Case Study

Explain what this interval indicates about the true mean calorie estimate for the population of university students, and justify whether a hypothesized population mean of 250250 is statistically significantly different from the sample mean.

Case context: A psychology researcher conducts a study on calorie estimation where a sample of 2020 university students provides a mean calorie estimate for a cookie of 200200, with a 95%95\% confidence interval ranging from 160160 to 240240.

Question: Explain what this interval indicates about the true mean calorie estimate for the population of university students, and justify whether a hypothesized population mean of 250250 is statistically significantly different from the sample mean.

Sample answer: The interval indicates that there is a high probability (95%95\%) that the true mean calorie estimate for the entire population of university students falls somewhere between 160160 and 240240. A hypothesized population mean of 250250 is statistically significantly different from the sample mean at the .05.05 alpha level because 250250 falls outside the 160160 to 240240 confidence interval range.

Key points:

  • Explains that the interval of 160160 to 240240 represents a range where the true population mean falls with a high probability (95%95\%).
  • Comprehends that the interval allows for hypothesis testing of population means.
  • Justifies that a population mean of 250250 is statistically significantly different because it is outside the interval.
  • Associates the significance testing of the boundary limits with the .05.05 alpha level.

Rubric: The explanation must show comprehension of the confidence interval as representing a high probability (95%95\%) range for the true population mean, and justify the significance of the hypothesized value of 250250 based on its location outside this range at the .05.05 level.

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Updated 2026-05-27

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Research Methods in Psychology - 4th American Edition @ KPU

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