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Confidence Interval

Confidence Interval. Proportions. Remember. Point estimate is different every time since it depends on the sample selected. In choosing a confidence interval, it is not a single point but rather an interval of reasonable values. Confidence Interval.

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Confidence Interval

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  1. Confidence Interval Proportions

  2. Remember • Point estimate is different every time since it depends on the sample selected. • In choosing a confidence interval, it is not a single point but rather an interval of reasonable values.

  3. Confidence Interval • Interval of reasonable values for the characteristic chosen with a degree of confidence. • The value of the population characteristic will likely be between the upper and lower bounds.

  4. Confidence Level • This represents the success rate of the method used to construct the interval. • If I repeat the process over & over, approximately this % of the intervals will contain the true parameter.

  5. Remember – for sampling distributions of proportions…. • It’s approximately normal if

  6. So, if I want to be 95% confident that my interval contains the true proportion, how many deviations would I be from the mean proportion?

  7. So what’s the critical z value that corresponds to a 98% confidence.

  8. So what’s the formula for a Confidence Interval?

  9. PANIC! • P – Parameter (tell what we are estimating) • A – Assumptions • N – Name the Formula • I – Interval (calculate it) • C - Conclusion

  10. When 320 college students were surveyed, 125 said they own their car. Construct a 90% confidence interval for the proportion of college students who own their car.

  11. Explain what the 90% confidence level means. If I repeat this process over & over, 90% of the intervals found will contain the true population proportion of households that own at least one gun.

  12. A survey of 2450 golfers showed that 281 of them are left handed. Construct a 90% and 98% confidence level.

  13. Homework • Worksheet

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