Biostatistics #16 - Conclusions from this study - USMLE Forums
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#1
06-08-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269
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%.
 The above post was thanked by: docoftheworld (06-08-2011), fadi551 (04-13-2014), rseruy (12-08-2012)

#2
06-08-2011
 USMLE Forums Veteran Steps History: 1 + CS Posts: 204 Threads: 56 Thanked 41 Times in 36 Posts Reputation: 51

ummmm is it A?
 The above post was thanked by: bebix (06-08-2011)
#3
06-08-2011
 USMLE Forums Guru Steps History: Not yet Posts: 324 Threads: 70 Thanked 236 Times in 143 Posts Reputation: 246

Is it E?
2SD above and below the mean (27%)..
 The above post was thanked by: bebix (06-08-2011)

#4
06-08-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269

Quote:
 Originally Posted by bebix 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%.

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]
 The above post was thanked by: rulz (10-06-2011)
#5
06-08-2011
 USMLE Forums Veteran Steps History: 1 + CS Posts: 204 Threads: 56 Thanked 41 Times in 36 Posts Reputation: 51

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 ...

#6
06-08-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269

Quote:
 Originally Posted by docoftheworld 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

Systolic blood pressure and confidence interval

 Tags Biostatistics-Epidemiology, Step-1-Questions

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