Chemistry

In the Sciences, secondary sources are equal to review articles.

Secondary Sources in the Sciences: 

• Literature reviews, systematic reviews, meta-analyses
• Publications about the significance of research or experiments
• Review of the results of several experiments or trials i.e. review articles 
• Analysis of a clinical trial
• Letters to the editor, editorials, perspectives, etc.

Note that meta-analyses, systematic reviews, or literature reviews may have a "Methods" section too. However, the methods will indicate that the authors have searched particular databases on a topic and then analyzed the results or have evaluated the important research articles on a topic. 

This is a review article based on the following criteria: 

• Title includes "comparisons"
• Abstracts states "systematic review"
• Phrases such as "publications with comparisons" and "accumulation of clinical data"