180507P - INTRODUCTION TO THE DISCIPLINE OF EPIDEMIOLOGY and EPIDEMIOLOGICAL MEASUREMENTS

Presentation at a Nurses Research Program at KFMC Riyadh May 7, 2018 by Professor Omar Hasan Kasule Sr MB ChB (MUK), MPH (Harvard), DrPH (Harvard). Professor of Epidemiology King Fahad Medical City

EPIDEMIOLOGY: DEFINITION:

• Epidemiology is the study of the distribution and determinants of both disease and injury. 
• Two triads are involved in epidemiology: (a) the agent, host, and environment triad and the time, place, and person triad. 
• The primary goals of epidemiology are prevention, control, and, in rare instances, eradication of disease and injury. 
• Epidemiology started as a study of epidemics and extended to cover infectious diseases and later non-infectious diseases. It has now become a methodological discipline that is used to study disease and non-disease phenomena. 

EPIDEMIOLOGY: CLASSIFICATION - 1:

• Qualitative epidemiology deals with qualitative descriptions. Quantitative epidemiology deals with numerical descriptions. 
• Observational epidemiology is based on the observation of human phenomena. Experimental epidemiology involves the assessment of the effects of intervention against a disease phenomenon.
• Descriptive epidemiology describes the patterns of disease occurrence in terms of place, time, and person. Analytic epidemiology seeks to discover the underlying causes of diseases. 

EPIDEMIOLOGY: CLASSIFICATION - 2:

• Public-health epidemiology deals with preventive medicine. 
• Clinical epidemiology deals with the diagnosis, management, and prognosis of the disease. 
• Hospital epidemiology deals with nosocomial infections and other aspects of hospital operations that can be studied using the epidemiological methodology. 
• Drug or pharmaco-epidemiology studies phenomena of adverse reactions and side-effects of drugs. 
• Genetic epidemiology studies the patterns of inheritance of disease from parents and how genetic and environmental factors interact in the final pathway of disease causation.
• Molecular epidemiology deals with phenomena at the molecular level. 
• Occupational epidemiology studies diseases due to exposure to hazardous material or working conditions in the workplace. 
• Environmental epidemiology studies the impact of air, water, and soil pollution on health. 

EPIDEMIOLOGIC METHODOLOGY - 1:

• Epidemiological methodology, following the scientific method, is empirical, inductive, and refutative. 
• Epidemiology relies on and respects only empirical findings. Empiricism refers to reliance on physical proof. Induction is building a theory on several individual observations. 
• Refutation is basically the refusal of a supposition until it is proved otherwise. An epidemiological investigation is not as deterministic as laboratory investigation but is cheap and easy. 

EPIDEMIOLOGIC METHODOLOGY - 2:

• An epidemiologic investigation proceeds through identifying and describing a problem, using the scientific method to formulate and test hypotheses, and interpreting findings. 
• Epidemiological information is sourced from existing data or studies (observational or experimental). There are 3 types of observational studies: cross-sectional, case-control, and cohort (follow-up) studies.  
• There are two main types of experimental studies: community randomized study and clinical trials

ETHICO-LEGAL ISSUES IN EPIDEMIOLOGY:

• Approval by IRB
• Informed consent
• Benefits vs risks
• Privacy and confidentiality
• Conflict of interest
• Study interpretation and communication

DEFINITION OF HEALTH and DISEASE:

• Health is a state of physical, social, psychological, and spiritual well being
• The disease is an abnormality of structure or function
• Illness is the subjective feeling about disease
• Public health is the sum of all official (government) efforts to promote, protect, and maintain health and has 2 main paradigms: disease prevention & health promotion. 
• Community Health involves both private and public efforts of individuals, groups, and organizations to promote, protect, and preserve the health of those in the community. It involves community development, community organization, community participation, and community diagnosis.

MEASUREMENT OF DISEASE OCCURRENCE AS RATES:

• A rate is the number of events in a given population over a defined time period
• The rate has 3 components: a numerator, a denominator, and time. The numerator is included in the denominator.
• A crude rate for a population assumes homogeneity and ignores subgroups' differences. 
• Rates can be specific for age, gender, race, and cause. 
• An Adjusted or standardized rate is a representative summary that is a weighted average of specific rates free of the deficiencies of both the crude and specific rate
• Life expectancy is a form of age-standardized standardized 

MEASUREMENT OF DISEASE OCCURRENCE AS RATIOS:

• The ratio is generally defined as a: b where a= number of cases of disease and b = number without the disease. 
• Examples of ratios are: the maternal mortality ratio and the fetal death ratio.
• The maternal mortality ratio is the total number of maternal deaths divided by the total live births. 
• The fetal death ratio is the ratio of fetal deaths to live births.

MEASUREMENT OF DISEASE OCCURRENCE AS PROPORTIONS (PREVALENCE):

• A proportion is the number of events expressed as a fraction of the total population at risk without a time dimension. 
• The formula of a proportion is a/(a+b) and the numerator is part of the denominator. 
• The term prevalence rate is a common misnomer since prevalence is a proportion and not a rate. 
• Prevalence describes a still/stationary picture of the disease. 
• Like rates, proportions can be crude, specific, and standard. 

MEASUREMENT OF EXCESS DISEASE:

• The odds ratio expresses excess disease in the exposed compared to the unexposed
• The risk ratio
• The risk difference
• Measuring the occurrence of disease. 
• Measures of excess disease risk (Estimating risk determining association).
• Ethical and professional issues in epidemiology.