1 / 8

Confidence Intervals

Confidence Intervals. By Rebekah Thomas. Confidence Intervals. Intervals that estimate population parameters and margins of error Estimation is based on sample means or proportions Example: I am 90% confident that the true average number of calories per cookie is somewhere on the

elaina
Download Presentation

Confidence Intervals

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Confidence Intervals By Rebekah Thomas

  2. Confidence Intervals • Intervals that estimate population parameters and margins of error • Estimation is based on sample means or proportions Example: I am 90% confident that the true average number of calories per cookie is somewhere on the interval (142.87, 150.13).

  3. Confidence intervals for PROPORTIONS Conditions: SRS? Normal? n( )≥10 & n(1 - )≥10 Independent? 10% rule • Margin of error • Standard deviation

  4. Confidence Intervals for MEANS z* or t*? Usually t* If n> 3o and is known, use z* • If n < 30 or is unknown, use t* • Remember to use df for t* df = n-1

  5. Finding an interval Calculate a 95% confidence interval for the true average temperature in April for Sandy, Utah. http://weather-warehouse.com/WeatherHistory/PastWeatherData_Alta_Sandy_UT_April.html Proportions or means? n = 25 = 34.024 °F S = 3.794 C=0.95

  6. n = 25 = 34.024 °F S = 3.794 C=0.95 Check conditions: 1. SRS? 2. Normal? n≥30 3. Independent? 10% rule Use t* since it’s means and st. dev. is unknown. I am 95% confident that the true average temperature in April in Sandy, Utah is somewhere on the interval (32.458 °F, 35.59 °F). Interpreting confidence level: 95% of all possible samples of size 25 from the population will result in an interval that captures the true average temperature in April.

  7. Sources http://sph.bu.edu/otlt/MPH-Modules/BS/BS704_Confidence_Intervals/BS704_Confidence_Intervals_print.html https://www.google.com/search?q=standard+deviation+symbol&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&hl=en&tbm=isch&source=og&sa=N&tab=wi&ei=Out6UemgFsjBrQHm1IGADA&biw=1294&bih=749&sei=Rut6Uf6NLIrlrQGEyIGQAQ#imgrc=_ My notes

More Related