Explanation (tl;dr):
In this study, author is showing what is the difference between just balance and importance based harvesting. Technically importance is calculated on the account activity base (so transactions with over 1000 XEM). The result from this particular study says that actual NEM algorithm (PoI) is not much different if there wouldn't be this "importance" part in it, and harvesting probability would be similar in both cases. So the most probability of harvesting a block is comming from a "balance" parameter, not exactly from "importance" parameter.
good compendium from this https://docs.google.com/document/d/13M3wbdjI0Nzx-OKAd0dRCfOYFA_oT9Ydg96DkiUBsDs/edit?usp=sharing
There is also referred to a sheet
https://docs.google.com/spreadsheets/d/1LMLgretbB0EsRc8rAnvZQm_PEhtTeMqcku-VlN6iBTM/edit?usp=sharing
where one can compute his/hers own statistics. Maybe someone can find more positive results...