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2.3 Sample Size Needed for Estimating Proportion STAT 506 - Sampling Theory and Methods

2.3 Sample Size Needed for Estimating Proportion STAT 506 - Sampling Theory and Methods

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STAT 506 - Sampling Theory and Methods ANGEL Department of Statistics Eberly College of Science Home // Lesson 2: Confidence Intervals and Sample Size 2.3 Sample Size Needed for Estimating Proportion Submitted by gfj100 on Mon, 11/30/2009 - 18:34 Unit Summary Sample size needed for estimating proportion Educated guess Conservative estimates Sample Size for Estimating Proportion Using the formula to find sample size for estimating the mean we have: Now, substitutes in and we get: When the finite population correction can be ignored, the formula is: Now, for finding sample sizes for proportion, in addition to using an educated guess to estimate p , we can also find a conservative sample size which can guarantee the margin of error is short enough at a specified α .

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A. Educated guess ( estimate p by ) : Note, may be different from the true proportion. The sample size may not be large enough for some cases, (i.e., the margin of error not as small as specified). B. Conservative sample size: Since p (1 - p ) attains maximum at p = 1/2, a conservative estimate for sample size is: Example
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2.3 Sample Size Needed for Estimating Proportion STAT 506 - Sampling Theory and Methods

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