Analysis of marketing activities of American self-publishers

How can the development of the US book market and especially the self-publishing market be explained? Let's take a look at the marketing strategies of American self publishers. A survey of almost 8000 self-publishing authors serves as a basis (source: Bookbaby). What promotional measures do they use or initiate themselves to market their books?

Successful self-publishing authors use a bundle of marketing measures. These range from pre-sales promotions to book parties to readings in bookstores. The average US author uses 3.5 marketing efforts to boost sales of their book. The most successful authors, i.e. those who were able to earn more than 5000 dollars with their last book project, even used 5.3 measures. Authors with earnings of less than 100 dollars only came up with 2.2 measures. So the more they invest in marketing their book, the greater their sales success.

As the graphic is in German, I translated it:

Does this coincide with your experience?