Epidemiological method 1

Epidemiological methodThe science of epidemiology has matured significantly from the times of Hippocrates and John Snow. Thetechniques for gathering and analyzing epidemiological data vary depending on the type of disease being monitoredbut each study will have overarching similarities.

Outline of the process of an epidemiological study1.1. Establish that a problem exists

•• Full epidemiological studies are expensive and laborious undertakings. Before any study is started, a case mustbe made for the importance of the research.

2.2. 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.3.3. Collect all the events

• It is important to collect as much information as possible about each event in order to inspect a large number ofpossible risk factors. The events may be collected from varied methods of epidemiological study or fromcensuses or hospital records.

• The events can be characterized by Incidence rates and prevalence rates.4.4. Characterize the events as to epidemiological factors

1.1. Predisposing factors•• Non-environmental factors that increase the likelihood of getting a disease. Genetic history, age, and gender

are examples.2.2. Enabling/disabling factors

•• Factors relating to the environment that either increase or decrease the likelihood of disease. Exercise andgood diet are examples of disabling factors. A weakened immune system and poor nutrition are examples ofenabling factors.

3.3. Precipitation factors•• This factor is the most important in that it identifies the source of exposure. It may be a germ, toxin or gene.

4.4. Reinforcing factors•• These are factors that compound the likelihood of getting a disease. They may include repeated exposure or

excessive environmental stresses.5.5. Look for patterns and trends

• Here one looks for similarities in the cases which may identify major risk factors for contracting the disease.Epidemic curves may be used to identify such risk factors.

6.6. 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.7.7. Test the hypothesis

•• Because epidemiological studies can rarely be conducted in a laboratory the results are often polluted byuncontrollable variations in the cases. This often makes the results difficult to interpret. Two methods haveevolved 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 workwell for highly contagious bacteria and toxins, this method is largely out of favor.

Epidemiological method 2

• 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.

8. Publish the results[1]

MeasuresEpidemiologist are famous for their use of rates. Each measure serves to characterize the disease giving valuableinformation about contagiousness, incubation period, duration, and mortality of the disease.

Measures of occurrence1. Incidence measures

1. Incidence rate, where cases included are defined using a case definition2.2. Hazard rate3.3. Cumulative incidence

2. Prevalence measures1.1. Point prevalence2.2. Period prevalence

Measures of association1.1. Relative measures

1.1. Risk ratio2.2. Rate ratio3.3. Odds ratio4.4. Hazard ratio

2.2. Absolute measures1.1. Absolute risk reduction2.2. Attributable risk

1.1. Attributable risk in exposed2.2. Percent attributable risk3. Levin’s attributable risk

Other measures1. Virulence and Infectivity2. Mortality rate and Morbidity rate3.3. Case fatality4. Sensitivity (tests) and Specificity (tests)

External links• Epidemiologic.org [2] Epidemiologic Inquiry online weblog for epidemiology researchers• Epidemiology Forum [3] A discussion and forum community for epi analysis support and fostering questions,

debates, and collaborations in epidemiology• The Centre for Evidence Based Medicine [4] at Oxford maintains an on-line "Toolbox" of evidence based

medicine methods.• Epimonitor [5] has a comprehensive list of links to associations, agencies, bulletins, etc.• Epidemiology for the Uninitiated [6] On line text, with easy explanations.

Epidemiological method 3

• North Carolina Center for Public Health Preparedness Training [7] On line training classes for epidemiology andrelated topics.

• People's Epidemiology Library [8]

References[1][1] Austin, Donald F., and S. B. Werner. Epidemiology for the health sciences a primer on epidemiological concepts and their uses. Springfield,

Ill: C. C. Thomas, 1974. Print.[2] http:/ / www. Epidemiologic. org/[3] http:/ / www. epidemiologic. org/ forum/[4] http:/ / www. cebm. net/ toolbox. asp[5] http:/ / www. epimonitor. net/ index. htm[6] http:/ / bmj. bmjjournals. com/ epidem/ epid. html[7] http:/ / www. sph. unc. edu/ nccphp/ training/[8] http:/ / www. epidemiology. ch/ history/ betaversion. htm

Austin, Donald F., and S. B. Werner. Epidemiology for the health sciences a primer on epidemiologic concepts andtheir uses. Springfield, Ill: C. C. Thomas, 1974. Print.

Article Sources and Contributors 4

Article Sources and ContributorsEpidemiological method  Source: http://en.wikipedia.org/w/index.php?oldid=502425655  Contributors: Arcadian, Barticus88, Charles Matthews, Dcfleck, GenOrl, Gsociology, JeffreyN,Nono64, Oleg Alexandrov, Patiwat, SimonP, Tobycat, Wikid, Wmahan, 19 anonymous edits

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