Types of epidemiological studies- classification. Descriptive studies. Ecological studies. Cross-sectional studies. Applications in medical practice. (1/2)
Types of epidemiological studies- classification:
1. Observational studies:
Descriptive studies: population, cross-sectional, longitudinal studies —> limited to a description of the occurrence of a disease in a population
Analytical studies: case-control, cohort studies —> analyses relationship betw. health status & other variables
2. Experimental studies: involves an experimental active attempt to change a disease determinant of the progress of a disease
Descriptive studies:
General principles:
starting point for epidemiological investigations = to describe the patterns of distribution of disease —> is the 1st phase of an epidemiological investigation
advantages: cheap, quick, give an initial overview of a problem —> may point to the next step in the investigation
Use:
1. demonstrates the patterns in which diseases & associated factors are distributed in populations
2. identifies changes in mortality & morbidity, compares the incidence or prevalence of diseases in different regions or between groups of individuals with different characteristics
3. studies of this type may give rise to hypotheses of cause
Data used:
Usually: descriptive studies make use of routinely data —> i.e.: data for births, deaths, morbidity
The actual source used for a particular investigation depends on the data that are required —> to receive the data it is necessary to conduct special surveys to collect the raw material for a descriptive study —> usually cross-sectional surveys used
Procedures in descriptive studies:
they observe the distribution of a disease or health-related characteristics in human populations
- a) identify characteristics associated with presence or absence of disease in individuals in defined population
- b) describe occurrence and distribution of disease or health related events
Types of distributions:
- time - when is the disease occurring? —> long-term-trends, periodic changes, epidemics
- place - where is it occurring? —> broad geographical differences, local differences, variations within single institutions
- person - who is getting the disease? —> age, gender, marital status, ethic groups, family, culture, occupation and socio-economic groups
—> 2 or more factors correlate with incidence of a disease and with each other
Procedures involved:
- Defining population —> defined population can be the whole population or a representative sample from or a special selected group (i.e. age, gender)
- Defining disease —> aims to obtain an accurate estimate of disease in population & define it
- Describing disease by time, place, person (siehe oben)
- Measurement of disease —> information about morbidity, disability, mortality & include different subgroups of the population obtained through cross-sectional & longitudinal studies