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#1




Interpreting this Case Control Study!
A casecontrol study is conducted to assess the risk for intussusception in infants under the age of 1 year who receive the rotavirus
vaccine. The medical records of all those who received the vaccine and those who did not receive the vaccine over a 6month period are reviewed. Results show 125 cases per 100,000 infantyears for infants who received the vaccine compared to 45 cases per 100,000 infantyears for infants who did not receive the vaccine. The investigators conclude that the relative risk for intussusception is 1.9 times greater in infants who receive the rotavirus vaccine (95% confidence interval of 0.5–7.7 and p=0.39). Which of the following is the most accurate interpretation of these results? A) The results do not show an association between rotavirus vaccine and intussusception, but they may be related B) The results show sufficient statistical power to identify an association between rotavirus vaccine and intussusception C) Rotavirus vaccine is associated with a 39% risk for intussusception D) Rotavirus vaccine causes intussusception in 1.9% of infants E) Rotavirus vaccine prevents 80 cases of intussusception per 100,000 infantyears 
#2




The answer is A.
btw, the investigators shouldn't report RR, because this is a case control and not a cohort...in any case, the "best" answer is A. 
#3




A) because the measure of association has a confidence interval that overlaps 1.
relative risks are reported in case control studies  they are inferred sometimes through measures such as incident density sampling, also relative risk approaches odds ratios at other times ( beyond the scope of usmle step 2 CK). Anyway hope this helps 
#4




Quote:

#5




Quote:
apologies if the thread is getting offtopic. 
#6




the answer is A)

#7




Quote:

#8




A
No association because:
1. CI 0.57.7 has the value "1" 2. p=0.39 
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benzo (06032011), usmle3evana (11272015) 
#9




Quote:
Yes. A indeed. Statistically not significant difference between two groups! Also ditto to mle guy. Thanks. This is an easy one because other statements don't make sense at all.
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docoftheworld (06012011) 
#10




what if we are given the CI only without p Value, and 1 wasnt within the CI, could we make inference without having the p? I had a question wherein everyone answered about the association (since CI doesnt include 1) although p wasnt presented, and one of the options was: we cant make inference based on given information (which i chose)
am i being too anal here? 
#11




Quote:
The same is true with this example: 95%RR[1.01, 1.02] 95%RR[5,7] In both cases the pvalue is less than 0.05, because the magic number 1 in not included...So there is an statistical association, but in case number one is VERY weak. 
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docoftheworld (06012011) 
#12




then whats use of including p value with CI then? if CI by itself is significant provided it doesnt include 1?

#13




Quote:
For example, in the bmj, they "don't like" pvalues that much... this is a clasical articule: pvalue bmj.pdf 
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healer2b (06012011) 
#14




so are we saying here that a combination of CI that includes 1 and p that is less than 0.05 is impossible? (and vice versa; a CI that doesnt include 1 CANNOT have a p more than 0.05

#15




Quote:
X%CI for difference between mean or proportions = in the number 0 is included, the pvalue MUST be above the preset alpha value 
The above post was thanked by:  
benzo (06032011), docoftheworld (06012011) 
#16




awesome bebix ... you rock

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BiostatisticsEpidemiology, Step2Questions 
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