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