Definitions of what is primary or secondary differs across the disciplines. For the sciences, this is how we would define the different types of sources:

Primary source literature in the sciences:

• documents the results of original research
• is written by those who have conducted the research
• includes firsthand information about their methodologies, data, results, or conclusions.

Secondary source literature in the sciences:

• summarizes, compares, critiques, or interprets the primary literature.

Tertiary sources in the sciences:

• are collections of primary and/or secondary sources

Characteristics of primary sources in the sciences include:

• Report original research, ideas, or scientific discoveries for the first time
• Report results/findings/data from experiments or research studies
• May also be referred to as primary research, primary articles, or research studies
• DO NOT include meta-analyses, systematic reviews, or literature reviews - these are secondary sources
• Are frequently found in peer-reviewed or scholarly journals
• Should explain the research methodology used (randomized controlled trial, etc)
• Frequently include methods, results, and discussion sections
• Are factual, not interpretive