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Based on this scenario, diagnose the student's errors and explain the correct conceptual method for finding the median of both the original seven-score dataset and the new eight-score dataset.
Case context: A student researcher is examining response times in a cognitive psychology task. They collect the scores of seven participants: , , , , , , and seconds. Without sorting the data, the student identifies the middle score in the raw list () as the median. Later, when an eighth participant is added with a score of , the student incorrectly calculates the median by taking the average of the raw list's middle values.
Question: Based on this scenario, diagnose the student's errors and explain the correct conceptual method for finding the median of both the original seven-score dataset and the new eight-score dataset.
Sample answer: The student's primary error is failing to rearrange the scores from lowest to highest before locating the median. Conceptually, the median must divide the ordered distribution into two equal halves. For the seven scores, once arranged to (, , , , , , ), the middle score is . When the score of is added to create an even dataset, the ordered scores are (, , , , , , , ). There are two middle values, and , meaning the median must be the value halfway between them, which is .
Key points:
- Identify the error of not sorting the raw dataset.
- Order the raw scores to (, , , , , , ) and locate the median of .
- Identify that adding a score of creates an even number of scores.
- Find the two middle values ( and ) of the ordered even dataset and calculate the median () halfway between them.
Rubric: Grading criteria: 1. Clearly identify that the student failed to sort the scores before locating the middle value. 2. Correctly describe the sorting step and identify the correct median of for the odd dataset. 3. Correctly describe the method for an even dataset, identifying the two middle values as and , and finding the value halfway between them ().
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Research Methods in Psychology - 4th American Edition @ KPU
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