Math Problem Statement

Don't construct a confidence interval: A psychology professor at a certain college gave a test to the students in her class. The test was designed to measure students' attitudes toward school, with higher scores indicating a more positive attitude. There were 30 students in the class, and their mean score was 78. Scores on this test are known to be normally distributed with a standard deviation of 10. Explain why these data should not be used to construct a confidence interval for the mean score for all the students in the college.

Solution

These data should not be used to construct a confidence interval for the mean score of all the students in the college because the sample of students is not representative of the population of all students in the college. Here are the reasons:

  1. Sample Bias: The sample consists only of the students in one psychology professor's class. These students may not represent the broader student body due to factors such as differences in academic programs, interests, or exposure to the professor's teaching style.

  2. Population Scope: The test scores are only from a specific subset (the professor's class) rather than a random or diverse sample from the entire student population. For a confidence interval to be valid, the sample should ideally be randomly selected to ensure that it reflects the characteristics of the whole population.

  3. Potential Influence of Context: The professor's own teaching methods or the class environment may have influenced the students' attitudes, leading to scores that do not generalize beyond that class.

  4. Sample Size Limitation: While the sample size of 30 is sufficient for constructing a confidence interval under normal distribution assumptions, the lack of randomness in the sample selection undermines its validity for population-level inferences.

  5. Representation of Variability: The attitudes of students across the college may have a different mean or standard deviation than those in the psychology professor's class. Without a proper sampling method, we cannot account for this variability.

Conclusion:

To construct a valid confidence interval for the mean score of all college students, the data must come from a sample that is randomly selected and representative of the entire population. Since this criterion is not met, these data are unsuitable for this purpose.

Would you like to dive deeper into sampling methods or the implications of sample bias?


Related Questions:

  1. What is the importance of random sampling in statistical inference?
  2. How does sample size affect the reliability of a confidence interval?
  3. Can data from a biased sample ever be adjusted to approximate population parameters?
  4. What statistical tests can verify if a sample represents a population?
  5. Why is normality important in constructing confidence intervals?

Tip:

Always assess whether your sample is random and representative before making population-level inferences using statistical methods.

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Math Problem Analysis

Mathematical Concepts

Statistics
Confidence Intervals
Sampling Bias

Formulas

Confidence interval formula: CI = x̄ ± Z*(σ/√n)

Theorems

Central Limit Theorem
Law of Large Numbers

Suitable Grade Level

Grades 11-12 and college-level