Case Study

Based on your understanding of sampling error, explain how the researcher should interpret the differences between these three sample means. Specifically, diagnose the cause of these variations and justify why the mean scores differ despite all three samples being selected randomly from the exact same population.

Case context: A clinical researcher draws three separate random samples of clinically depressed adults from the same population and calculates the mean number of depressive symptoms for each sample. The mean scores obtained are 8.738.73 for the first sample, 6.456.45 for the second sample, and 9.449.44 for the third sample.

Question: Based on your understanding of sampling error, explain how the researcher should interpret the differences between these three sample means. Specifically, diagnose the cause of these variations and justify why the mean scores differ despite all three samples being selected randomly from the exact same population.

Sample answer: The researcher should interpret these differing mean scores (8.738.73, 6.456.45, and 9.449.44) as a demonstration of sampling error. Since statistics are inherently subject to random variability, we expect statistical values to fluctuate randomly across different samples even when they are drawn from the identical population. The difference is not due to a change in the underlying population but is a natural consequence of selecting different random subsets of individuals.

Key points:

  • Diagnose the variations in the mean scores (8.738.73, 6.456.45, and 9.449.44) as sampling error.
  • Explain that statistical values naturally fluctuate across different samples from the same population.
  • Justify that the differences are due to random variability and do not indicate that the underlying populations are different.
  • Describe how statistics are inherently subject to random variability.

Rubric: The response should show comprehension of sampling error by diagnosing the variations as random fluctuations rather than systematic differences in the population. It should explain that random samples from the same population naturally vary due to inherent statistical variability, referencing the specific mean values provided.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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