Updating systematic reviews
We examined the effects of regular updating of a systematic review of nicotine replacement therapy for smoking cessation. First, we assessed the effect of adding new data to meta-analyses, comparing results in 2000 with the results in 1994.Second, we assessed qualitatively the ways inwhich the nature of the questions addressed by the review had changed between the two dates.
Further placebo controlled NRT trials are not likely to add to the evidence base.
It is questionable whether updating the meta-analyses to include them is worthwhile.
The content of the systematic review has, however, changed, with the addition of data addressing questions not considered in the original review.
There is a tension between the principle of identifying the important questions prior to conducting a review, and keeping the review up to date as primary research identifies new avenues of enquiry.
There have been over 90 trials of nicotine replacement therapy for helping people to stop smoking.