WebAIM have published the results of their 2017 survey of screen reader use. You can read the full report at https://webaim.org/projects/screenreadersurvey7/.
In addition to containing a mass of interesting information on screen reader use the WebAIM survey is valuable because it is the latest in a series stretching back to 2009 so that you can see how screen reader use has changed over time. However the responses to the survey are heavily biased towards North America and be aware that for other parts of the world small sample size may present misleading results. Despite that warning the survey is fascinating reading for those with an interest in assistive technology.
Two findings will catch the eye of website accessibility campaigners, compared to the last survey in 2015 positive perceptions of the state of web accessibility have risen slightly, while a large majority believe that the answer to Which of the following do you think would have a bigger impact on improvements to web accessibility? is better websites, not better assistive technology.