Margin of Error

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Information about Margin of Error
Education

Published on October 27, 2008

Author: headlessprofessor

Source: authorstream.com

Margin of Error : Margin of Error & Confidence Intervals headlessprofessor When this applies : When this applies A sample is being used to estimate a population mean What it tells you : What it tells you How far off your estimate is likely to be What you need : What you need Sample size = N What you need : What you need Sample size = N Sample mean What you need : What you need Sample mean & N Standard deviation What you need : What you need Sample mean & N Standard deviation Z score for level of confidence What you need : What you need Sample mean & N Standard deviation Z score for level of confidence (z = 1.96) How to Calculate : How to Calculate Standard Deviation Divided by Square Root Of Sample Size How to Calculate : How to Calculate Standard Deviation Divided by Square Root Of Sample Size (standard error) How to Calculate : How to Calculate Margin of Error = Standard Error times Z score Example : Example N = 49 Mean = 78 Std Dev = 5 Z score = 1.96 How to Calculate : How to Calculate Square root of sample size = Square root of 49 = 7 How to Calculate : How to Calculate Standard deviation divided by square root of sample size 5 / 7 How to Calculate : How to Calculate Standard deviation divided by square root of sample size 5 / 7 = 0.714 How to Calculate : How to Calculate Standard deviation divided by square root of sample size 5 / 7 = 0.714 Standard Error How to Calculate : How to Calculate Standard deviation divided by square root of sample size 5 / 7 = 0.714 Standard Error How to Calculate : How to Calculate Margin of Error = Std Error X Z 0.714 X 1.96 How to Calculate : How to Calculate Margin of Error = Std Error X Z 0.714 X 1.96 = 1.40 What this means : What this means Margin of Error: 95% of the time, the population mean will be within 1.40 of the mean Confidence Interval : Confidence Interval The range of scores from mean – ME to mean + ME Example of Confidence Interval : Example of Confidence Interval The range of scores from 78 – 1.40 to 78 + 1.40 Example of Confidence Interval : Example of Confidence Interval The range of scores from – 1.40 to 78 + 1.40 76.6 to 79.4 To get narrower : To get narrower Have a lower standard deviation To get narrower : To get narrower Have a lower standard deviation Accept a lower level of confidence (e.g., .90 instead of .95) To get narrower : To get narrower Have a lower standard deviation Accept a lower level of confidence (e.g., .90 instead of .95) Use a larger sample size N To get a better level of confidence : To get a better level of confidence Have a lower standard deviation To get a better level of confidence : To get a better level of confidence Have a lower standard deviation Accept a broader confidence interval To get a better level of confidence : To get a better level of confidence Have a lower standard deviation Accept a broader confidence interval Use a larger sample size Use T instead of Z : Use T instead of Z When population SD is not known Use T instead of Z : Use T instead of Z When population SD is not known Use df = N - 1 Margin of Error : Margin of Error & Confidence Intervals headlessprofessor

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