General Epidemiology

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Presentation from Dr. Akhilesh Bhargava

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General Epidemiology

  1. 1. Principles of Epidemiology Dr. Akhilesh Bhargava MD, DHA, PGDHRM Prof. Community Medicine & Director-SIHFW, Jaipur
  2. 2. Epidemiology The study of distribution and determinants of health problems in specified populations and the application of this study to the control of these problems. It is the scientific method of problem solving used by "disease detectives"--epidemiologists, laboratory scientists, statisticians, physicians and other health care providers, and public health professionals--to get to the root of health problems in a community. 2 Akhilesh Bhargava
  3. 3. Epidemiology Define ? vA study of all diseases/health events Øinfectious/non-infectious Øacute/chronic Øcommunicable/non-communicable. vScience of rates expressed as probability v“ Anything that happens to people” 3 Akhilesh Bhargava
  4. 4. Epidemiology: Gen. Objectives • Explaining the Causal mechanism of disease and process of deviation in Health. • Explaining the reason for Local disease occurrence. • Effective planning and administration of Health Care Services. 4 Akhilesh Bhargava
  5. 5. Specific Objectives 1. Understanding causation of disease with specific purpose of-- ØFormulation and selection/rejection of hypothesis. ØTesting hypothesis through *Survey *Observation studies 5 Akhilesh Bhargava
  6. 6. Specific Objectives… 2. Testing validity of rationale of control /intervention programs 3. Classify disease/disability based on : Distribution Causal factors, and Natural history of disease 6 Akhilesh Bhargava
  7. 7. Specific Objectives 4. Explaining local disease pattern 5. Administrative Guidance – In assessing Need, Utilization & Effectiveness – In monitoring & evaluation of control programs (cost effectiveness & cost benefit analysis) – In Logical Planning of • Services • Resources • Programs • Reach & • Risk Approach 7 Akhilesh Bhargava
  8. 8. Planning: Terms • Planning-“an act or process of choosing between alternatives to accomplish preset goals”. • Plan denotes a blue print of action • Program is a strategy with defined Objectives. 8 Akhilesh Bhargava
  9. 9. Goal: • The proposed long-range benefits of the program for a specified area, defined in general terms. A goal is the ultimate objective; for example, “reducing the incidence of HIV in (a country).” 9 Akhilesh Bhargava
  10. 10. Purpose: • The overall objective (also called strategic objective) of the program, for example, “to increase the accessibility to and use of palliative care facilities in (a particular geographic area).” • ultimate measure of the program’s effectiveness. 10 Akhilesh Bhargava
  11. 11. Objectives: • The anticipated outcomes or benefits that are the expected results of implementing a strategy. They are described in measurable terms and indicate a specific period of time during which these results will be achieved. • Should be SMART • specific, • measurable, • appropriate, • realistic, and • time-bound 11 Akhilesh Bhargava
  12. 12. Strategy • A strategy is a plan (to choose) to achieve a particular goal or result; and reveals the logic of your choices. 12 Akhilesh Bhargava
  13. 13. Approach: A statement that describes how the program will achieve its objective. That is, activities that will help the program achieve its objectives most effectively and feasibly. 13 Akhilesh Bhargava
  14. 14. Monitoring • A methodological arm of evaluation that tracks the program’s incremental steps to its effect and informs the final evaluation report. • A continual, routine effort requiring data gathering, analysis, and reporting on results at periodic intervals • Periodic, regular • Focuses on inputs, outputs, process outcomes, work plans • Basic purpose is improve efficiency and adjust work plan 14 Akhilesh Bhargava
  15. 15. Evaluation • A technical activity that measures the program’s impact and effectiveness as a whole. • Is not about assigning a “grade” of success or failure at the end of a project. • Episodic • Focuses on effectiveness, relevance, impact, cost-effectiveness • Basic purpose - improve effectiveness, impact, and future programming 15 Akhilesh Bhargava
  16. 16. Epidemiology: Basic approach • Counts cases (events). • Defines involved population. • Determines rates/proportions • Compares rates. • Makes inferences 16 Akhilesh Bhargava
  17. 17. Epidemiology? “Study of distribution and determinants of health related state or events & disease in human population” “Science of rates expressed as probability” 17 Akhilesh Bhargava
  18. 18. Uses of Epidemiology • Describe Health events • Identify the cause of disease • Identify the Risk factors • Describe clinical pattern of disease and identify syndromes • Identify effective control and/or preventive measures • Risk Approach 18 Akhilesh Bhargava
  19. 19. Uses of Epidemiology • Take suitable administrative measures in- • Assessing Need, Utilization & Effectiveness • Monitoring & evaluation of control programs (cost effectiveness & cost benefit analysis) • Logical Planning of » Services » Resources » Programs » Reach & 19 Akhilesh Bhargava
  20. 20. Epidemiological studies • Descriptive • Correlation studies • Individual studies • Analytical • Case control studies • Cohort studies • Experimental • Randomized design –Blind –Double blind –Triple blind • Clinical trials 20 Akhilesh Bhargava
  21. 21. Epi. Studies- Types Study Alternative Name Unit of Study Observational Descriptive Analytical Ecological Correlation Population Cross sectional Prevalence Individuals case control Case reference individuals cohort follow-up individuals Experimental Intervention Randomized Clinical trial Patients field trials Healthy people Community trials Community intervention community 21 Akhilesh Bhargava
  22. 22. Descriptive Epidemiology? Study of distribution of a disease in a population, and observing the basic features of its distribution in terms of time, place, and person. 22 Akhilesh Bhargava
  23. 23. Descriptive Epidemiology: Objectives • To evaluate trends and allow comparison among different population groups • To provide basis for planning, provision and evaluation of services • To identify problems to be studied by analytical methods 23 Akhilesh Bhargava
  24. 24. Descriptive Epidemiology describes- • Who gets sick and who does not • Where Rates are highest and lowest • Temporal pattern of Disease • Seasonality • Secular trends decided by changes in- • Diagnostic techniques • Denominator data • Age distribution of population • Survival • Actual incidence 24 Akhilesh Bhargava
  25. 25. Reasons for changes in Trends: Real • Changes in Age distribution of population • Changes in Survival pattern • Changes in Actual incidence for • Genetic • Environmental factors 25 Akhilesh Bhargava
  26. 26. Reasons for changes in Trends: Artifactual • Errors in Numerator due to- • Changes in disease recognition • Change in classification of cause • Change in classification codes of cause of death • Changes in accuracy of reporting age at death • Errors in denominator due to errors of enumeration • ICD-10 has 8000 categories as compared to 4000 in ICD-9 26 Akhilesh Bhargava
  27. 27. Descriptive Epidemiology Descriptive epidemiological approach attempts to describe the disease in terms of its attributes & variables and answers the questions like- • Who (Person) • Where (Place) • When (Time) 27 Akhilesh Bhargava
  28. 28. Descriptive Epidemiology Person: Place: Time: 28 Akhilesh Bhargava
  29. 29. Who (Person) ? Is getting the disease Attributes & Variables • Age • Sex • Ethnicity • Marital status • Occupation • Education • Income group………… 29 Akhilesh Bhargava
  30. 30. Age Malnutrition Measles STI Arthritis/ Cancer 30 Akhilesh Bhargava
  31. 31. Sex Deaths per 100000 population from CAD 800 Deaths per 100000 700 600 500 Men 400 300 Women 200 100 0 Age groups 5-14 15-24 25-34 35-44 45-54 55-64 <1 1-4 Gap starts narrowing after 54 (menopause), suggests protective effect of estrogen 31 Akhilesh Bhargava
  32. 32. Where (Place) ? Where Rates are highest and lowest • Residence • Occupation/ Work place • At specific events • Geographic sites 32 Akhilesh Bhargava
  33. 33. Time (When) ? Reflects on trend • Year • Season • Day • Date of Onset • Duration 33 Akhilesh Bhargava
  34. 34. Time trends • Secular (Changes that occur over long periods of time) • Periodic (short term) • Cyclic (Seasonal) • Epidemic 34 Akhilesh Bhargava
  35. 35. Secular trend is influenced by: • Changes in completeness of source of data • Changes in diagnostic ability • Experience • Techniques • Changes in data classification approach (ICD-9 to ICD-10) • Demographic changes in population • Changes in environment other than that which is related to disease • Changes in clinical concepts, Diagnosis, Terminology 35 Akhilesh Bhargava
  36. 36. Cyclic (Seasonal) trends Changes in frequency over: Days, Weeks, Months, Years Seasonal trend-Malaria & Pf cases, 1994 Rajasthan 80 Jan 70 Feb 60 Mar Apr 50 May % 40 Jun 30 July August 20 Sep. 10 Oct. 0 Nov. Pf cases Malaria Cases Dec. Months 36 Akhilesh Bhargava
  37. 37. Periodic (short term) • Changes that occur in hours/ days / weeks • Simultaneous exposure to single source (Point source) 12 • John Snow- Cholera 10 No. of cases 8 Cases 6 4 2 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Time 37 Akhilesh Bhargava
  38. 38. Endemic vs. Epidemic No. of Cases of a Disease Epidemic Endemic Time 38 Akhilesh Bhargava
  39. 39. Let us make an educated guess: Hypotheses • Why some people get the disease and others do not • Why disease occurs in some places and not others • Why disease occurs at some time and not at others 39 Akhilesh Bhargava
  40. 40. Developing Hypotheses • Interrogate usual suspects! • Source of agent • Mode of transmission • Usual reservoirs • Known risk factors • Exposures that caused disease • Look at person, place and time for clues 40 Akhilesh Bhargava
  41. 41. Developing a hypotheses • Requires familiarity with disease • Hypothesis should be testable • Still clueless? • Talk with cases again • Visit cases in their own situation • Don’t forget outliers 41 Akhilesh Bhargava

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