
d. | Based on the summaries and box plots, how do scores using List A compare with scores using List B? |
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The comparison of the two box plots indicates that the scores of subjects using List A tend to be higher than the scores of subjects using List B; therefore, subjects recalled words more readily than they recalled non-words. The difference in the two medians (10 - 5 = 5) indicates that people can typically recall five more words than non-words. However, there is somewhat more variation in the scores from List A (words) than from List B (non-words); the range for List A is 12 compared to 8 for List B, and the IQR for List A is 3 compared to 2 for List B.
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This comparative analysis does not take into account the advantage you gain from pairing each subject's scores from both lists and then examining the difference between the two scores (Score A - Score B). A positive difference occurs when the List A score is higher than the List B score; that is, the difference is positive when memory recall is better for words than for non-words. Note 7
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Problem C8 | |
Examine the column of differences in the Number Recalled Correctly table:
a. | How many of the differences are positive? How many are negative? |
b. | What does this suggest about memory recall of words versus non-words? |
c. | Determine the Five-Number Summary of the 16 differences. |
d. | Sketch the box plot of the differences. |
e. | Based on the Five-Number Summary and box plot of the differences in scores between the two lists, how do scores using List A compare with scores using List B? |
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