1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Confidence Interval Calculation

  1. Jan 14, 2014 #1
    See attached for problem

    Working:

    Mean: 1203.26
    Standard Deviation: 7.047

    for 99% confidence interval, level of significance = 0.01
    Therefore

    0.5 - 0.01/2 = 0.45
    Reading 0.45 from standard distribution table i get a value of 1.65

    therefore confidence interval should be

    1203.26 +/- (1.65*7.047)/√15

    1203.26 +/- 3

    however using this website to check my answer:

    http://www.mccallum-layton.co.uk/tools/statistic-calculators/confidence-interval-for-mean-calculator/ [Broken]

    It gives me a value of 5 (approx)

    Thanks
     

    Attached Files:

    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Jan 14, 2014 #2

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    For a (symmetric) 99% confidence on a quantity X, you want a 0.5% chance that X is below below the lower limit and a 0.5% chance that X is above the upper limit. In other words, if U is the upper limit you want Pr{ X ≤ U} = 1-0.005 = 0.995. What is the 99.5 percentile on the standard normal distribution?
     
    Last edited by a moderator: May 6, 2017
  4. Jan 14, 2014 #3
    Thanks for your reply, I'm not sure where the 0.005 value is from?
     
  5. Jan 14, 2014 #4

    Ray Vickson

    User Avatar
    Science Advisor
    Homework Helper

    What is meant by x%?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Confidence Interval Calculation
  1. Confidence Interval (Replies: 1)

Loading...