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Old 06-08-2011
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Stats Biostatistics #16 - Conclusions from this study

In a random sample of 500 school children in Baltimore, 27% are found to be susceptible to measles. The standard error of the percentage susceptible is 2%. From this it is correct to conclude that?

a. The probability is 95% that the percentage susceptible for all schoolchildren in Baltimore is between 25% and 29%.
b. The sample is biased.
c. Twenty-five of the children in the random sample were misclassified.
d. The data should be age adjusted.
e. The probability is 95% that the percentage susceptible for all schoolchildren in Baltimore is between 23% and 31%.
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ummmm is it A?
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Is it E?
2SD above and below the mean (27%)..
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Correct Answer correct answer

Quote:
Originally Posted by bebix View Post
In a random sample of 500 school children in Baltimore, 27% are found to be susceptible to measles. The standard error of the percentage susceptible is 2%. From this it is correct to conclude that?

e. The probability is 95% that the percentage susceptible for all schoolchildren in Baltimore is between 23% and 31%.
The correct answer is E)

Why not a)?

because, a 95% CI follows this formula:

"parameter" + or -[ Z_score x SE ]
In this case:

parameter = 27%
SE = 2%
Z_score = 1.96 (aprox. 2)

95% CI =

27 + or - [ 2 x 2 ] = [ 23, 31]
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standard error of the percentage susceptible is 2%."""

the concept that i understand is that there is skepticism about the true place of the mean that oscillates in a +- 2% range!!!

we have statistical certainty (which is only 95% from the utopian 100percent certainty) that this (percentage of susceptible children) will belong to the world of Mean+-SEM ...

Please correct me bebix
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Quote:
Originally Posted by docoftheworld View Post
standard error of the percentage susceptible is 2%."""

the concept that i understand is that there is skepticism about the true place of the mean that oscillates in a +- 2% range!!!

we have statistical certainty (which is only 95% from the utopian 100percent certainty) that this (percentage of susceptible children) will belong to the world of Mean+-SEM ...

Please correct me bebix
Dear docoftheworld:

When we are talking about X%CI, the only thing that we are saying is:
-We are 95% confident (or there is a 95% certainty) that the interval contains the "true" parameter (e.g. population mean)
-We are 95% confident that the true parameter is between [lower bound] and [upper bound]

and the classic formula is mean (or proportion, OR, RR...) plus or minus the product of the Z_score (type I error = 5% = Z_score two sided of 1.96 - 2.5% lower tail and 2.5% upper tail) times the SE

Please check this other post:
Systolic blood pressure and confidence interval
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