View source for 20. Descriptive epidemiological studies, cross-sectional studies

* Descriptive studies
** These studies try to identify the relation between a disease and factors like age, gender, occupation, place, time, etc.
** In descriptive studies no hypothesis is formed and no analysis is performed
* Case report
** Description of a case, usually a patient, in a manner which provides information
** Not a true epidemiological study, as only one case is reported
** However, many case reports with similar features may raise suspicion of an underlying epidemic
*** This is how AIDS was discovered
** Example: a report of a patient with a rare disease, or unusual symptoms of a disease
* Case series
** A series of similar patient cases
** Common characteristics between cases can be identified
** Example: a series of cases of patients with the same disease
** A register is a complete set of case series for an area
*** Registers provide information of disease burden in a country
* Cross-sectional studies
** Can be descriptive or analytical
** Concurrent (does not look back or forward in time)
*** The exposure and outcome (disease) are measured simultaneously
** Steps
*** (Randomly) select a study population
*** Divide them into 2 groups depending on whether they currently are exposed to the factor in question
*** Further divide these 2 groups into 2 groups depending on whether they have the disease in question
*** We can now evaluate the association between the factor and the disease
** Advantages
*** Inexpensive
*** No need to wait for the outcome to happen
** Disadvantages
*** Gives odds ratio and prevalence, not incidence
*** Very susceptible to bias
*** Difficult to establish a causal relationship with

[[Category:Public health 2 - General epidemiology and demography]]