Formula used to calculate confidence interval..please give example. Thanks

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asked by Bryant
  1. For 95% confidence, mean ± (1.96 standard deviations)/sq rt. of n. For other levels of confidence, the number of standard deviations will vary. It indicates that, if we drew 100 samples, the true population mean will be within this range 95% of the time. Of course, the larger you n, the smaller the range of your estimate is.

    I'll let you think of an example.

    I hope this helps.

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    posted by PsyDAG
  2. Eric has computed that it takes an average (mean) of 17 minutes with a standard deviation of 3 minutes to drive from home, park the car, and walk to his job. One day it took Eric 21 minutes to get to work. You would use the formula for transforming a raw score in a sample into a z-score to determine how many standard deviations the raw score represents. Since his "score" is 21, you would subtract the mean of 17 from 21 and divide that result (4) by the standard deviation of 3. The z-score of 1.33 tells you that Eric’s time to get to work is 1.33 standard deviations from the mean.

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    posted by shonda

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