Do use the PubMed Clinical Queries? If so, you should be aware that the “Broad” scope may not be as broad as one would like. Instead, there are many occasions when items that appear in a “Narrow” scoped search just don’t show up in their Broad counterpart. This is particularly true for Prognosis, where a searcher could easily miss one (presumably relevant) Prognosis/Narrow citation for every ten Prognosis/Broad citations retrieved.
Much more detail can be found in my new article, published in the most recent issue of JMLA:
Sperr, Edwin Vincent Jr. “Mind the gap: identifying what is missed when searching only the broad scope with clinical queries.” Journal of the Medical Library Association : JMLA vol. 107,3 (2019): 333-340. doi:10.5195/jmla.2019.589