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#1
05-26-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269
Systolic blood pressure and confidence interval

In a random sample of 30 patients from a small city, you have measured the systolic blood pressure (SBP). The 95% conﬁdence interval(CI) for the mean SBP is (122,138).
Which of the following statements gives a valid interpretation of this interval?

(a) About 95% of the sample of patiets have a SBP between 122 and 138.
(b) About 95% of the of the patients in that city have a SBP between 122 and 138.
(c) If the sampling procedure were repeated many times, then approximately 95% of the resulting CI would contain the mean SBP for patients in the city.
(d) If the sampling procedure were repeated many times, then approximately 95% of the sample means would be between 122 and 138.
(e) The probability that the sample mean falls between 122 and 138 is equal to 0.95.
 The above post was thanked by: apx85 (05-26-2011), Claus_CU (05-26-2011), prataptetali (05-27-2011), rseruy (12-08-2012), skido (05-27-2011), struggle (06-09-2011), usluipek (05-26-2011)

#2
05-26-2011
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(e) The probability that the sample mean falls between 122 and 138 is equal to 0.95.
 The above post was thanked by: bebix (05-26-2011)
#3
05-26-2011
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Quote:
 Originally Posted by donofitaly (e) The probability that the sample mean falls between 122 and 138 is equal to 0.95.
I also think that the right answer is E)
 The above post was thanked by: bebix (05-26-2011)
#4
05-26-2011
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I think it should be D, because CI is defined as a Range of values in which repeated means of sample expected to fall... So in order to get the option E i would likely to see option D to conclude with option E.

 The above post was thanked by: bebix (05-26-2011)
#5
05-26-2011
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i think its e
 The above post was thanked by: bebix (05-26-2011)
#6
05-26-2011
 USMLE Forums Addict Steps History: 1 + CS Posts: 113 Threads: 8 Thanked 88 Times in 61 Posts Reputation: 98

Quote:
 Originally Posted by bebix In a random sample of 30 patients from a small city, you have measured the systolic blood pressure (SBP). The 95% conﬁdence interval(CI) for the mean SBP is (122,138). Which of the following statements gives a valid interpretation of this interval? (a) About 95% of the sample of patiets have a SBP between 122 and 138. (b) About 95% of the of the patients in that city have a SBP between 122 and 138. (c) If the sampling procedure were repeated many times, then approximately 95% of the resulting CI would contain the mean SBP for patients in the city. (d) If the sampling procedure were repeated many times, then approximately 95% of the sample means would be between 122 and 138. (e) The probability that the sample mean falls between 122 and 138 is equal to 0.95.
I between c) & d)
 The above post was thanked by: bebix (05-26-2011)
#7
05-26-2011
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 557 Times in 318 Posts Reputation: 567

I think it's D.

95% CI does NOT equal 95% probability. It is a 95% confidence. It's a nitpicky thing in my opinion
 The above post was thanked by: bebix (05-26-2011)
#8
05-26-2011
 USMLE Forums Addict Steps History: 1 + CS Posts: 113 Threads: 8 Thanked 88 Times in 61 Posts Reputation: 98

just for diversity... I'll choose C)
 The above post was thanked by: bebix (05-26-2011)
#9
05-26-2011
 USMLE Forums Master Steps History: 1+CK+CS Posts: 1,039 Threads: 189 Thanked 557 Times in 318 Posts Reputation: 567
erratum ;)

I meant C I guess diversity was illusional
 The above post was thanked by: bebix (05-26-2011)
#10
05-26-2011
 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 Casandra I meant C I guess diversity was illusional
very good!

the correct answer is C) If the sampling procedure were repeated many times, then approximately 95% of the resulting CI would contain the mean SBP for patients in the city.

Any one interval from a particular sample may or may not contain the true parameter. In this case, 95% of such intervals that could be constructed from repeated random samples of size n contain the true parameter (in this case μ).

In other words:
-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 as Casandra said, 95% CI does not equal 95% probability.
 The above post was thanked by: Claus_CU (05-26-2011), donofitaly (05-27-2011), prataptetali (05-27-2011), rulz (05-26-2011), usluipek (05-26-2011)
#11
05-26-2011
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Very Good question, those were my real 2 answer,, Glad i was close... =) Keep it up....
 The above post was thanked by: bebix (05-26-2011)
#12
06-09-2011
 USMLE Forums Addict Steps History: 1 + CS Posts: 113 Threads: 8 Thanked 88 Times in 61 Posts Reputation: 98

do u have more questions like this one???
#13
06-09-2011
 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 Claus_CU do u have more questions like this one???
Tomorrow I'll post some more
 The above post was thanked by: carla (06-15-2013)

 Tags Biostatistics-Epidemiology, Step-1-Questions

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