While conducting a systematic review, publication bias could be determined using which of the following methods?
E. Publication bias refers to the tendency of journals to accept and publish certain types of studies more often than the others. In general, studies with results that are impressively significant or of higher quality by virtue of larger sample size are more successful in getting published. Publication bias can be considered as a form of selection bias when one attempts a systematic review or meta-analysis. Publication bias can be detected using a funnel plot – visual inspection of a graph drawn by plotting a measure of precision (often sample size) against treatment effect will reveal asymmetry of the two arms of the funnel-shaped graph if publication bias is present. Galbraith plot refers to a graph obtained by plotting a measure of precision such as (1/standard error) against standard normal deviate (log of odds ratio/standard error). The coordinates obtained from such a plot can be used to determine the extent of publication bias using linear regression. Failsafe N is another way of estimating publication bias. Consider a meta-analysis yielding a statistically significant difference in outcome between two interventions, despite suspected publication bias. Then failsafe N answers the question ‘How many missing studies are needed to reduce the effect to statistical non-significance?’ The higher the failsafe N, the lower the publication bias. If one could solicit and compare all unpublished data with published data, then publication bias would become obvious.
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In a RCT the randomization sequence is protected before and until the randomization is completed.
This is known as:
A. Allocation concealment refers to the process used to prevent fore knowledge of the assignment before allocation is complete. So the investigator who recruits subjects for a trial will not know the nature of assignment of consequent subjects that enter randomization. Allocation concealment seeks to prevent selection bias, protects the allocation sequence before and until assignment, and can almost always be successfully implemented in a RCT. It is often confused with blinding which seeks to prevent ascertainment bias and protects the sequence after allocation, and cannot always be implemented.
Data collected for a study on antidepressant efficacy show the outcome as observations of the number of days needed to achieve remission.
The standard deviation for such observations will be measured in which of the following units?
B. The standard deviation has the same units as the primary variable. This is an advantage of standard deviation compared with variance, which is also a measure of dispersion.
In a study presenting outcome in terms of median days of hospital admission, the collected data show many observations substantially higher than the median.
Which one of the following is correct regarding the above study?
D. If many observations are substantially higher than the median we can assume that the mean of the distribution might be greater than the median. This translates to a positively skewed distribution. No comments can be made on mode using the available information.
A trial is conducted to evaluate the efficacy of lamotrigine in patients with symptoms of recurrent depersonalization. While calculating the number of patients needed in the trial to demonstrate a meaningful effect, α level is set at 0.05.
Which of the following is true regarding alpha (α)?
C. α is the probability of type 1 error. It is used to set the threshold for statistical (not clinical) significance, often arbitrarily set as p = 0.01–0.05 (α = 1–5%). If α = 0.05, there is a 1 in 20 or 5% chance that the null hypothesis is rejected wrongly.
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