Epidemiology: Cornerstone of Public Health - PDF

EPIDEMIOLOGY: THE CORNERSTONE OF PUBLIC HEALTH Dr. Nitya Kumar “Mortality and Morbidity” by JL Rodriguez 1  Learning outcomes  (Explain the) use of epidemiology to measure population health...

EPIDEMIOLOGY: THE CORNERSTONE OF PUBLIC HEALTH Dr. Nitya Kumar “Mortality and Morbidity” by JL Rodriguez 1  Learning outcomes  (Explain the) use of epidemiology to measure population health  Apply epidemiological methods in practice to measure health  Compare morbidity and mortality using the Global Burden of Disease study  …Explain global differences in health outcomes 2 EPIDEMIOLOGY: BMF THE CORNERSTONE OF PUBLIC HEALTH Lecture: Prof Debbi Stanistreet E-mail: [email protected] “Mortality and Morbidity” by JL Rodriguez What’s the point of epidemiology? “Black Death” by Bruegel, 1560s 4 Definition of Epidemiology 1. “The study of the distribution and determinants of health- related states or events in specified populations..” + 2. “..and the application of this study to control of health problems” Distribution Determinants Descriptive Analytical Epidemiology Epidemiology  Epidemiological methods I Descriptive epidemiology Describes distribution of a What? = health issue disease: Who? = person Where? = place 1) Magnitude of occurrence 2) Three main features When? = time Person How many? = magnitude of Place occurrence Time 6  Epidemiological methods II Analytical epidemiology Key feature = comparison Finds out causes of disease group. Uses hypothesis testing Different study designs  different ways of identifying ‘Hypothesis’ = theorized relationship comparison group. between disease and possible cause This impacts the - analytical epidemiological study STRENGTH of the study measures the association between design. possible cause/exposure/the risk factor and disease. WHY = what caused it 7  Epidemiological methods I Descriptive epidemiology Describes distribution of a What? = health issue disease: Who? = person Where? = place 1) Magnitude of occurrence 2) Three main features When? = time Person How many? = magnitude of Place occurrence Time 8  A) Person (who?) Characteristics Infant mortality rates, by ethnicity, Age 2013 England and Wales Sex Ethnicity Marital status Socio-economic status – education, – occupation – income Behaviour / habits Source: Office for National Statistics 9  B) Place (Where?) Restricted or widespread ? – outbreak, – epidemic – pandemic Climate effects – temperature – humidity – combined effects. Urban/peri-urban/ rural Relation to environmental exposure - water, food supply, etc. 10  C) Time: when?) Usually displayed graphically: – Y-axis  # of cases; – X-axis  time e.g., years or months. – Usually, line graphs or histograms. 11  Change in disease over time can be: Sporadic: Unrelated scattered cases Epidemic: Unusual (beyond normal) increase in incidence Seasonality: – seasonal change in a condition, or injury that conforms to a regular seasonal pattern Cyclic trend: – Recurrent alterations in occurrence, interval or frequency of disease but no during a fixed period Secular trends: Long term changes over years or decades. – Can apply to both infectious and non- infectious diseases 12  When we look for differences over time, we need to ascertain whether they are due to: Chance /Random variability Random variation will occur over time. We use statistical methods to measure how likely it is that variation has arisen by chance. Artefact/ Bias/ Systematic error Such as mistakes made in collecting or organizing the data Changes in sensitivity or specificity of the surveillance system Changes in the perceptions of the public or the health care community about the importance of diagnosing and reporting a particular disease A Real difference True increases or decreases--actual changes in the frequency of the disease (or risk factor) in the population 13  Epidemiological methods I Descriptive epidemiology Describes distribution of a What? = health issue disease: Who? = person Where? = place 1) Magnitude of occurrence 2) Three main features When? = time Person How many? = magnitude of Place occurrence Time 14 Magnitude of Occurrence: Disease Frequency Next lecture in BMF will focus on this Mortality Rates  Crude Mortality Rates (CMR) Crude Mortality Rate Why do epidemiologists tend to avoid using crude mortality rat 16  Standardized mortality rates  CMR cannot be used to compare two populations which have different age and sex composition.  Chance of dying varies by age, sex, race, socioeconomic class and other factors  To compare mortality, first remove differences in age (sex, etc) composition  Standardization  Standardized rates = Adjusted rates 17  Crude and age-standardized mortality rates The age-standardization of rates eliminates the influence of different age distributions on the morbidity or mortality rates being compared. Crude Age- death rate Standardised 1. Sweden has more people > per death rate per 50years 100,000 100,000 2. Brazil has lesser people > 50 Swede 1027.2 429.2 years n 3. Sweden has less people Brazil 695.1