BR_Lec 20 & 21

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[email protected] Lecture - 20 Syed Far Abid Hossain Determining the Size of a Sample
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BR_Lec 20 & 21

Transcript of BR_Lec 20 & 21

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    Lecture - 20Syed Far Abid HossainDetermining the Size of a Sample

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  • Sample [email protected] accuracy: refers to how close a random samples statistic (sign) is to the true populations value it representsSample size is related to accuracy

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  • How to Interpret Sample [email protected] a reportThe sample is accurate 7% at the 95% level of confidenceFrom a news articleThe accuracy of this survey is 7%

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  • How to Interpret Sample [email protected] Finding: 60% are aware of our brandSo between 53% (60%-7%) and 67% (60%+7%) of the entire population is aware of our brand

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  • [email protected] is only one method of determining sample size that allows the researcher to PREDETERMINE the accuracy of the sample resultsThe Confidence Interval Method of Determining Sample Size

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  • The Confidence Interval Method of Determining Sample [email protected] method is based upon the Confidence Interval and the Central Limit TheoremConfidence interval: range whose endpoints define a certain percentage of the response to a question

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  • Review: What does sample accuracy [email protected] size of 1,000Finding: 40% of respondents like our brandSample accuracy is 3% (via our formula)

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  • Sample Size [email protected], statisticians have given us a formula which is based upon these relationships.The formula requires that weSpecify the amount of confidence we wish (95%)Estimate the variance in the populationSpecify the amount of desired accuracy we want.When we specify the above, the formula tells us what sample we need to use

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  • [email protected]***What is Sample Accuracy? How to Interpret Sample Accuracy? Give an example assuming 95% confidence level.

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  • Lecture 21Syed Far Abid HossainSample Size [email protected]

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  • Sample Size [email protected] sample size formula for estimating a percentage:

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  • Estimating a Percentage: What is [email protected]=1.96 (95% confidence)p=42q=100-p=58e=5What is n?

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  • Special Sample Size Determination [email protected] from small populations:Small population: sample exceeds 5% of total population size

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  • Special Sample Size Determination [email protected] size using nonprobability sampling:When using nonprobability sampling, sample size is unrelated to accuracy, so cost-benefit considerations must be used.

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  • Practice [email protected] Using the formula provided in your text, determine the approximate sample sizes for each of the following cases, all with precision (allowable error) of 5%:Variability of 30%, confidence level of 95%

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  • Practice [email protected] Using the formula provided in your text, determine the approximate sample sizes for each of the following cases, all with precision (allowable error) of 5%:Variability of 60%, confidence level of 99%

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  • Practice [email protected] Using the formula provided in your text, determine the approximate sample sizes for each of the following cases, all with precision (allowable error) of 5%:Unknown variability, confidence level of 95%

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