USMLE step 1 : Q 32-34 :Answers

Question Number 32

Correct Answer: A

Explanation:
Recall bias is especially important when the investigator has to rely on patient recollection to establish risk factors. The authors used in this study are relying on recalled age of menstruation. An eighty year old is much less likely to accurately remember the age of her first menstruation than a thirty year old. It is also well known that people with a disease are likely to recall an exposure to a risk factor differently than someone without it and that knowledge of the purpose of the investigation may lead the patient. This is another example of recall bias.

 

Question Number 33

Correct Answer: C

Explanation:
This study demonstrates overestimation of survival duration among screen-detected cases (relative to those detected by signs and symptoms) when survival is measured from diagnosis. This is an example of Lead-time bias The apparent effects of early diagnosis and intervention (measured in terms of how screening-detected cases compare with cases detected by signs and symptoms) are always more favorable than the real effects (measured in terms of how a population that is screened compares with a population that is not). The comparison between screening-detected cases and others overestimates benefit because the former consists of cases that were diagnosed earlier, progress more slowly, and may never become clinically relevant. This comparison, therefore, is said to be biased. In the figure below (representing one patient), the patient survives for 10 years after clinical diagnosis and survives for 15 years after the screening-detected diagnosis. However, this simply reflects earlier diagnosis because the overall survival time of the patient is unchanged.

 

Question Number 34

Correct Answer: D

Explanation:
Journals tend to accept articles which show something which would be of interest to their readership. They want to be the first journal to report something new. Publication bias is another concern that is particularly germane to the meta-analytic process. It occurs when study results are differentially reported, depending on the direction and strength of their findings. Publication bias is not an uncommon phenomenon, and it appears that the failure to publish the results of a particular study actually lies more with the investigator than with the editor. Investigators acknowledge that they are less likely to pursue publication when they have obtained uninteresting results. Moreover, authors can also impose publication bias if they selectively exclude data from a publication based on the nature of the findings. Methods have been devised to estimate the size of the problem in a given analysis