Purchase Solution

Confidence interval and sample size

Not what you're looking for?

Ask Custom Question

1) Suppose that 64 smokers were sampled. Assume the sample mean and the sample standard deviation remained the same ($20 and $5, respectively).

a. What is the 95% confidence interval estimate of u?

b. A research a firm a conducted a survey to determine the mean amount of steady smokers spend on cigarettes during a week. A sample of 49 steady smokers revealed that X = $20 and s= $5. What is the 95% confidence interval estimate of u?
Explain why this confidence interval is narrower than the one determined in the previous exercise.

Purchase this Solution
Solution Summary

The confidence interval for different sample sizes have been calculated.

Solution Preview

1) Suppose that 64 smokers were sampled. Assume the sample mean and the sample standard deviation remained the same ($20 and $5, respectively).

a. What is the 95% confidence interval estimate of u?

Confidence limits

Mean=M = $20
Standard deviation =s= $5
sample size=n= 64
sx=standard error of mean=s/square root of n= 0.625 = ( 5 /square root of 64)
Confidence level= 95%
Therefore Significance level=alpha (a) = 5% =100% -95%
No of tails= 2
This is 2 tailed because we are calculating the 2 sided confidence interval for the average income

...

Purchase this Solution
Free BrainMass Quizzes
Know Your Statistical Concepts

Each question is a choice-summary multiple choice question that presents you with a statistical concept and then 4 numbered statements. You must decide which (if any) of the numbered statements is/are true as they relate to the statistical concept.

Terms and Definitions for Statistics

This quiz covers basic terms and definitions of statistics.

Measures of Central Tendency

Tests knowledge of the three main measures of central tendency, including some simple calculation questions.

Measures of Central Tendency

This quiz evaluates the students understanding of the measures of central tendency seen in statistics. This quiz is specifically designed to incorporate the measures of central tendency as they relate to psychological research.

View More Free Quizzes
Related BrainMass Solutions

  • Confidence interval

    One of the scaled items has a mean equal to 82 and a standard deviation of 12. Construct and interpret 95% and 99% confidence intervals. Assume that the investigators increased their sample size to 100.

  • Confidence interval for mean

    Answer The confidence interval is given by Sample Size 50 Confidence Interval Estimate for the Mean Data Sample Standard Deviation 27 Sample Mean 86 Sample Size 50 Confidence Level 95.5% Intermediate Calculations Standard Error of

  • Confidence Interval & Sample Size

    of confidence interval and sample size.

  • Confidence Interval Concepts

    (b) Increase the sample size When the sample size (n) increases, the margin of error will decrease and hence the width of the confidence interval decreases. That is, the width of the confidence interval decreases as the sample size increases.

  • Confidence Interval & Sample Size

    291887 Confidence Interval & Sample Size for a Random Sample 1 (b).

  • Finding Sample Amount for Population Mean

    Means and confidence intervals Answers a.

  • Calculating a Confidence Interval

    What is necessary to determine the sample size? To calculate a confidence interval, we need the same mean, sample standard deviation, sample size, and the desired level of confidence.

  • Sample Distribution Scenario Questions

    Confidence interval for proportion is given by where p = 120/200 = 0.60 Confidence Interval Estimate for the Proportion     Data   Sample Size 200 Number of Successes 120 Confidence Level 95%     Intermediate Calculations Sample Proportion

  • Sampling distribution of the sample mean is approx normal

    Increase the sample size and decrease the confidence level. Decreasing the confidence interval will reduce the confidence interval.

  • Probability Problem Set

    Repeat part (a) with a sample size of 10. d. Describe what happens to the confidence interval estimate when the sample size decreases. 3. a) The critical value for 95% confidence interval is 1.96.

View More Related Solutions