About PubMed by Year

Why PubMed by Year?

The biomedical literature is a not only a tool for finding the newest answers, but is also a record of what researchers and clinicians have concerned themselves with over the decades. PubMed now generates a graph showing reults by year for a search, but this may not show actual trends given that the astonishing increase of the biomedical literature over time makes a simple count less illustrative of changes for any given search.

For exmaple, here are graphs of raw counts for the searches 'Diabetes mellitus, type 2', 'Malaria' and '“Heart diseases[mesh]”':

All three show a steep increase, but it is hard to discern what this means given the background increase in items. However, if we compare those yearly totals to those for PubMed as a whole and lay them out on the same graph, a clearer picture of publication trends emerges:

How it works

PubMed does a thorough job of covering the vast biomedical literature, as it contains citations from around 26,000 journals published around the world. Within PubMed, the MEDLINE database provides thorough coverage of this literature from 1966 onwards and OLDMEDLINE take us back to 1946 for some parts of the literature. There are also a relative smattering of PubMed Central citations between the nineteenth century and the present.

Yearly counts for each search are taken from PubMed and compared to year-by-year totals. Hits per 100,000 by year are calculated by the following formula:

\[ {\text{Number of search results that year} \over \text{Total number of PubMed results that year} } \times 100000.\]

Caveats

When you enter a search into the search bar, you are searching PubMed directly, meaning that your search is parsed by NCBI's automatic term mapping algorithm. If something doesn't make sense, you can try your search in a new PubMed window (or click any year on the graph) and examine the "Details" from the Advanced Search Builder page.

Use caution when interpreting the results of a Medical Subject Heading search, as older records are not typically re-indexed after a new heading is added to the thesaurus.