When doing nursing research, there are generally three categories that articles will fit under:
Primary or empirical research, secondary or review research, and a third category, comprising of both primary and secondary research. The third category is rarely, if ever, allowed as sources for nursing assignments. This category also includes student papers, like a dissertation or thesis.
IN GENERAL, your assignments will require you to find SPECIFIC types of primary and secondary sources. Be sure to read your assignment instructions very carefully to determine which sources to include.
Image from NCSU.