General Epidemiology

Dr. Akhilesh Bhargava MD, DHA, PGDHRM Prof. Community Medicine & Director-SIHFW, Jaipur : 

Dr. Akhilesh Bhargava MD, DHA, PGDHRM Prof. Community Medicine & Director-SIHFW, Jaipur Principles of Epidemiology

Epidemiology : 

Akhilesh Bhargava 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.

Epidemiology Define ?: 

Akhilesh Bhargava 3 Epidemiology Define ? A study of all diseases/health events infectious/non-infectious acute/chronic communicable/non-communicable. Science of rates expressed as probability “Anything that happens to people ”

Epidemiology: Gen. Objectives: 

Akhilesh Bhargava 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.

Specific Objectives: 

Akhilesh Bhargava 5 Specific Objectives 1. Understanding causation of disease with specific purpose of-- Formulation and selection/rejection of hypothesis. Testing hypothesis through *Survey *Observation studies

Specific Objectives…: 

Akhilesh Bhargava 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

Specific Objectives: 

Akhilesh Bhargava 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

Planning: Terms : 

Akhilesh Bhargava 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.

Goal:: 

Akhilesh Bhargava 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).”

Purpose: : 

Akhilesh Bhargava 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.

Objectives: : 

Akhilesh Bhargava 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

Strategy: 

Akhilesh Bhargava 12 Strategy A strategy is a plan (to choose) to achieve a particular goal or result; and reveals the logic of your choices.

Approach: : 

Akhilesh Bhargava 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.

Monitoring : 

Akhilesh Bhargava 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

Evaluation : 

Akhilesh Bhargava 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

Epidemiology: Basic approach: 

Akhilesh Bhargava 16 Epidemiology: Basic approach Counts cases (events). Defines involved population. Determines rates/proportions Compares rates. Makes inferences

Epidemiology?: 

Akhilesh Bhargava 17 Epidemiology? “ Study of distribution and determinants of health related state or events & disease in human population” “Science of rates expressed as probability”

Uses of Epidemiology: 

Akhilesh Bhargava 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

Uses of Epidemiology: 

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

Epidemiological studies: 

Akhilesh Bhargava 20 Epidemiological studies Descriptive Correlation studies Individual studies Analytical Case control studies Cohort studies Experimental Randomized design Blind Double blind Triple blind Clinical trials

Epi. Studies- Types: 

Akhilesh Bhargava 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

Descriptive Epidemiology?: 

Akhilesh Bhargava 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.

Descriptive Epidemiology: Objectives: 

Akhilesh Bhargava 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

Descriptive Epidemiology describes-: 

Akhilesh Bhargava 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

Reasons for changes in Trends: Real: 

Akhilesh Bhargava 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

Reasons for changes in Trends: Artifactual: 

Akhilesh Bhargava 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

Descriptive Epidemiology: 

Akhilesh Bhargava 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)

Slide 28: 

Akhilesh Bhargava 28 Person: Place: Time: Who? Where? When? Descriptive Epidemiology

Who (Person) ? Is getting the disease: 

Akhilesh Bhargava 29 Who (Person) ? Is getting the disease Attributes & Variables Age Sex Ethnicity Marital status Occupation Education Income group…………

Age: 

Akhilesh Bhargava 30 Age Malnutrition Arthritis/ Cancer STI Measles

Slide 31: 

Akhilesh Bhargava 31 Gap starts narrowing after 54 (menopause), suggests protective effect of estrogen Sex

Where (Place) ? Where Rates are highest and lowest: 

Akhilesh Bhargava 32 Where (Place) ? Where Rates are highest and lowest Residence Occupation/ Work place At specific events Geographic sites

Time (When) ? Reflects on trend: 

Akhilesh Bhargava 33 Time (When) ? Reflects on trend Year Season Day Date of Onset Duration

Time trends : 

Akhilesh Bhargava 34 Time trends Secular (Changes that occur over long periods of time) Periodic (short term) Cyclic (Seasonal) Epidemic

Secular trend is influenced by:: 

Akhilesh Bhargava 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

Cyclic (Seasonal) trends: 

Akhilesh Bhargava 36 Cyclic (Seasonal) trends Changes in frequency over: Days, Weeks , Months , Years

Periodic (short term): 

Akhilesh Bhargava 37 Periodic (short term) Changes that occur in hours/ days / weeks Simultaneous exposure to single source (Point source) John Snow- Cholera

Endemic vs. Epidemic: 

Akhilesh Bhargava 38 Endemic vs. Epidemic No. of Cases of a Disease Time Endemic Epidemic

Let us make an educated guess: Hypotheses: 

Akhilesh Bhargava 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

Developing Hypotheses: 

Akhilesh Bhargava 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

Developing a hypotheses: 

Akhilesh Bhargava 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