What ratio of PhD graduates in STEM fields ultimately end up as (tenured) professors?
It's a shiny info-gram, but I think there is a lot wrong with it:


It transports the (common) misconception that the 53% leaving to industry after their PhD are sort of failed professors. At least in CS, and probably a lot of other STEM fields as well, many PhD students start with the full intention of leaving academia sometime. Hence, the better question the diagram should be asking is How many of those that want to become professors actually do?. Basically, I could come up with similar low percentages for every field. Let's say less than 1% of all working population of a city works in supermarkets. Does that mean that supermarket jobs are horribly hard to break into? No, because most people do not have the career goal of working in a supermarket in the first place.
Similarly for the 17% non-university research. In CS, good industry labs (like the ones at IBM or Microsoft) are preferable options for many researchers, so they would not take a professorship even if offered.
As already stated by commenters above, the title professor means different things in different places. In Austria, for instance, many high school teachers are officially "professors" (tenured even), despite not having a PhD or ever doing research. In Great Britain, very few people are professors (most are lecturers or senior lecturers). In Madrid I know an academic research lab (not affiliated with a university) that calls their staff members research professors. Job titles are almost never clear-cut.


That being said, I do think that there is a problem. If we assume a reasonably stable system (number of professors in a discipline stays more or less constant), then every tenured professor is in average allowed to see one of her/his students through to also become a tenured professor. Given that many tenured professors (at least here in Europe) maintain groups of 15+ PhD students at a time, I is pretty obvious even without digging into the data too much that the job market for professors is insanely competitive (which, incidentally, captures my personal experience hunting for tenure-track positions pretty well).