801 Midterm Notes 1-9 PDF

Week 1 801 Introduction to Epidemiology Public/population health - “public health is defined as “the art and science of preventing disease, prolonging life and promoting health through the organized efforts...

Week 1 801 Introduction to Epidemiology Public/population health - “public health is defined as “the art and science of preventing disease, prolonging life and promoting health through the organized efforts of society” (Acheson, 1988, WHO)” - “population health is an approach to health that aims to improve the health of the entire population and to reduce health inequities among population groups. In order to reach these objectives, it looks at and acts upon the broad range of factors and conditions that have a strong influence on our health” Population health approach - A population health approach considers the entire range of individual and collective factors and conditions- and their interactions- that have been shown to be correlated with health status - Determinants of health o Income and social status o Social support networks o Education o Employment and working conditions o Social environments o Physical environments o Bio and genetic endowment o Personal health practices and coping skills o Healthy child development o Health services o Gender o Culture Population health approach - Demographic focus o Action is directed at the health of the entire pop, or sub-pop, rather than individuals - Strategies and settings o A pop health approach uses a variety of strategies and settings to act on the health determinants in partnership with sectors outside the traditional health system or sector - Broadened definition of health o Health is a capacity or resource rather than a state (of physical, mental, and social wellbeing) which is embedded in social, economic and physical environments. - change is not just based on individual but a variety of hierarchical categories - A number of forces at play which can act at different levels on this pyramid. The pyramid most of the healthcare interventions happen more higher up, changes to health care systems happen at top but PH interventions happen mostly at bottom at physical and social environmental exposures What is social justice? - Equal access to wealth, opportunities, privileges within a society - Social inequality: the condition of unequal access to the benefits of belonging to a society. In a purely equal society, every citizen is equally able to contribute to the overall well-being of that society, and they are equally able to benefit from their membership within that society Does public health= social justice? - Striving towards more social justice - Social justice strives for equality while public health is more equity - “we cant achieve good public health outcomes without taking action to ensure all members of our community have access to an equitable lived experience. This means that public health must have a social justice lens” - Frame population health in the context of social justice - Health disparities are created by inequities. The social determinants of health (SDOH)< such as racism, indigeneity, income, gender discrimination, and other factors, create conditions and inequitable circumstances which disproportionately impact black ,indigenous, and LGBTQ2S+ communities, people living in poverty, people who use drugs and many more - Examine health outcomes through a social justice lens which takes sdoh into consideration Epidemiology and public health - Public health is usually about identifying health problems within a community and resolving them - Epidemiology is fundamental in: o Providing the data needed to make public health judgements o Describing and comparing groups of people o Controlling for multiple influential health modifiers in a systematic and logical way o The science of measuring and counting, systematic ways of thinking through Epidemiology: the study of that which befalls (afflicts) the people (a population) - ancient Greek roots: - Epid= on, upon, befalls - Demos= the people (democracy) - Ology= the study of What is epidemiology? Epidemiology is: - The study of the distribution and determinants of health related states or events in specified populations and the application of this study to the control of health problems - The who? What? Where? When? And why? Of health A bit of history - John Graunt (1620-1674) o Credited with coming up with the quantitative approach o Quantitative approach to mortality o Study of parish christening records and ‘bills of mortality’(death and birth rates) o Sex differences in mortality; seasonality o Numerical accounts of the effects of plague in London o Constructed the first life table o First to calculate life expectancy - James Lind (1716-1794) o Scottish naval surgeon o Conducted experiment with 12 sailors with scurvy That citrus fruit could cure it o Had hypothesis that acidic supplement would help prevent or treat it o 6 pairs of sailors each received a different treatment o Pair receiving oranges and lemons recovered o Argued for better hygiene and air on ships (preventative medicine and nutrition) - Edward Jenner (1749-1823) o English physician o Observed that dairy maids developed cowpox and that they did not develop smallpox during outbreaks o Cowpox material used as vaccination o Inoculated Neighbours son with the pus of cowpox “pareolus material” o smallpox vaccine (very small amount of smallpox that was active) would prevent substantial amounts of smallpox o ‘father of immunology’ - John snow (1813-1858) o English physician o Believed cholera was transmitted through contaminated water o Traced local cholera epidemic to a public pump o Thinking of modern day epidemiologists do to determine causality o Was able to show it could spread person to person, and through water  o (earlier beliefs thought disease spread through miasma dirty air) linked bad outbreak around BroadStreet used spot map to show the spread of cases in relation to the pump and other regions - Majority of cases happened to arrive from the broad street pump - Interviewed families- 5/10 cases always used the water from that pump 8/10 used water from that pump - Was also able to explain why some living around did not get it (had their own water pump) - Work led to convincing of officials to break the handle of the pump - graph showing the epidemic curve - Know that it was due to the pump because there was not a resurgence - However residents fled the city so this graph the rate may be inaccurate (must know that the denominator did not change over time) - Difference between counts and rates Objectives of epidemiology - Description: to determine the extent of disease found in the community - Causation: to identify the causes of a disease (=risk factors for that disease o Epi must known for trying to figure out causation (difficult when not caused by one cause) - To evaluate interventions- new preventative an therapeutic measures and new modes of health-care delivery - To study the natural history and prognosis of disease - To provide the foundation for public policy Types of epidemiology - Descriptive o To describe disease by person, place and time o To measure the burden of disease - Analytic o To look for associations between exposure and disease i.e. to establish causation - Intervention o To evaluate new interventions o To monitor intervention programs in practice Descriptive-describe and compare patterns of disease by person, place and time - How do mortality rates compare between indigenous and other Australians? - How does Australia's death rate from heart disease compare with those of other countries? - How have patterns of disease changed over the past century?  - Standardized mortality ratio; of 1 suggests that the two groups being compared have equal rates of risk. In this graph the rates are always greater than 1 therefore indigenous experience much worse health outcomes - Standardization adjusts for different age distributions within the countries - Epidemiological transition (rise of chronic diseases not as many infectious diseases) - However in Canada cancer is worse than heart disease which is different from united states - Analytic- identify associations between ‘exposures’ and disease - What is the relationship between smoking cigarettes and death rates due to lung cancer?  - Longitudinal study, enough to make a statement about cigarettes Intervention – evaluate new interventions or prevention programs - Does fluoridation of water prevent dental caries Epidemiology and public health - Identify and quantify health problems in the community - Identify the cause of a problem - Test solutions to prevent or reduce the problem - Evaluate the solution in practice - Epidemiologists work with professionals in other disciplines (statistics, sociology, environmental science, economics, management, psychology) to maximize the public’s health Evidence-informed decision making: a guiding framework for public health video Helpful Website: National Collaborating Centre for Methods and Tools (NCCMT and videos) Evidence-Informed Decisi on Making: A guiding fram ework for public health video on YouTube URE model - Illustrates that many different kinds of evidences influence ph decisions - Research, community health issues and local context, community and political preferences and actions, public health resources that come to public health expertise - Flexible model to emphasis on different types of evidence Watch this video and write notes What is evidence-informed public health?  - The process of distilling and disseminating the best available evidence from research, context and experience, and using that evidence to inform and improve public health practice and policy A model for evidence-informed decision making in public health Two of the four types of evidence What constitutes evidence for public health? 1) Best available research evidence: information derived from scientific inquiry to identify determinants of health/disease and inequities, or that assesses whether or not a prevention program, practice, or policy is achieving its intended outcomes 2a) Contextual evidence: collection of measurable factors in the community that may impact the success of a prevention strategy (community history, organizational capacity, social norms, etc.. Role: to provide information to help determine whether a prevention strategy is likely to be acceptable, feasible, and useful in a local setting 2b) Experiential evidence: collective experience and expertise of those who have practiced or lived in a particular setting, including knowledge of subject matter experts Extra Material The Epidemiologic approach: Epidemiologic tools and skills 1. How much [disease] is occurring? a. Measures of disease occurrence such as incidence rate incidence proportion and prevalence (or mortality rates) 2. How does the burden of [disease] in your area compare with that in other areas? a. Divide measures of disease occurrence into categories of age (age-specific), or sex (sex-specific), or standardise to make populations comparable 3. What causes the occurrence of [ disease] to vary within your population? a. Measures of association such as relative risk and odds ratio 4. What types of investigations are done to study the aetiology and control of [disease]? a. Different study types  5. How do we evaluate whether the study results are valid? a. Consider threats to validity such as change, bias and confounding 6. How do we assess whether associations between potential aetiologic factors and [disease] are causal? a. Consider relevant aspects of the association to assess causality (some subjective judgements must be made) 7. How much morbidity and mortality might be prevented by interventions? a. Evaluate the benefits and harms of intervention programs such as screening b. Understand measures of diagnostic accuracy and predictive values c. Quantify the effect of reducing or eliminating risk factors on the population disease burden using measures such as population attributable risk 8. How do we use the results of studies to make decisions? a. Understand the fallibility of a single study and the methods used to integrate findings from several studies. Epid 801 Week 2 Measures of Disease Occurrence September 9, 2024 Objectives 1. Define incidence and prevalence and the relation between them 2. Calculate and use the fundamental measures of disease occurrence: incidence rate, incidence proportion (or cumulative incidence) and prevalence a. Most important health measures 3. Define and use the terms: population at risk, person-time, loss to follow-up Why measure health? - One of the fundamental tasks to epidemiological research is to quantify the occurrence of disease - Why? o May help hypothesize causes, spur further investigation, planning for interventions, monitor effectiveness of interventions o Compare level of disease with other pops o Assess the need for interventions o Monitor responses to control efforts What are we measuring? - Diagnosis is based on: o Symptoms- subjective, reported by patient o Signs- objective, observed by clinician (grading criteria) o Tests - To make comparisons we need to use the same diagnostic criteria i.e. a clear ‘case definition’ - Different criteria may give different results.. - Risk and Incidence Proportion (cumulative incidence) - To compare levels of disease among groups of individuals, time, frames, or locations, we need to consider counts of cases in context of the size of the population from which those cases arose - ‘I had 10 calves die of respiratory disease last week’ o But how many calves do they have? If there are 20 calves that's terrible If there are 40 000 that's a good number Incidence - Deals with what is new - Number of new events or cases of disease that develop in a pop of individuals at risk during a specified time interval - There are two specific types of incidence measures: o Incidence proportion (also referred to as cumulative incidence) o Incidence rate (person-time) Incidence Proportion - Incidence proportion = average risk - ”the only way to interpret risk is to know the length of the time period over which the risk applies” - Synonym: cumulative incidence  - Onset of disease, risk of death of given disease, event that marks a health outcome What does this statement mean? - Women who are 60 years old have a 2% risk of dying of cardiovascular disease - You need to frame this in the context of length of time: if its over the next 24 hours that's catastrophic but if over lifetime that's low - May be true for some specific period of time but unlikely over remaining lifetime - Without providing the length of time over which the risk applies, risk values are not meaningful (Rothman, 2012) Risk - Combination of many factors which determines the shape of those curves - New cases occurring - Example A: might plateau with vaccinations so infectious disease - Example B: risk of dying associated with age, so risk is age. Or chronic diseases tend to be quite exponential - Risk can vary over time and is a function of the natural history of the disease (its latency or incubation period etc.) Denominators/population at risk - Should only include those at risk of developing the disease/event (in practice this is difficult but it is ideal) - Examples: o Endometrial cancer rates: women with an intact uterus (difficult to exclude this from census data) o Work-related injuries: workforce population only - Often difficult to get a true estimate of the population of those at risk o Published cancer incidence rates use census population figures so they are underestimates- why? Some people in census have already been diagnosed, including is not accurate for incidence rate Includes those at risk and not at risk for cancer, so risk is underestimated Incidence proportion - Incidence proportion assumes that entire population at risk followed up for specific time period - IP = 7/12 Per year - = 0.58 per year - Just over 0.58 women will get it in a year, 5.8 in 10 years, 58 in 100 years - Its assumed that everyone in that study was followed for the whole time period - Cumulative incidence is unitless, has no units associated, but need to contextualize time period - Example: quantify risk of sudden death from heart attack among joggers: o 10 000 joggers o Followed for 5 years o Total of 50 heart attacks over 5 years - Cumulative incidence: = ? 50/ 10 000 = 5 per 1000 or 0.5% over a 5 year period Group exercise  - Why is the time period important? o The denominator, have to know it in the context of time, if it was 1 year vs 20 it would be much more concerning vs not as concerning o Gives perspective on the severity - What would happen if you didn't have follow-up info on all 10 000 joggers? o Have bias because you don't know if or if they did not have the event occur - How would the risk estimate change if the follow up period were 20 years? o Would be less risk overall o Competing risks (other factors that might remove you from being at risk of a heart attack) - Interpretation of results would be very different if 0.5% among joggers referred to 6 month period, 5 year period or 20 year period - Length of follow up will not be uniform for all participants - Subjects may be lost to follow up so info not available (not complete) Incidence proportion - Not an accurate estimate of risk unless all subjects in the study pop are followed for the entire follow up period - Total follow up rarely occurs because individuals often leave the population for a variety of unrelated reasons (migration, competing risks, etc.) - If we don't account for these losses then the cumulative incidence estimate is biased Person-time incidence rate - Rate: instantaneous concept (like speed) incidence rate is analogous to the average speed of a car at a particular point in time, e.g. 60 km/hr. o Instantaneous rate of that car o - Denominator: o Is a measure of time o The sum of each individuals time at risk and free from disease Rate: example - Incidence rate of tetanus in France in 1995 o Tetanus diagnoses (cases): 17 o Population in 1995: 58 million o Incidence rate = 0.029/100,000/year - Rate may be expressed in any power of 10 o 100; 1000; 10 000; 100 000 Incidence rates (person-time) - Example: prostate cancer - 10 000 men enrolled Jan 1997 no evidence of prostate cancer, yearly screening for 5 years - Numerator: total number of cases (add it up) - Denominator: total person time (years) o Sum of the times is the denominator  - (10 + 15 + 20 + 25 +30)/ 39 2000 = 2.6 per 1000 person-years - For cancer usually by 100 000 person years Incidence rate is an instantaneous concept (speed at which disease is occurring) - 0.3 cases of disease per person-month is the same rate as 3.6 cases per person-year - Choice of units in the denominator should depend on: o The ease of understanding Example: 3.6 per person year is easier to grasp o Usual units that such a rate is reported by Example: cancer which is relatively rare is usually reported using per 100 000 person-years Cumulative incidence (CI) versus person time incidence rate (IR) - Incidence proportion (or cumulative incidence) measures average risk of developing the disease over a certain time period - IR (or incidence density) measures rate at which disease is occurring in a population - IR provides more accurate estimates of rates o Can account for loss of subjects/ competing risks o IR allows for staggered entry into the study Incidence rate helps you account for this staggered entry Relationship between risk (CI) and incidence rate (person-time) - Necessary assumptions for person-time o Constant rate (steady state) Varies by age o Risk