Age, race, gender, religion, etc. are items included in the study of

The answer is demographics as this is responsible for providing statistical data with the contents about the population or groups, studying it has contents of the following such as—age, gender, religion, race and other things that will describe the group or individual that will be of help with the study.

answer; not notated (at least, not in the traditional sense) and includes many improvised sections and solos;