2 Descriptive epidemiology Descriptive epidemiology is the first phase of epidemiological investigation.The study concerns with the description of the health status of a community in terms of time, place and person.
3 Steps in descriptive epidemiology Defining the populationDefining the disease under studyDescribing the disease in terms of time, place and personMeasurement of diseaseComparing with known indicesFormulation of an aetiological hypothesis
4 Defining the population The defined population can be the whole population in a geographic area or a representative sample taken from it.The defined population can be selected group such as age and sex group, occupational groups, hospital patients, school children etc.The study population needs to be large.
5 Defining the disease under study The disease under studies should be defined in both clinical and epidemiological terms.The 'operational definition' of disease i.e. a definition by which the disease or condition can be identified and measured is important.The case definition according to disease must be adopted throughout the study.
6 Describing the disease The disease occurrence and distribution of disease are described in terms oftimeplacepersonIncludes systematic collection and analysis of data.
7 Time distributionThe disease rate may vary by the time of its occurrence i.e. by week, month, year etc.There are three kinds of time trends of disease occurrence:Short terms fluctuationsPeriodic fluctuationsLong term or secular trends
8 Short term fluctuations Common source epidemics-well of contaminated water; food poisoningPropagated epidemics- person to person, arthropod vector, animal reservoirSlow modern epidemics- road accidents, blood cancer, hypertensionPeriodic fluctuationsSeasonal trendCyclic trendLong term or secular trendsPolio, malaria
9 Place distributionThe geographic distribution of the disease varies because of variation in cultures, standard of living and external environments. The mortality, morbidity varies due to socioeconomic factors, dietary differences, cultures and behavior.International variationsNational variationsRural urban variationsLocal distributions
10 Person distributionThe disease should be described by age, sex, ethnicity, marital status, occupation, social class, behavior, stress, migration etc.Age is probably the single most important personal attribute because almost every health related events or states vary with age.In general, males have higher rate of illness and death than females for a wide range of diseases.
11 Measurement of disease After defining the disease, the disease load should be measured in population.The disease should be measured in terms of mortality, morbidity - prevalence, incidence.Comparing with known indicesThe disease should be compared with known indices such as with data from previous similar studies, national data or national and international standards.Formulation of hypothesisThe descriptive epidemiology helps to formulate hypothesis relating to disease aetiology.The epidemiological hypothesis should specify the population, the causes, the excepted outcome, dose response relationship, time response relationship.