Although reference works might seem comprehensive and concise summaries of information, even a rudimentary survey of their analysis of the primary sources demonstrates that this idealized view is naive. Catalogs frequently disagree for one of several reasons:

1. New catalogs add new material. This is seen intuitively as a positive development, implying that new catalogs build upon the labor of former ones and “discover” new relevant sources that mention plague outbreaks. However, reality is more complex since the added material does not necessary conform to the definition of a plague outbreak that earlier catalogs adopted. In other words, earlier catalogs may have been aware of a particular report and consciously chose not to include it in their catalog since it did not fit their definition of plague.
2. New catalogs remove old material. As in the previous point, a change in the definition of a plague outbreak would likely also remove some sources from consideration as plague outbreaks. Here again the earlier catalog is not necessarily wrong and such cases should be examined closely.  
3. Temporal and spatial differences. The primary sources rarely provide scholars with all the details they would like to have about a plague’s date and exact spatial scope. The strict format of catalogs forces scholars to fill in fields such as date or location, artificially reducing the amount of vagueness and conveying a clean version of the messy reality behind the primary source reference. The different interpretations scholars have of particular cases can result in major differences in both the spatial and temporal range of a plague case.  
4. Typos. Most plague catalogs were put together by single scholars or small groups, and as such are particularly sensitive to typos and random errors. Difficulties in peer-reviewing and accessing the many sources involved makes it hard to catch all these mistakes, and accordingly we encountered such issues in all plague catalogs we analyzed for the plague app.

 The plague app attempts to mitigate these issues as far as possible. By including all the known references to plague outbreaks in all three catalogs we avoid removal of old material (#2). The difficulties in diagnosing a past outbreak as plague or another disease led us to include additional cases of epidemics. We attempt to convey the certainty/seriousness of each outbreak through a particular statistic <link to certainty/seriousness>, which albeit subjective allows us to add more material yet also convey a more nuanced analysis of the material (#1). Allowing users to examine how the different catalogs analyze each primary source offers a workable solution to the temporal and spatial differences between them. By making these differences visible to users, yet also offering our own interpretation of the temporal and spatial scope of plague, we democratize the data and offer each user the opportunity to reach their individual conclusion through accessing all the information (#3). Finally, by publishing our app digitally and opening a feedback channel with users we can easily “catch” and fix typos and other minor issues almost instantly - unlike books that would have to wait for the next printing (if at all; #4).