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#1
06-04-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269
Biostatistics #10 - Normal curve 2

Both mean and median of the diastolic blood pressure distribution of men aged 30 to 69 y/o are approximately 83 mmHg, and the standard desviation is 12 mmHg. These indices enable us to deduce each of the following statements except:

A) Approximately 68% of the men have diatolic blood pressure between 71 and 95 mmHg
B) The distribution is nearly symmetrical
C) The 95% confidence limits on the mean for all men, aged 30 to 69, in this population are 59 and 107 mmHg
D) Approximately half of the men have diastolic blood pressures over 83 mm Hg
E) The mean is not distorted very much by extremety high pressures in this case

Last edited by bebix; 06-05-2011 at 05:15 AM. Reason: men...thanks moe2185
 The above post was thanked by: Claus_CU (06-04-2011), struggle (06-05-2011)

#2
06-04-2011
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Quote:
 Originally Posted by bebix Both mean and median of the blood pressure distribution of men aged 30 to 69 y/o are approximately 83 mmHg, and the standard desviation is 12 mmHg. These indices enable us to deduce each of the following statements except: A) Approximately 68% of the men have diatolic blood pressure between 71 and 95 mmHg B) The distribution is nearly symmetrical C) The 95% confidence limits on the mean for all men, aged 30 to 69, in this population are 59 and 107 mmHg D) Approximately half of the mean have diastolic blood pressures over 83 mm Hg E) The mean is not distorted very much by extremety high pressures in this case
Is it D??? or E??
 The above post was thanked by: bebix (06-04-2011)
#3
06-04-2011
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E) The mean is not distorted very much by extremety high pressures in this case
 The above post was thanked by: bebix (06-04-2011)
#4
06-04-2011
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C) is incorrect

 The above post was thanked by: bebix (06-04-2011)
#5
06-04-2011
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@docoftheworld

 The above post was thanked by: docoftheworld (06-04-2011)
#6
06-04-2011
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#7
06-04-2011
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 The above post was thanked by: bebix (06-04-2011)
#8
06-04-2011
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I DONT KNOW!!!
#9
06-05-2011
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The answer I believe is E. You cannot infer anything about how mean is affected by certain values unless you have specific numbers to work with, such as population size and individual BP readings to sift through. Or perhaps another study that was conducted on the same parameters to compare with.

Choice D however I am pretty sure has a spelling mistake with the word "mean", I think it should read

D) Approximately half of the MEN have diastolic blood pressures over 83 mm Hg
#10
06-05-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,259 Times in 881 Posts Reputation: 3269

A) Approximately 68% of the men have diatolic blood pressure between 71 and 95 mmHg = TRUE (mean - 1 SD / mean + 1 SD)

B) The distribution is nearly symmetrical = TRUE (mean & median are 83)

C) The 95% confidence limits on the mean for all men, aged 30 to 69, in this population are 59 and 107 mmHg = FALSE (here is just mean + or - 2 SD, which is NOT the same as 95% CI)

D) Approximately half of the men have diastolic blood pressures over 83 mm Hg = TRUE (since mean & median are the same = normal/gaussian curve = MEDIAN the 50th percentile)

E) The mean is not distorted very much by extremety high pressures in this case = TRUE (because again, mean & median are the same. Otherwise, mean would be GREATER than median )
 The above post was thanked by: docoftheworld (06-05-2011), JBerger (06-05-2011), pass7 (06-05-2011), struggle (06-05-2011)
#11
06-18-2011
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confidence limit???

Quote:
 Originally Posted by bebix A) Approximately 68% of the men have diatolic blood pressure between 71 and 95 mmHg = TRUE (mean - 1 SD / mean + 1 SD) B) The distribution is nearly symmetrical = TRUE (mean & median are 83) C) The 95% confidence limits on the mean for all men, aged 30 to 69, in this population are 59 and 107 mmHg = FALSE (here is just mean + or - 2 SD, which is NOT the same as 95% CI) D) Approximately half of the men have diastolic blood pressures over 83 mm Hg = TRUE (since mean & median are the same = normal/gaussian curve = MEDIAN the 50th percentile) E) The mean is not distorted very much by extremety high pressures in this case = TRUE (because again, mean & median are the same. Otherwise, mean would be GREATER than median )

then what is the difference between confidence limit and confidence interval...i am sorry i dint understand...very poor in biostatistics
#12
06-18-2011
 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 winner21 then what is the difference between confidence limit and confidence interval...i am sorry i dint understand...very poor in biostatistics
The confidence level sets the boundaries of a confidence interval, this is conventionally set at 95% to coincide with the 5% convention of statistical significance in hypothesis testing. In some studies wider or narrower confidence intervals will be required. This rather depends upon the nature of the study.
The confidence interval is the range Q-X to Q+Y where Q is the value that is central to the study question (mean, OR, RR...), Q-X is the lower confidence limit and Q+Y is the upper confidence limit.

http://www.medicine.ox.ac.uk/bandoli...Conf_Inter.pdf
#13
06-18-2011
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bebix, nice biostats qns, Im planning on working on them...
Where did you get these from? Just making sure not NBME
#14
06-19-2011
 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 step1saga bebix, nice biostats qns, Im planning on working on them... Where did you get these from? Just making sure not NBME
Not NBME!

 Tags Biostatistics-Epidemiology, Step-1-Questions

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