Find the 90% two-sided confidence interval for the mean score.

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SUMMARY

The discussion centers on calculating the 90% two-sided confidence interval for the mean score of a sample of 12 students with grades following a normal distribution. The provided scores are: 59, 84, 68, 93, 49, 77, 82, 75, 81, 58, 70, and 80. Given the sample size, the Student's t-distribution is recommended for this calculation due to the unknown population variance. Additionally, the validity of the normal distribution assumption is questioned based on the grading system's constraints.

PREREQUISITES
  • Understanding of confidence intervals and their significance
  • Familiarity with the Student's t-distribution
  • Basic statistical concepts such as mean and variance
  • Knowledge of sample size implications in statistical analysis
NEXT STEPS
  • Learn how to calculate confidence intervals using the Student's t-distribution
  • Study the implications of sample size on statistical inference
  • Explore the differences between normal distribution and Student's t-distribution
  • Investigate the assumptions underlying normal distribution in grading systems
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Students, educators, and statisticians interested in statistical analysis, particularly in calculating confidence intervals and understanding the implications of sample distributions.

ianrice
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The distribution of grades is know to follow a normal distribution, but the mean and variance are unknown. A random sample of 12 students produced the following scores:

59, 84, 68, 93, 49, 77, 82, 75, 81, 58, 70, 80

Find the 90% two-sided confidence interval for the mean score.
 
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ianrice said:
The distribution of grades is know to follow a normal distribution

Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed.

Of course, perhaps this is a homework problem where such technicalities are ignored. If so, you should post it somewhere in the "Homework & Coursework Questions" section of the forum and show your attempt at solution.
 
"Does this grading system allow negative grades? If not, the the grades can't actually be normally distributed."

Nothing is ever really normally distributed: if the standard deviation is small enough then to a very good approximation the normal distribution can be quite useful.
 
You might consider a Student's t-distribution
 

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