You will encounter many types of articles and it is important to distinguish between these different categories of scholarly literature. Keep in mind the following definitions.
Peer-reviewed (or refereed): Refers to articles that have undergone a rigorous review process, often including revisions to the original manuscript, by peers in their discipline, before publication in a scholarly journal. This can include empirical studies, review articles, meta-analyses among others.
Empirical study (or primary article): An empirical study is one that aims to gain new knowledge on a topic through direct or indirect observation and research. These include quantitative or qualitative data and analysis. In science, an empirical article will often include the following sections: Introduction, Methods, Results, and Discussion.
Review article: In the scientific literature, this is a type of article that provides a synthesis of existing research on a particular topic. These are useful when you want to get an idea of a body of research that you are not yet familiar with. It differs from a systematic review in that it does not aim to capture ALL of the research on a particular topic.
Systematic review: This is a methodical and thorough literature review focused on a particular research question. It's aim is to identify and synthesize all of the scholarly research on a particular topic in an unbiased, reproducible way to provide evidence for practice and policy-making. It may involve a meta-analysis (see below).
Meta-analysis: This is a type of research study that combines or contrasts data from different independent studies in a new analysis in order to strengthen the understanding of a particular topic. There are many methods, some complex, applied to performing this type of analysis.
For some research projects you may be required to use primary sources. How can you identify these?
A primary source provides direct or firsthand evidence about an event, object, person, or work of art. Primary sources include historical and legal documents, eyewitness accounts, results of experiments, statistical data, pieces of creative writing, audio and video recordings, speeches, and art objects. Interviews, surveys, fieldwork, and Internet communications via email, blogs, listservs, and newsgroups are also primary sources. In the natural and social sciences, primary sources are often empirical studies—research where an experiment was performed or a direct observation was made. The results of empirical studies are typically found in scholarly articles or papers delivered at conferences.
Secondary sources describe, discuss, interpret, comment upon, analyze, evaluate, summarize, and process primary sources. Secondary source materials can be articles in newspapers or popular magazines, book or movie reviews, or articles found in scholarly journals that discuss or evaluate someone else's original research.