Some historical trends are summarized below. The years in the table below represents the year the appointment would begin, e.g. 2015 for the 2014-2015 cycle.
The data aren't very clean, and the categorization of certain positions isn't always clear, especially in early years. Certain types of positions were also not consistently included in the rumor mill in previous years. So, in short, don't take these numbers too seriously.
The numbers below only include US positions, as non-US positions have been inconsistently included over the years.
Please email hepexrumor [at] gmail [dot] com to provide more information or to suggest revised numbers.