# 32 - Because we don't know the value p we replace the...

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Because we don’t know the value p, we replace the standard deviation by the standard error of , to get the confidence interval . Draw an SRS of size  n  from a large  population  that contains an unknown  proportion  p  of successes. An approximate level C  confidence interval  for  p  is where  z * is the critical value for the standard Normal density curve with area C  between − z * and  z *. Use this interval only when the numbers of successes and failures in the sample  are both at least 10. ------n >10 and n(1- )>10 The margin of error in the large-sample confidence interval for p is Here  z * is the standard Normal critical value for the level of confidence we want.  Because the margin of error involves the sample proportion of successes  , we  need to guess this value when choosing  n . Call our guess  p *. Here are two ways  to get  p *: 1. Use a guess  p

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32 - Because we don't know the value p we replace the...

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