General EpidemiologySix Honest Serving Men :General EpidemiologySix Honest Serving Men ? What Why When How Where Who


Definition of Epidemiology The study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems :Definition of Epidemiology The study of the distribution and determinants of disease frequency in human populations and the application of this study to control health problems


Slide 3:Epi = among Demos = people Logos = study


3 Components :3 Components Disease Frequency Disease Distribution Disease Determinants


Disease Frequency :Disease Frequency Measurement of frequency of disease, disability or death Rates and Ratios (prevalence rate, incidence rate, death rate etc.,) Measurement of health related events and states ( Health needs, demands, activities, tasks, health care utilization) Measurements of variables


Disease Distribution :Disease Distribution Patterns of the disease distribution By time, place and person Out come – Formulation of Hypothesis Known as Descriptive Epidemiology


Disease Determinants :Disease Determinants To test aetiological Hypothesis To identify underlying causes (risk factors) Known as Analytical Epidemiology Helps in developing Health programmes, interventions and Policies Helps in understanding Chronic Diseases eg., Lung cancer, CVD’s.


Slide 8:Epidemiology Vs Clinical Medicine


Epidemiological approach :Epidemiological approach Asking Questions Making Comparisons


Asking questions :Asking questions Related to Health Events: What is the event (problem)? What is the magnitude ? Where did it happen ? When did it happen ? Who were affected ? Why did it happen


Related to Health Action :Related to Health Action What can be done to reduce this problem and its consequences? How can it be prevented? What action should be taken by the community? By other sectors? Where and for whom these activities be carried out? What resources are required? How are the activities to be organised? What difficulties may arise, and how might they be overcome?


Making comparisons :Making comparisons Between two ( or more groups) One group having the disease and the other group not having the disease Comparison between individuals


Comparability :Comparability Like can be compared with like Age and Sex or other variables Randomization or random allocation Matching Standardization


Basic measurements in epidemiology :Basic measurements in epidemiology Measurement of mortality Measurement of morbidity Measurement of disablity Measurement of natality Measurement of presence or absence or distribution of characters or attributes of the disease


Slide 15:Measurement of medical needs, health care facilities, utilisation of services and other health related events Measurement of presence or absence or distribution of the environmental and other factors suspected of causing the disease Measurement of demographic variables.


Tools of measurements :Tools of measurements Rates Ratios Proportions


Rate :Rate 500 deaths from motor vehicle accidents in city A during 1985 For comparison between City A and City B calculate Rate Rate measures the occurrence of some particular event in a population during a given time period.


Slide 18:Death Rate: Specific Rate: Disease specific, age-group specific, specific time periods Standardized rates: By direct method and indirect method


Ratio :Ratio Expresses a relation in the size between two random quantities. Numerator is not a component of denominator X : Y = X/Y


Proportion :Proportion A proportion is a ratio which indicates the relation in magnitude of a part of the whole. Numerator is always included in the denominator. Usually expressed as percentage.


Adjusted or standardized rates :Adjusted or standardized rates Direct Standardization Indirect standardization


Direct Standardization :Direct Standardization Select a standard population A standard population is defined as one for which the numbers in each age and sex group are known. Apply to the standard population, the age-specific rates of the population whose crude death rate is to be adjusted or standardized.


Proportion of heavy smokers in cases and controls :Proportion of heavy smokers in cases and controls


Age adjusted proportions :Age adjusted proportions


Measurement Morbidity :Measurement Morbidity “ any departure, subjective or objective, from a state of physiological well-being” Sickness, illness, disability Frequency Duration Severity


Incidence :Incidence “ the number of new cases occuring in a defined population during a specified period of time” Number of new cases of specific disease during a given time period = --------------------------------------------- X 1000 Population at risk during that period


Slide 29:500 = -------- X1000 = 16.7 per 1000 per year 30,000


Special incidence rates :Special incidence rates Attack rate Secondary attack rate: the number of exposed persons developing the disease within the range of incubation period following exposure to a primary case


Uses of incidence rate :Uses of incidence rate Useful for taking action A) to control disease B) for research into etiology and pathogenesis, distribution of diseases, efficacy of preventive & therapeutic measures


Prevalence :Prevalence All current cases (old & new) existing at a given point of time, or over a period of time in a given population Definition: the total number of all individuals who have an attribute or disease at a particular time divided by the population at risk of having the attribute or disease at this point in time or midway through the period


Slide 33:Point prevalence: the number of all current (old and new) cases of a disease at one point in time in relation to a defined population. Number of all current (old &new) cases of specific disease existing at a given time period = ----------------------------------------------------- X 100 Estimated Population at the same point of time


Period prevalence :Period prevalence


Period prevalence :Period prevalence Period prevalence: the number of all current (old and new) cases existing during a defined period of time expressed in relation to a defined population. Number of existing cases (old &new) cases of a specified disease during a given period of time interval = ----------------------------------------------------- X 100 Estimated mid-interval Population at risk


Slide 36:Case -1 Case -1 Case -3 Case -5 Case -6 Case -8 Case -2 Case -4 Case -7


Slide 37:Incidence would include cases – 3,4,5, & 8 Point prevalence ( Jan 1st) – 1,2, & 7 Point prevalence (Dec 31st) – 1,3,5 and 8 Period prevalence ( Jan – Dec ) cases 1,2,3,4,5,7 and 8


Slide 38:P = I X D = incidence X mean duration Incidence = P / D Duration = P / I


Epidemiological methods :Epidemiological methods Observational studies a) Descriptive studies b) Analytical Studies Experimental studies / Intervention studies a) Randomized Control Studies b) Field trials c) Community trials


Descriptive studies :Descriptive studies When is the disease occurring? Time distribution Where is it occurring? Place distribution Who is getting the disease? Person distribution


Procedures in descriptive studies :Procedures in descriptive studies Defining the population to be studied Defining the disease under the study Describing the disease by Time Place Person 4. Measurement of disease Comparing with known indices Formulation of aetiological hypothesis


Defining the population :Defining the population Total Number Age composition Sex composition Occupation Cultural characters


Describing the disease :Describing the disease Clinical definition Operational definition


Time distribution :Time distribution Short term fluctuations Periodic fluctuation Long term or secular trends


Short term fluctuations :Short term fluctuations Types of epidemics Common source epidemics a) Single exposure or ‘point source” epidemics b) Continuous or multiple exposure epidemics Propagated epidemics person – to – person arthropod vector animal reservoir Slow (modern) epidemics


Defining the population :Defining the population