Editing Epidemiological method (section)

==Outline of the process of an epidemiological study==
# Establish that a problem exists
#* Full epidemiological studies are expensive and laborious undertakings. Before any study is started, a case must be made for the importance of the research.
# Confirm the homogeneity of the events
#* Any conclusions drawn from inhomogeneous cases will be suspicious. All events or occurrences of the disease must be true cases of the disease.
# Collect all the events
#* It is important to collect as much information as possible about each event in order to inspect a large number of possible risk factors. The events may be collected from varied methods of [[Epidemiology#Types of studies|epidemiological study]] or from censuses or hospital records.
#* The events can be characterized by [[incidence (epidemiology)|Incidence]] rates and [[prevalence]] rates.
#* Often, occurrence of a single disease entity is set as an event.
#* Given inherent [[Homogeneity and heterogeneity|heterogeneous]] nature of any given disease (i.e., the unique disease principle<ref name="pmid23307060">{{cite journal | vauthors = Ogino S, Lochhead P, Chan AT, Nishihara R, Cho E, Wolpin BM, Meyerhardt JA, Meissner A, Schernhammer ES, Fuchs CS, Giovannucci E | title = Molecular pathological epidemiology of epigenetics: emerging integrative science to analyze environment, host, and disease | journal = Modern Pathology | volume = 26 | issue = 4 | pages = 465–84 | date = April 2013 | pmid = 23307060 | pmc = 3637979 | doi = 10.1038/modpathol.2012.214 }}</ref>), a single disease entity may be treated as disease subtypes.<ref name="pmid20949563">{{cite journal | vauthors = Begg CB | title = A strategy for distinguishing optimal cancer subtypes | journal = International Journal of Cancer | volume = 129 | issue = 4 | pages = 931–7 | date = August 2011 | pmid = 20949563 | pmc = 3043163 | doi = 10.1002/ijc.25714 }}</ref> This framework is well conceptualized in the interdisciplinary field of [[molecular pathological epidemiology]] (MPE).<ref name="pmid20208016">{{cite journal | vauthors = Ogino S, Stampfer M | title = Lifestyle factors and microsatellite instability in colorectal cancer: the evolving field of molecular pathological epidemiology | journal = Journal of the National Cancer Institute | volume = 102 | issue = 6 | pages = 365–7 | date = March 2010 | pmid = 20208016 | pmc = 2841039 | doi = 10.1093/jnci/djq031 }}</ref><ref name="pmid21036793">{{cite journal | vauthors = Ogino S, Chan AT, Fuchs CS, Giovannucci E | title = Molecular pathological epidemiology of colorectal neoplasia: an emerging transdisciplinary and interdisciplinary field | journal = Gut | volume = 60 | issue = 3 | pages = 397–411 | date = March 2011 | pmid = 21036793 | pmc = 3040598 | doi = 10.1136/gut.2010.217182 }}</ref>
# Characterize the events as to epidemiological factors
## Predisposing factors
##* Non-environmental factors that increase the likelihood of getting a disease. Genetic history, age, and gender are examples.
## Enabling/disabling factors
##* Factors relating to the environment that either increase or decrease the likelihood of disease. Exercise and good diet are examples of disabling factors. A weakened immune system and poor nutrition are examples of enabling factors.
## Precipitation factors
##* This factor is the most important in that it identifies the source of exposure. It may be a germ, toxin or gene.
## Reinforcing factors
##* These are factors that compound the likelihood of getting a disease. They may include repeated exposure or excessive [[Stress (biology)|environmental stresses]].
# Look for patterns and trends
#* Here one looks for similarities in the cases which may identify major risk factors for contracting the disease. [[Outbreak#Types|Epidemic curves]] may be used to identify such risk factors.
# Formulate a hypothesis
#* If a trend has been observed in the cases, the researcher may postulate as to the nature of the relationship between the potential disease-causing agent and the disease.
# Test the hypothesis
#* Because epidemiological studies can rarely be conducted in a laboratory the results are often polluted by uncontrollable variations in the cases. This often makes the results difficult to interpret. Two methods have evolved to assess the strength of the relationship between the disease causing agent and the disease.
#* [[Koch's postulates]] were the first criteria developed for epidemiological relationships. Because they only work well for highly contagious bacteria and toxins, this method is largely out of favor.
#* [[Epidemiology#Bradford Hill criteria|Bradford-Hill Criteria]] are the current standards for epidemiological relationships. A relationship may fill all, some, or none of the criteria and still be true.
# Publish the results.<ref>{{cite book | last1 = Austin | first1 = Donald F. | last2 = Werner | first2 = S. Benson | name-list-style = vanc | title = Epidemiology for the health sciences: a primer on epidemiologic concepts and their uses | date = 1982 | publisher = Charles C. Thomas | location = Springfield, Ill. | isbn = 978-0-398-02949-4 | edition = 7th }}</ref>