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STAT 135 LAB 12

STAT 135 LAB 12. Learning Objective: #77 TA: Dongmei Li. Confidence Interval (CI). A confidence interval is an interval calculated from sample data that will capture the true population parameter. 95% is the most commonly used. How to find CI for p.

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STAT 135 LAB 12

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  1. STAT 135 LAB 12 Learning Objective: #77 TA: Dongmei Li

  2. Confidence Interval (CI) • A confidence interval is an interval calculated from sample data that will capture the true population parameter. • 95% is the most commonly used.

  3. How to find CI for p 1. Identify population proportion (p), sample proportion ( ) and sample size (n). 2. Calculate std. dev. of sampling distribution. => 3. Find the critical value z* from Table 21.1. 4. Calculate a Confidence interval. =>

  4. Example to find CI • Suppose I want to find the percentage of teenagers who watch TV more than 3 hours per day in Ohio. I did a survey in Ohio and found that 20 teenagers among those randomly selected 100 teenagers watch TV more than 3 hours per day. • Make a 95% Confidence interval for percentage of teenagers who watch TV more than 3 hours per day in Ohio.

  5. What CI means? • If we repeatedly take many samples and construct 95% CI for each sample. • Then the true proportion will be in 95% of the intervals.

  6. Confidence interval • There is a trade-off between confidence and precision. • You have to sacrifice precision if you want more confidence. • The higher confidence level (the more confident), the wider confidence interval (the less precise).

  7. Learning objective for Lab 12 • 77. There is a trade-off between confidence and reliability. In order to achieve a higher level of confidence, you must be willing to accept a larger margin of error (a wider interval) or pay the price of a larger sample size.

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