Dear Antonia,
I was unfortunate enough to buy the so-called "frequency dictionary" by K. Schmidt a few years ago.
Having checked it, I was astounded by the number of mistakes. I actually wanted to write an (outraged)
book review, and here is a good place to warn everyone that the amount and character of mistakes
definitely render the book unsuitable for learning purposes, or, put simply, any learner should avoid it.
However, those who have already learnt the language and read the core texts, would find the arrangement
of lexical items from the most frequent ones to the least frequent ones at least probable (only regarding the
Sutta-piṭaka texts).
I also couldn't find the original publication and I wonder if the publishers of the book perhaps
got their hands on an unpublished draft/manuscript or simply put the name of the author on someone's/
their own creation for respectability.
In principle, some of the most frequent Pāli words are those which comprise the most popular formulas, verbatim
repeated portions of texts. The full statistical analysis, AFAIK, has not been done, but some of the materials
published by the Pāli Text Society provide valuable information in this regard.
Another important question is what we understand by "Pāli". The four old Nikāyas, the whole Sutta-piṭaka, the whole Tipiṭaka,
the commentaries, the subcommentaries, the learned treatises like the Visuddhimagga or the modern Pāli works?
Different people are interested in different "layers" of the Pāli literature, and for someone who is interested in later
(for instance, medieval) Pāli sources a list of the most frequent words of the four old Nikāyas would be of little use.
Kind regards,
Gleb Sharygin