When a topic is new to you and you need an overview of the topic, encyclopediae and textbooks are great at giving an overview or introduction.
For more detailed exploration of a topic, books provide the focus you want. UC Berkeley has millions of books!
For lab research, handbooks and lab protocols provide information on the materials and procedures for experimental work.
The next format type is journals. They report on the findings of current research studies, offering the most up-to-date and detailed information on a topic.
A single journal issue will have many articles, and each article is devoted to a research study. There is a standard pattern in how journal articles are written, and knowing this pattern will help you find the information you need:
Finally, databases are what you use to find journal articles. Databases let you search across many (often millions) of journal articles to find the papers relevant to your research topic.
What to consider when thinking about your research topic
Much current research in environmental health is interdisciplinary.
The terms you use when searching PubMed, Web of Science, or other databases may need to include concepts from different fields of science.
Is your topic researchable?
Effects of vehicular emissions from 1995 Toyotas on elderly women in Berkeley
Health effects of seasonal variation in PM2.5 levels in the San Francisco Bay Area
Air pollution in the United States
Information on chemicals/substances
Before you delve into the research literature on a topic, it can be helpful to get some basic information on the substance(s) of interest.
Let's talk about indexing!
Do you want articles on HIV (a virus) or articles on HIV diseases?
Do you want articles on nanofibers or articles on nanofibres?
Is lead a noun or a verb?
Indexing means a controlled vocabulary (a finite list of terms) is used to assign subject terms to articles.
Controlled vocabulary schemes are often hierarchical; any given term will have broader and (possibly) narrower terms. Example:
Subject terms tend to have a single, unambiguous definition. Example:
Subject terms may also be called thesaurus terms, descriptors, or (in PubMed) Medical Subject Headings (MeSH).
Evaluation is about determining the quality, value, or importance of something in order to take action. It is underpinned by the systematic collection of information and evidence.
What is evidence?
All research is (potentially) "evidence" and there are no "perfect" studies.
Critically evaluating what you read will help any unearth biases or methodological shortcomings that may be present
Is there an agenda (bias)?
It's doubtful that any study of humans is without some kind of bias, either in the study design, or in the author's pre-existing beliefs. How bias in methodology was controlled and the significance of bias in any particular study is what's relevant.
Things to consider:
This article (PDF) discusses the "manufactured uncertainty" created by industry groups that sponsor research and publishing on chemicals.
Is qualitative research "evidence"?
If your goal is to understand beliefs and meanings in the group with whom you are working, then qualitative studies can be important.
Reliability and validity
Reliable data collection: relatively free from "measurement error."
Is the survey written at a reading level too high for the people completing it?
If I measure something today, then measure it again tomorrow using the same scale, will it vary? Why?
Validity refers to how well a measure assesses what it claims to measure
If the survey is supposed to measure "quality of life," how is that concept defined? Is it measurable?
What to consider when looking at survey or estimated data:
Ten simple rules for writing a literature review.
Pautasso M. PLoS Comput Biol. 2013;9(7):e1003149. doi:10.1371/journal.pcbi.1003149
Conducting the Literature Search.
Chapter 4 of Chasan-Taber L. Writing Dissertation and Grant Proposals: Epidemiology, Preventive Medicine and Biostatistics. New York: Chapman and Hall/CRC, 2014.
A step-by-step guide to writing a research paper, from idea to full manuscript. Excellent and easy to follow blog post by Dr. Raul Pacheco-Vega.