Epidemiology – Block One – Flashcards
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Four Trends in Disorders
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1. Disappearing 2. Residual 3. Persisting 4. New Epidemic
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Secular Trend
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Changes over a year or longer period of time.
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Cyclic Fluctuations
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Changes within a year or season.
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Factors Affecting Reliability of Observed Changes
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1. New Case Definition 2. Aging of general population 3. Changes in the fatal course of the condition. 4. ICD Coding Changes (Redefining the disease) 5. Efficient Surveillance System (Better screening, diagnostic techniques)
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Disappearing Disorders
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Conditions that were once common but are no longer present in epidemic form: Small Pox, Polio, Schistosomiasis japonica
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Residual Disorders
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- Key factors (Risk Factors) are known. - Methods of control not implemented effectively. STDs, Health Problems related to Alcohol and Tobacco use.
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Persisting Disorders
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Disease for which there is no effective method of prevention or known cure. Cancer and mental disorders.
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New Epidemic Disorders
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Diseases that are increasing in frequency. Type II Diabetes, New Influenza strains, obesity
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Three factors that affect population size
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1. Births 2. Deaths 3. Migration
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Types of Population (3)
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1. Fixed - No population change. 2. Dynamic - Increases and decreases 3. Steady - # births = # deaths
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% of US Population 65+
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13.7%
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Epidemiological Transition from Underdeveloped to Developed Countries
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Infectious and Communicable diseases to Chronic, degenerative diseases.
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Operations Research (OR)
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Includes: 1. Needs Assessment 2. Evaluation of Healthcare Utilization
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Program Evaluation
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Uses epidemiological tools to determine how well a health program meets certain stated goals.
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Define: Risk Factor
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Exposure that is associated with the disease.
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Three Criteria for Risk Factors
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1. Frequency of disease varies by category or value of the factor. - Also known as "Dose-Response Relationship) (Ex: light smokers vs. heavy smokers) 2. Risk Factor precedes onset of the disease - Also known as "Temporality" 3. Observed association must not be due to error
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Temporality
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"Risk factor precedes onset of the disease"
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Bradford Hill Criteria for Causality (9)
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1. Strength of Association 2. Time Sequence 3. Consistency of Repetition 4. Specificity 5. Coherence of Explanation 6. Biological gradient 7. Plausibility 8. Experiment 9. Analogy
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Define: Descriptive Studies
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1. Used to identify a health problem 2. Characterize the amount and distribution of disease
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Define: Analytic Studies
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1. Follow Descriptive Studies 2. Used to identify the cause of the health problem.
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Objectives of Descriptive Epidemiology
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1. Evaluate and compare trends 2. Provide a basis for planning, provision, and evaluation of health services. 3. Identify problems for analytic studies (i.e. Generate Hypothesis)
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Characteristics of Persons (7)
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1. Age 2. Sex 3. Marital Status 4. Race and Ethnicity 5. Nativity and Migration 6. Religion 7. Socioeconomic status
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Trends by Age
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1. Childhood - Developmental problems 2. Teenage Years - Unplanned pregnancy, substance abuse 3. Adults - Accidental injury, Homicide, Suicide, HIV 4. Older Adults - Heart Disease, Cancer
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Four Reasons for Age Associations
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1. Validity of Diagnosis 2. Multimodality 3. Latency Effects 4. Biologic Clock and Behavioral Phenomena
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Define: Multimodality
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...
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Define: Bimodal Distribution
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Graph with two distinct peaks.
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Define: Latency Effects
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1. Time period between onset of exposure to onset of clinical symptoms. (Textbook definition) - Definition 1 includes the Induction Period. - Epidemiologists usually use this definition. 2. Onset of pathogenesis to appearance of clinical symptoms.
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Define: Induction Period
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...
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Define: Morbidity
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The incidence of disease.
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Four Key Phrases from Epidemiology Definition
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1. Determinants 2. Distribution 3. Population 4. Health Phenomena/Problems
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Define: Determinants
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Factors that are capable of bringing about a change in health. Also known as "Risk Factors" or "Exposures"
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Define: Distribution
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Variation by age group, time, geographic location, etc.
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Population refers to....
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Groups of people, not separate individuals. The only time there's an exception is if it's an individual whose condition may affect the whole population. In this case, that person is a "determinant" or "Risk Factor"
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Three Aims of Epidemiology
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1. Describe the health status of a population. 2. Explain the etiology of disease. 3. Predict, Prevent, and Control health problems.
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Another word for Epidemiology
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"Popuation Medicine"
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Define: Epidemic
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The occurence in a community or region of cases of an illness clearly in *excess of expectancy*.
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What two things do you need to determine if an epidemic is present?
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1. Surveillance 2. Epidemic Threshold
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What's the difference between surveillance and surveying?
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Surveillance is ongoing, over a long period of time. Surveying is short, is often for a very specific reason.
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What does surveillance do?
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It allows us to determine what is "normal" or "regular" within a certain distribution. - It establishes a baseline.
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Define: Epidemic Threshold
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The minimum number of cases (or deaths) that would support the conclusion that an epidemic is underway.
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When can a single case of a disease constitute an epidemic?
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When the epidemic threshold is zero. - This occurs when a new disease is discovered or when a disease has been absent from a community for a long time (i.e. smallpox)
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Define: Endemic
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Habitual presence of a disease within a given geographic area.
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What's one important quality of an Endemic?
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It must remain below the Epidemic Threshold.
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Why is the WHO definition of pandemic different?
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The WHO definition says that the disease must be in "two or more countries in one WHO region and in at least one other country in another WHO region."
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How many WHO regions are there?
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Six 1. Americas 2. African 3. European 4. Eastern Mediterranean 5. Southeast Asia 6. Western Pacific
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Characteristics of the Black Death
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1. Bubonic Plague (the disease) 2. Claimed ¼ to ²/₃ European population. 3. Latest Plague outbreak - Peru (July 2010)
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1918 Influenza Pandemic is also known as?
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The Spanish Flu
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Characteristics of the 1918 Influenza Pandemic?
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1. Killed 50-100 Million people worldwide. 2. *2.5%* fatality rate compared to the 0.1% for other influenza pandemics.
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What is the latest pandemic?
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H1N1 (Swine Flu) in 2009
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What does a WHO Phase 6 (Pandemic) alert entail?
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Human to human transmission of an animal or human-animal influenza reassortant virus in two or more countries in one WHO region and at least one other country in another WHO region.
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What's the problem with the 2009 WHO Report on the H1N1 pandemic?
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1. Results only include those that were tested and lab-confirmed. 2. Countries should report to the WHO, but are not required to do so. - many cases went unreported.
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Significance of Hippocrates?
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1. Wrote, "On Airs, Waters, and Places." 2. Suggested that disease is associated with the physical environments; moved away from supernatural explanations of disease causation. 3. Father of Clinical Medicine 4. Hippocratic Oath
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Significane of John Graunt?
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1. Wrote, "Natural and Political Observations Made upon the Bills of Mortality." 2. Recorded seasonal variations in births and deaths. 3. Showed excess male over female differences in mortality. 4. Called the "Columbus of Biostatistics."
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Significance of John Snow?
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1. English Physician 2. Investigated Cholera outbreak in London. 3. Linked Cholera epidemic to contaminated water supplies. 4. Spot Map
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What does GIS stand for?
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Geographic Information System
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Snow's "Spot Map" is an early version of what Epidemiological technique?
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GIS = Geographic Information System
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Another name of Natural Experiment?
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Observation Study
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Difference between Observational Study Designs and Experimental Study Designs?
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In experimental study designs, determinants (risk factors/exposures) are manipulated.
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Example of an Experiment Study Design?
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Clinical Trial
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Define: Natural Experiment
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When an epidemiologist observe the changes in an outcome as the result of a naturally occurring situation. - Does not manipulate the determinants/exposures. - May be the result of legislation, policy changes, or environmental interventions.
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What are three Disappearing Disorders?
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1. Smallpox 2. Polio 3. Schistosomiasis japonica
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Characteristics of Residual Disorders
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1. Key contributing factors are largely known. 2. Methods of control not implemented effectively.
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Examples of Residual Disorders
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1. STDs 2. Health complications related to alcohol and tobacco use.
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Characteristics of Persisting Disorders
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1. No effective method of prevention or no known cure.
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Examples of Persisting Disorders
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1. Certain types of cancers 2. Mental Disorders
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Characteristics of New Epidemic Disorders
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1. Diseases that are increasing in frequency.
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Examples of New Epidemic Disorders
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1. New Influenza strains 2. Type II Diabetes
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Demographic Transition from Underdeveloped to Developed Countries
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High birth/death rates to low birth/death rates.
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Characteristics of Fixed Population
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1. There's no change in population size due to births or in-migration. 2. The only way that the population size can change is through *deaths.*
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Most common type of Population Dynamic (Choose: Fixed, Dynamic, or Steady)
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Answer: Dynamic Where the population size can increase through in-migration and births; can decrease through out-migration and deaths.
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Define: Steady Population
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When the number of births and in-migration is equal to the number of deaths and out-migration.
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Two major methods used in Health Services Research?
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1. Operations Research (OR) 2. Program Evaluation
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Significance of the Bradford Hill Criteria
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Some of the criteria are required before you can say a risk factor is a causal factor.
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Another name for the "Dose-Response Relationship"?
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Biological Gradient
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Another name for "Time Sequence"?
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Temporality
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Of the Bradford Hill Criteria, which ones are important?
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1. Strength of Association 2. Time Sequence (Temporality) 3. Consistency upon Repetition 4. Coherence of Explanation 5. Biological Gradient (Dose-Response)
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Define: Natural History of Disease
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Course of a disease from its beginning to its final clinical end point.
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What are the three major periods in the Natural History of Disease?
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1. Prepathogenesis 2. Pathogenesis 3. Outcome
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Pathogenesis is broken down into what two phases?
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1. Preclinical Phase 2. Clinical Phase
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When does the Preclinical Phase begin?
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The onset of disease, HOWEVER no signs or symptoms are present.
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When does the Clinical Phase begin?
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When signs and symptoms of the disease become visible.
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When does Primary Prevention occur?
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During Prepathogenesis, when an individual is healthy. Primary Prevention includes health promotion and specific protection against diseases.
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Two types of Primary Prevention?
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1. Active - Requires patient's behavioral change. - Ex: Condom use, Smoking cessation 2. Passive - Does *NOT* require patient's behavioral change. - Ex: Fluoridation of Public Water
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When does Secondary Prevention occur?
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During pathogenesis, but only during the preclinical phase (i.e. no symptoms) - Designed to reduce progress of the disease. - Early diagnosis and prompt treatment, - Ex: Screening programs (Cancer, Diabetes, HIV, BP)
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When does Tertiary Prevention occur?
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Pathogenesis; during the clinical (treatment) phase. - Designed to limit disability from disease. - Directed at restoring optimal functioning (Rehabilitation) - Ex: Physical Therapy, Fitness Programs.
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Define: Proportion
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A measure that states a count relative to the size of the larger group. - The numerator is part of the denominator. - May be expressed as a percentage - Can demonstrate the magnitude of a problem - Can be used to compare populations.
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Define: Rate
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An expression of the *frequency* with which an event occurs in a defined population in a *specific time period*.
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What three elements does a Rate include?
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1. Frequency of disease or death. 2. Unit size of the population 3. Time period during which the event occurs.
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Define: Prevalence
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The number of *existing* cases of a disease or health condition in a population at some designated time. - Allows use to measure the Burden of a health problem in a population - Allows us to determine the allocation of health resources.
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What does "existing" cases mean?
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Existing means "old plus new" cases.
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What are the three types of Prevalence?
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1. Point Prevalence 2. Period Prevalence 3. Lifetime Prevalence
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What is lifetime prevalence?
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A measurement of the people who had a disease at some point in their lives. - We don't know if they currently have it - Hard to specify the timer interval.
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Define: Incidence
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The number of *new* cases of a disease that occurs in a group during a certain time period.
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Difference between Prevalence and Incidence?
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Prevalence = Existing Cases (Old + New) Incidence = New Cases
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Two Types of Incidence
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1. Cumulative Incidence 2. Incidence Density
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Cumulative Incidence Characteristics
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1. Rate of development of a disease in a group over a certain period of time. - "The risk of developing a disease."
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Cumulative Incidence has Three Elements:
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1. Numerator = Number of new Cases 2. Denominator = Population at Risk 3. Time Period
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Another name for Incidence Density
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"Incidence Rate"
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Two alternative names for Cumulative Incidence
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1. Just Incidence 2. Incidence Proportion
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What happens with Prevalence and Incidence when the duration of a disease is short?
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Prevalence becomes similar to incidence.
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What causes a short duration?
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1. Quick Recovery 2. Fatality
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What happens with Prevalence and Incidence when the duration of a disease is long and incidence is low?
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1. Cases accumulate 2. Prevalence increases greatly to incidence.
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What does PMR stand for and whatt does it indicate?
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1. Proportional Mortality Ratio 2. Indicates the relative importance of a specific cause of death; not a measure of the risk of dying of a particular cause.
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What does CFR stand for and what does it indicate?
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1. Case-Fatality Rate 2. It's a measurement of the severity of the disease.
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Problem(s) with Crude Rates
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1. Might give rise to misleading conclusions if used to compare health status between populations. 2. Observed differences in crude rates may be the result of systematic factors.
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What is the most common rate adjustment made?
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Adjustment for Age
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What's the purpose of Adjusted Rates?
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1. To remove the effect of differences in the composition of various populations. 2. Allows unbiased comparison of morbidity and mortality rates between populations.
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Are Adjusted Rates considered Artificial Rates?
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Yes!
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Why are adjusted rates considered Artificial Rates?
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Crude rates have been converted into standardized rates. It's not the the exact number of observed cases, but they're numbers that allow us to compare different populations in an unbiased way.
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Two Methods to Calculated Adjusted Rates
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1. Direct Method 2. Indirect Method
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When do you use the Direct Method?
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1. When age-specific death rates are known. 2. A suitable standard population is available.
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When do you use the Indirect Method?
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1. When age-specific death rates are *unknown* or *unstable*.
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What is used with the Indirect Method?
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Standardized Mortality Ratio (SMR)
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Cause-Specific Rate
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(Number of deaths due to a disease)÷(Population size at midpoint of time period)
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Between which ages are women considered to be able to have children?
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15-44 years
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What is the requirement to be considered a fetal death
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Death must have occurred after 20 weeks or more of gestation.
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Which three equations are expressed as percentages?
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1. CFR - Case Fatality Rate 2. PMR - Proportional Mortality Ratio 3. SMR - Standardized Mortality Ratio
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What age is considered an infant?
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0 - 365 days.
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What's considered neonatal?
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Infants under 28 days old.
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What's considered Postneonatal?
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Infants between 28 and 365 days old.
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Whats considered Perinatal?
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28 weeks or more of gestation
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What's the purpose of Descriptive Study?
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1. Identify a health problem 2. Characterize the amount and distribution of disease 3. Formulate a hypothesis
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What's the purpose of Analytic Study?
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1. Follow Descriptive studies. 2. Identify the cause of the health problem. - Hypothesis testing.
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Which happens first: Descriptive Studies or Analytic Studies?
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Descriptive
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What are the six disease preventable by vaccination?
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1. Polio 2. Tetanus 3. Diphtheria 4. Tuberculosis 5. Measles 6. Pertussis
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Define: Latency
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The time between the infection and onset of symptoms.
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What are associated with the Biological Clock?
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1. Waning of the immune system - The immune system strengthening or weakening with age. 2. Aging - Conditions that require a trigger relating to age. Ex: Huntington's Disease
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Characteristics of Huntington's Disease
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1. Autosomal Recessive 2. Gene present from birth, but not activated until a specific age (usually around 30) - Emphasis here is the biological clock and human aging.
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Define: Female Paradox
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Females have higher morbidity rates than males, but lower mortality rates.
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What does CHD stand for?
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Coronary Heart Disease - Lower among women than men.
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What is a possible explanation for the Female Paradox?
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Women take their healthcare more seriously and visit their primary care physician more frequently. As a result, their morbidity rate is higher, but their mortality rate is lower.
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What is one possible explanation for women have a lower incidence of CHD?
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1. Production of Estrogen
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What are the two theories that try to explain why married people were found to be healthier?
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1. Protective Factor 2. Selective Factor
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Define: Protective Factor
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Married couples support and create an environment which is more conducive to good health.
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Define: Selective Factor
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People who marry may be happier to begin with. If you have better health, you're more likely to find a spouse.
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Characteristics of African Americans
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1. Higher mortality rate 2. Higher blood pressures. 3. Highest female breast cancer death rate.
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Characteristics of Native Americans
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1. TB rate twice that of the US population, 7 times that of whites.
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Characteristics of Pima Indians:
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Mortality rate many times that of all races in US for: 1. Accidents 2. Cirrhosis 3. Homicide 4. Suicide 5. Diabetes
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Characteristics of Asian Americans
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1. Lower rates of CHD and Cancer (linked to diet) 2. High Smoking Rates 3. TB Rates highest among Asian/Pacific Islander.
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Characteristics of Hispanics/Latinos
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1. Lower rates of CHD 2. Higher rates of diabetes - According to the San Antonio Heart Study.
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What is the, "Hispanic Mortality Paradox"?
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Although Hispanics as a group have lower Socio-Economic Statuses (SES), they have lower mortality rates than non-Hispanic white and blacks. Usually, lower SES means high mortality rates.
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Define: Salmon Bias Effect
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Hispanics come to the US as young children and return to their country of origin to die and their deaths are not recorded in the US.
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Define: Statistically Immortal
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The unrecorded deaths of Hispanics in the US because they return to their home country to die.
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What is the Antonio Heart Study?
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Study that found Mexican Americans to have a higher rate of diabetes.
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Define: Healthy Migrant Effect
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Healthier, younger persons usually form the majority of migrants.
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Define: Acculturation Hypothesis
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Immigrants' health profiles converge with that of native-born
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What type of studies are done to show Acculturation Hypothesis?
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Migrant Studies
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Three Variables of SES
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1. Occupation 2. Education 3. Income
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Urban diseases and mortality are associated with:
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1. Crowding 2. Pollution 3. Poverty
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Increased with decreasing urbanization are:
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1. Mortality 2. CVD Mortality 3. Poor health status 4. Lack of health insurance
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What are Localized Place Comparisons?
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Disease patterns due to unique environmental or social conditions found in a particular area of interest.
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What are two diseases associated to unique environmental conditions in a particular area of interest?
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1. Fluorosis - Associated with naturally occurring fluoride deposits in water. 2. Goiter - Iodine deficiency formerly found in land-locked areas of US.
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Reasons for Place Variation in Disease? (3)
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1. Gene/Environment Interaction 2. Influence of Climate 3. Environmental Factors
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Three Characteristics of Time
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1. Cyclic Fluctuations 2. Secular Time Trends 3. Clustering - Temporal - Spatial
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Define: Cyclic Fluctuation
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Increases and decreases in the frequency of diseases and health conditions over a period of a few years or within a year.
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Define: Secular Fluctuation
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Gradual changes in the frequency of a disease over a long periods of time.
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Two Types of Clustering
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1. Temporal Clustering 2. Spatial Clustering
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Define: Clustering
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An unusual aggregation of health events grouped together in time or space.
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Examples of Temporal Clustering
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Postpartum Depression; Post-Vaccination
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Examples of Spatial Clustering
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Concentration of disease in a specific geographic area. Ex: Hodgkin's Disease
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Define: Screening
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The presumptive identification of unrecognized (asymptomatic) disease, which can be applied rapidly. - Not intended to be a diagnostic
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Two types of Screening
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1. Mass/Universal Screening 2. Selective Screening
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When do we do screening?
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Preclinical phase; before symptoms appear.
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Define: Mass/Universal Screening
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When everybody in a population is screened regardless of the risk status. - General less expensive and easy to administer. Ex: Newborn hearing tests, Pap test for cervical cancer.
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Define: Selective Screening
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When a subset of the population at higher risk for disease is screened. - More economical - because you're screening less people, but generally the techniques are more expensive. Ex: Memmography screening for women under 40 with a family history of breast cancer.
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Characteristics of a Good Screening Tool (7)
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1. Accurate 2. Reliable 3. Simple 4. Rapid 5. Inexpensive 6. Safe 7. Acceptable
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Two Components of Validty
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1. Sensitivity 2. Specificity
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Define: Validity
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The ability of a measuring instrument to distinguish between who has the disease and who does not.
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Define: Sensitivity
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The ability to correctly identify those who have disease.
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Define: Specificity
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The ability to correctly identify those who do *NOT* have the disease.
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What is the "Gold Standard"?
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100% or almost 100% accurate tests. - Give us the truth about the disease status.
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True Prevalence
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(All Diseased)/(Total Population)
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Can a Gold Standard test be used as a Screening Test?
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Only if it has the characteristics of a good Screening Tool.
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When would you want to have high sensitivity?
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1. When penalty of associated with missing a case is high. - When disease is serious and treatment exists. - When disease can be spread - *When the diagnostic evaluation is associated with a minimal cost and risk*.
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When would you want to have high specificity?
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When cost or risk associated with further diagnostic testing is substantial.
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What are the two Predictive Values?
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1. Positive Predictive Value (PPV) 2. Negative Predictive Value (NPV)
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What does PPV tell us?
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What proportion of patients who test positive truly have the disease
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What does NPV tell us?
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What proportion of patients who test negative do NOT have the disease.
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Predictive Value is based on what three things?
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1. Sensitivity 2. Selectivity 3. Prevalence
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What kind of relationship is there between Positive Predictive Value and Prevalence?
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Positive Correlation
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What's another word for Reliability?
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Precision
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What is reliability?
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(Definition of Precision): The ability of a measuring instrument to give consistent results on repeated trials.
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What are the Types of Variation/Error involved in Reliability?
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1. Intraperson 2. Intraobserver 3. Interobserver (interjudge or interrater) 4. Instrument or Method
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Define: Intraperson Variation
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Using same test, method, technique on same person at two different times and getting different results. - Not because of the instrument, but because of the biological characteristics of that person. Ex: Blood pressure
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Define: Intraobserver Variation
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Same observer examining the same test results or performing the same test, but getting different results. Also known as, Human Error.
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Define: Interobserver Variation
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Disagreement on results based on two different observers.
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Can a test be valid but unreliable?
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No
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Can a test be highly reliable but invalid?
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Yes.
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Criteria for Effective Screening
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1. Condition must be serious. 2. Condition must be treatable. 3. Condition must be detectable while still asymptomatic and timely treatment must reduce morbidity and mortality. 4. Must be acceptable to the patient and inexpensive. 5. Condition must be sufficiently prevalent to warrant screening. 6. A relatively accurate screening test must be available.
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Three types of Bias?
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1. Volunteer Bias 2. Lead Time Bias 3. Length Biased Sampling
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Formulas to Know
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1. PPV 2. NPV 3. Sensitivity 4. Specificity 5. True Prevalence 6. SMR
