Glossary
Systematic review.
Direct answer
A systematic review answers a narrow question by searching, under a protocol written in advance, for every traceable study, selecting them against explicit criteria and appraising their quality. The whole procedure is published so that others can repeat it. That is what separates a systematic review from a narrative review citing literature at will.
The value of a review rests entirely on its search: querying a single database leaves out work published in other languages and other research traditions. Two independent people should screen titles and extract data. A review can be no better than the studies it includes, since pooling weak work does not manufacture a strong answer.
In equine research a systematic review often concludes that too few comparable studies exist. That empty answer is itself a finding: it shows where knowledge is missing instead of simulating a recommendation. Human medicine faces the opposite problem, where the sheer volume of publications is what makes selection difficult.
The evidence letter
Once a month: new syntheses, checked studies, and what has changed in the state of the evidence.