Descriptive Epidemiology

Manish ChaudharyBPH(IOM), MPH( BPKIHS)manish264@gmail.com

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.

Steps in descriptive epidemiology

• Defining the population • Defining the disease under study • Describing the disease in terms of time, place and

person • Measurement of disease • Comparing with known indices • Formulation of an aetiological hypothesis

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.

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.

Describing the disease • The disease occurrence and distribution of disease are

described in terms of – time– place – person

• Includes systematic collection and analysis of data.

Time distribution

• The 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 fluctuations – Periodic fluctuations – Long term or secular trends

• Short term fluctuations– Common source epidemics-well of contaminated

water; food poisoning– Propagated epidemics- person to person, arthropod

vector, animal reservoir– Slow modern epidemics- road accidents, blood cancer,

hypertension

• Periodic fluctuations– Seasonal trend– Cyclic trend

• Long term or secular trends– Polio, malaria

Place distribution

The 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 variations• National variations• Rural urban variations• Local distributions

Person distribution• The 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.

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 indices• The disease should be compared with known indices such as

with data from previous similar studies, national data or national and international standards.

Formulation of hypothesis• The 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.

Thank You