 Each of these authors used different approaches to arrive at their categories. Popa 2004 and Trifonov 2011 attempted to reverse engineer the categories from dozens of definitions collected from many dozens of experts, while Malaterre and Chartier 2019 conducted a more extensive, text-mining approach across 30,000 scientific articles selected from journals that published pieces in biology. As one can see, there are areas of rough overlap, but each categorization scheme has its own unique categories as well.