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Ken Butler (30)
Lecture
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CHAPTER 19  CONFIDENCE INTERVALS FOR PROPORTIONS
MAIN TEXT
WHO  Sea fans
WHAT  % infected
WHEN  June 2000
WHERE  Las Redes Reef, Akumal, Mexico (40 ft deep)
WHY  Research
relevant info

n
= 104
 amt infected = 54/104
=>
= 51.9% = 0.519
 this is sample prop. for this particular random sample of sea fans that
were randomly collected from relevant loc.
 recall: sample prop's vary from one sample to another
CONFIDENCE INTERVAL
Known Information and Not Known
 we know:
 sample prop. retrieved from doing ONE SRS.
 we do not know:
p
 prop. of all infected sea fans on Las Redes Reef
 this is what we want to know
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 what else we know: sampling distribution of
is centred at
p
 SD of sampling distribution is given by:
Problem 2:
 do not know true standard deviation of sampling distribution model, b/c we do not
have
p
Only pages 13 are available for preview. Some parts have been intentionally blurred.
 instead, we find standard error (SE()): estimated SD of sampling distribution of the
sample statistic (in this context, the prop.)
 standard error is estimated SD for sampling distribution
(ex)
 for sea fans, it is:
 sampling model for
 what they did was show the ±1SE, ±2SE, ±3SE, using retrieved sample prop.
NOTATION ALERT

 samplebased estimate of true prop
p
 q is 1  p
 so qhat = 1 
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