STS 110 Lecture Notes - Lecture 19: Sample Size Determination
27 Apr 2018
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STS 110!
Confidence Intervals!
1- Understand a confidence interval!
2- Understand a confidence level!
3- Be able to construct a confidence interval on stat crunch !
4- Interpreting a confidence interval !
1- Understand a confidence interval !
-Recall: !
-N: sample size!
-x: Sample mean !
-U: population mean !
-Always list confidence interval as (lower limit, upper limit) !
-The best way to estimate a mean is by adding and subtracting the
margin of error from the sample mean!
-ALWAYS USE UNITS!
-EX1: Sample mean weight is 160 lbs!
-Margin of error = 5 lbs!
-Sample size = 50 women!
-(155 lbs, 165 lbs) !
-EX2: A confidence interval to estimate heights of men is given by (65 in,
72 in)!
-1- Find sample mean: 68.5 in!
-2- Find margin of error: 3.5 in!
-3- Find population mean: cannot find!
-4- Find sample size: cannot find!
2- Understand a confidence level !
- A percentage assigned to a confidence interval that locates how well it
estimates the population mean !
-EX 1: Estimate weights of women at Elon.!
-1) (140 lbs, 142 lbs)!
-2) (130 lbs, 150 lbs) !
-3) (100 lbs, 200 lbs) <— best estimate…!
-4) (0 lbs, 50 lbs) !
-You generally want to be between 90% and 99% to provide a good and
strong confidence interval !
-Fact 1: As confidence level increases, the width of the interval
increases, so the margin of error also increases
find more resources at oneclass.com
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Document Summary
3- be able to construct a con dence interval on stat crunch. Always list con dence interval as (lower limit, upper limit) The best way to estimate a mean is by adding and subtracting the margin of error from the sample mean. Ex1: sample mean weight is 160 lbs. Ex2: a con dence interval to estimate heights of men is given by (65 in, 2- find margin of error: 3. 5 in. A percentage assigned to a con dence interval that locates how well it estimates the population mean. Ex 1: estimate weights of women at elon. 3) (100 lbs, 200 lbs) < best estimate . You generally want to be between 90% and 99% to provide a good and strong con dence interval. Fact 1: as con dence level increases, the width of the interval increases, so the margin of error also increases. As con dence level decreases, the width of the interval decreases, margin of error decreases.
