When your assignments ask you to find primary research studies, this simply means that you are looking for original research. Do not confuse primary research studies with primary sources.
Unlike primary sources, primary research studies will cite other studies. In order to do effective and valid research, scientists must evaluate current research to see what conclusions can be drawn and what gaps there are to fill with additional research. This research is usually reported in the introduction/overview or literature review section at the beginning of the article or report.
While there is no fool-proof formula for identifying primary research studies, there are some clues you can look for.
Typically, the abstract will contain a brief summary of the paper. It should include essential points or findings and may include methods and results. Sometimes scanning the abstract will give you enough information to be able to tell if research performed by the authors is being described. The condensed information may be too difficult for you to interpret right away, though, so you will need to move on to the rest of the paper.
You should see a section that says, "Methods" or "Materials and Methods."
In this section, you should be able to find the answers to the simple questions:
If you can answer all these questions, it is typically a primary research study.
One exception will be case studies/reports. Case studies/reports are not required to include a methods section, but are still considered a primary research study.
Another exception will be systematic reviews and meta-analyses. These are research studies that include a methods section, but, because they are using secondary data (other researchers' studies), they are not primary research studies.
Look for a section that tells you the results of the research the authors did in the methods section. If this section is too complex, look for a subsequent section that discusses the results. If you do not see a section that informs you of the outcome of the authors' research, then this is a big clue that this is not a primary research study.
Tables and Figures
Lastly, scan the tables and figures that seem to be displaying the results of the research study performed. If citations are given for these tables or figures, then they are not the results of a study being reported in the article you looking at but most likely the results of primary research studies being reviewed by the authors.
A simple rule of thumb for identifying secondary literature is that the authors of the article did not perform the research being described.
This type of literature includes reviews (such as systematic reviews and meta-analyses), clinical practice guidelines, and evidence summaries.
Some journals will make secondary literature easy to identify by actually printing, "Review" or "Review Article" on the first page.