Epidemiology methods, approaches and tools of measurement
- 1. Epidemiology Swapnil salve Msc first year MTCN MGM college of nursing
- 2. Definition and meaning • What is the meaning of epidemiology? Epidemiology comes from greek word Epi means among the people and demos means the people or population It is the study among or upon the people
- 3. Definition Definitions are, The study of the frequency, distribution and determinants of health related states or events in specified population and application of this study to control health problems. -- (John M Last, 1988)
- 4. Approaches of epidemiology • The epidemiological approach to problem of health and disease is based on:- • Asking questions • Making comparison
- 5. Asking question approach • Asking question • In this, the researcher or epidemiologist ask variety of questions and getting answers that arouses further question and answer. • Questions such as magnitude, nature, extent, geographical distribution and time when it occurs. Ex. Of questions are, • What are the actual and potential health problems and their characteristics? • Which problem have declined? • Which population is at risk? • Where are they in terms of place?
- 6. Making comparison • This method is to make comparison and draw inference (conclusion) • Comparison may be • Between different proportion • Rural population with urban group population • Between sub group of population • Male with female group of population • Comparison between various periods of observation • Different seasons
- 7. Tools of measurement • Tools of measurement is used to test the magnitude of disease • Rate • Ration • Proportion What is rate? Rate is the measure of occurance of some particular events in a population during a given a period of time, death rate, birth rate or accident rate. Ex. Death rate = no of deaths in one year mid year population * 1000
- 8. Tools of measurement • Ratio Ratio is the relation in size between two quantities. It is expressed in the form of 1:1 or 1:600 (means of 1 WBC relative to 600 RBC in body) • Proportion Proportion is a ratio which indicates the relation in magnitude a part of the whole. Ex. No of delinuetes / total no of juveniles * 100
- 9. Epidemiology methods Epidemiological methods are applied to know, • Disease etymology and risk factor • Pattern of spread of infection • Forming hypothesis • For purpose of prevention Methods are, 1. Observational studies 1. Descriptive study 2. Analytical study 2. Experimental study / Interventional study
- 10. Descriptive Study • What is descriptive study? • A descriptive study is defined as one group of subject is studied without any comparison group for describing outcomes in terms of its frequency and its distribution according to selected variables related to time, place and person. • It find out • When disease occur • Where it occurs • Who is affected by disease
- 11. Procedure of descriptive epidemiology • Defining the population to be studied • Defining the disease under study • Describing the disease by • Time • Place • Person • Measurement of disease • Comparing with known indices • Formulation of an etiological hypothesis
- 12. Define population • It may be whole population or sample from geographical area • Population should be large enough • Community should stable (without any migration) • It should clear who belong and who does not belong to population Define disease under study • Define the disease is important concern, if not clear then it is source of error in study. • Ex. Tonsillitis defined as clinically as infection caused by streptococcus pyogenes
- 13. Describing disease • Describe disease by, • Time :- year, season, week, day, hour of onset • Place :- duration, climatic zone, country, region, urban and rural community, town, city • Person:- Age, sex, marital status, occupation, education, birth order, blood pressure, personal habits Measurement of disease The disease is measured as morbidity rates in two aspects, incidence rate (occurance rate) and prevalence rate
- 14. Compare with known indices • in this step, comparison between different population (subgroup of same population) • To find etiology and risk groups in population Formation of etiological hypothesis Hypothesis is a supposition , arrived at from observation or reflection. It should clearly state, population, specific cause, expected outcome, dose response relationship and time response relationship.
- 15. Analytical study • In analytical study, the subject of interest is individual and inference is not individual, but to the population from which it is selected. • There are major two types, • Case control study • Cohort study • Case control study • Case control study is used to identify factors that contribute to a medical condition, by comparing people with that condition (cases) with patients who do not have the condition.
- 16. Case control study • Basic steps are, 1. Selection of cases and controls Cases should be newly diagnosed in specific period of time than old cases or in advance stages of disease. 2. Matching 3. Measurement of exposure It is done by interviews, by questionnaire or studying past records of cases such as hospital records. 4. Analysis and interpretation To find out exposure rate in population
- 17. Case control study Advantages • Easy to carry out • Rapid and inexpensive • No risk to subject • No attention required Disadvantages • Problems of bias relies on memory • Accuracy issues • Selection of appropriate is sometime impossible
- 18. Cohort study • Cohort is another type of analytical study which is usually undertaken to obtain additional evidence to support the existence of an association between suspected cause and disease. Indication • When there is good evidence of exposure of disease • When incidence rate of disease is higher among exposed
- 19. Experimental epidemiology Experimental epidemiology is used to test the hypothesis. In this investigator controls one factor, independent variale and measure the subsequent effect on dependent variables. Ex. a) Test the effectiveness of a drug or treatment (therapeutic trial) b) To know the efficacy of a preventive measure or procedure c) To determine the effect of controlling risk factor for a given disorder (intervention trial) on the individual subject
- 20. Randomized control trial 1. To provide scientific proof of etiological (risk factor) 2. To provide a method of measuring the effectiveness of health services for the prevention, control and treatment of disease and improve the health of the community AIMS 1. Drawing up a protocol 2. Selecting experimental population 3. Randomization 4. Manipulation and intervention 5. Follow up 6. Assessment of outcome
- 21. 1. Establishing a probable diagnosis • Establish diagnosis in clinical round • Visit the affected area and collect relevant information • Meet with doctors, patients • Visit all affectd families and collect essential data • Data of expected cases found from surveillance data, clinicians, hospital registers, hospital investigation 2. Verify diagnosis Comparison of data with previous records. The record should be minimum of 3 years. Ex. Lab test, identification of the serotype Steps of investigation
- 22. 1. Define the population at risk • Prepare the map of the area • Counting the population • This is done by studying list of cases from name, age, sex, address, date of onset of illness, signs and symptoms 2. Define and identify cases A case definition is a standard set of criteria for decading wheather an individual should be classified as having the health condition of interest or not. Steps of investigation
- 23. 1. Perform descriptive epidemiology Categoriezed samples based on, • Time :- onset, peak, incubation period, time of exposure. • Place :- place of work, food places, area at risk • Person :- distribution by age, gender, profession etc. 2. Develop hypothesis Hyposthesis should address, a. Source of the agent b. Mode of transmission c. Vector d. Exposure that caused the disease Steps of investigation
- 24. 7. Test the hypothesis It is done by doing analytical study (case control and cohort study) to conclude hypothesis. 8. Refine hypothesis and do additional studies 9. Write report and communicate findings • Report writing involve, • Introduction, background data, methods, results, discussion and recommendation • Report will use in future and serve as knowledge base of epidemiology and public health Steps of investigation
- 25. 7. Control and preventive measure A. General measures • Use of personal protective equipment by health care provider to prevent infection • Ex. Maintain hygien or cleanliness B. Specific measure • Agent :- removing source • Environment • Interupting transmission ex. Waterborn outbreak • Access to safe drinking water and maintain hygienic Steps of investigation
- 26. 1. Define epidemiology 2. Explain scope of epidemiology 3. Explain aim of epidemiology 4. Selection of epidemiological approach 5. Describe methods of epidemiology 6. Enlist tools of measurement 7. Define morbidity and mortality 8. Indicate measurement of morbidity 9. Describe and indicate measurement of mortality Summary