A contentbird customer writes:

Hello dear contentbird team, I have a question about WDF*IDF analysis. Could you explain why different tools give very different results for a WDF*IDF analysis? I compared your results in the text editor with the tool from Ryte and the free http://www.wdfidf-tool.com/ and was quite surprised. Is there an explanation for this?

The answer is relatively simple:

Each tool works "differently" - There is not THE one calculation, but the interpretation of the WDF/IDF "formula" is always different.

This already starts with the mathematical formula itself, which can be interpreted differently and continues with the document corpus, which is always different. Then there are points such as the different treatment of stop words, as well as the determination of the database and the results do not all look the same.

It is not the case that all tools do the same, because then it would not make sense to sell a paid tool with more extensive and "better" calculations, if there are also free variants.