epi midterm
Outcomes of clinical trials
"clinical end points" can include rates of disease, death or recovery
Crude rate formula
(Number of deaths / total population) x 1000
Incidence Rate Formula
(Number of new cases in a given time period / Total population at risk in same time period) x 10^n
Prevalence Rate Formula
(Number of people with a disease at a given point in time / population at risk at the same point in time) x 10^n
Standardized Mortality Ratio (SMR)
(observed # of deaths per year) / (expected # of deaths per year)
Age-Adjusted Rates Formula
(observed deaths / observed populations) = x / standard population X = "expected" number of deaths for that stratum group
Strengths of clinical trials
- Provide the greatest control over: • amount of exposure • timing and frequency of exposure • period of observation - Ability to randomize reduces the likelihood that groups will differ significantly
Host factors
-Age, sex, ethnic group, nutritional status, socioeconomic status -Personal behaviors: smoking, diet, drinking, sexual practices, exercise -Immunization status: vaccination status physiological states: pregnancy, puberty, fatigue, immunocompromised, pre-existing disease
Limitations of clinical trials
-Artificial setting -Limited scope of potential impact -Adherence to protocol is difficult to enforce -Ethical dilemmas
Characteristics of clinical trials
-Carefully designed and rigidly enforced protocol -Tightly controlled in terms of eligibility, delivery of the intervention, and monitoring out outcomes -Duration ranges from days to years -Participation is generally restricted to a highly selected group of individuals. -Once subjects agree to participate they are randomly assigned to one of the study groups (e.g. intervention or control/placebo)
Retrospective cohort study
-Despite substantial benefits of prospective cohort studies, investigators have to wait for cases to accrue. -Retrospective cohort studies make use of historical data to determine exposure level at some baseline in the past. Advantages: -a significant amount of follow-up may be accrued in a relatively short period of time -the amount of exposure data collected can be quite extensive and available to the investigator at minimal cost
Advantages of prospective cohort studies
-Exposure measured before outcome has occurred -Enable the investigator to collect data on exposures; the most direct and specific test of the study hypothesis. -The size of the cohort is under greater control by the investigators. -Direct measures of the environment (e.g., indoor radon levels, electromagnetic field radiation, cigarette smoke concentration) can be made
crude rate vs age adjusted rate
-If the crude rate is higher before adjusting for age, then the study population is younger than the standard population -If the crude rate is lower before adjusting for age, then the study population is younger than the standard population -higher rates belongs to the older population
Disadvantages of case-control studies
-Provide indirect estimate of risk (odds ratio) -Timing of exposure-disease relationship difficult to determine -Representativeness of cases and controls often unknown -Data may be subject to reporting biases
Advantages of Retrospective Cohort Studies
-Reconstruct exposure data and outcome data -Make sure of previously-collected data to determine exposure level at some baseline in the past -Significant amount of follow-up may be accrued in relatively short period of time -the amount of exposure data collected can be quite extensive and available to the investigator at minimal cost
Advantages of case-control studies
-Tend to use smaller sample sizes than surveys or prospective studies -Quick and easy to complete -Cost effective -Useful for studies of rare diseases
Experimental Research
-Used to text effect of new treatments, tools, and programs to see if they prevent, cure, or slow the rate of disease -investigators manipulate study factor that affects disease -randomization of study subjects -"Gold Standard" of study designs -Randomized Control Trials (RCTs), field trials, and community interventions
Case control study characteristics
-a single point of observation (no follow-up) -unit of observation and unit of analysis are the individual -data collection typically involves combination of both primary and secondary data sources -study groups are defined by presence or absence of the outcome -exposure is determined retrospectively -does not directly provide incidence data (calculate OR)
Henle-Koch postulates are not relevant to many contemporary diseases
-agent present in every case of a disease -one agent - one disease, agent is not present in other disease -exposure of health subjects (animals) to agent will produce disease -agent can be recovered from the experimental animal
environment
-air pollution from stationary and mobile sources -access to open spaces/parks -availability of clean water -availability of healthy groceries compared to number of fast-food restaurants and liquor stores -nutritional quality of foods and beverages provided to school children
community infrastructure
-availability of social and health services -quality of housing -social stability
Defining cases
-clear and specific definition of diagnosis -incident vs. prevalence cases (incident generally preferred because not biased by duration of disease) -ideally, want to identify and enroll all incident cases in a defined population in a specified time period (not always practical)
Crude Rates (disadvantages)
-does not account for differences in population structure
Passive follow-up (follow-up issues)
-does not require direct contact with cohort members -possible when databases containing the outcomes of interest are collected and maintained by organizations outside the investigative term
Specific rates (advantages)
-examines subgroups -provides detailed information -can compare rates among subgroups
Cohort Baseline
-exposure status is known for all subjects -all subjects are free of the disease of interest -only take people in the study who do not have disease
Population pyramid: triangle population distribution
-high death rates from infections, high birth rates, and other conditions (developing)
High prevalence indicates...
-high incidence (lot of new cases) -long duration (people live a long time with the illness) -both
Availability of exposure data
-high quality historical exposure data are absolutely essential for retrospective cohort studies -need to trade off between a retrospective study design (with the benefits of more immediate follow-up time) and collection of primary exposure data in a prospective cohort design
health-related outcomes
-homicide/suicide rates -infant mortality rate -chronic and infectious diseases -drug and alcohol abuse rates -teen pregnancy rates -rates of sexually transmitted diseases -birth rate
Clinical data (data sources)
-hospitals -special clinics: not generalizable data due to highly selected group -physician practices: confidential, highly selected data, non-standardized
Factors that increase prevalence
-longer duration of the disease -survival without cure -increase in incidence -in-migration of cases -out-migration of healthy people -in-migration of susceptible people -improved diagnosis/reporting
Low prevalence indicates...
-low incidence (not a lot of cases) -short duration (cure or death) -both
Specific rates (disadvantages)
-may provide too much information -calculations can be tedious
Adjusted rates (disadvantages)
-not a "true rate" (adjusting to mimic the larger population) -hides differences between subgroups -comparisons are limited based on standard used -ability to calculate depends on information available
Strenghs of cohort studies
-permit direct determination of risk -time sequencing of exposure and outcome -can study multiple outcomes -can study rare exposures
Adjusted rates (advantages)
-provides a summary rate -controls for confounders -allows for comparisons between populations
Crude Rates (advantages)
-provides actual summary rates -easy to calculate
Factors the decrease prevalence
-shorter duration of disease -high case-fatality rate -decrease in incidence -out-migration of cases -in-migration of healthy people -out-migration of susceptible people -improved cure rate of cases
Limitations of cohort studies
-take a long time -costly -not ideal for rare outcomes -loss to follow-up common biases in cohort studies: -healthy worker effect -differential loss to follow-up
Population-based cohort studies
-the cohort includes either an entire population or a representative sample of the population -exposures unknown until the first period of observation when exposure information is collected-because you have defined your study population prior to assessing exposure level
Information required for a survival curve
-time of entry into the study -time of death or other outcome -status of patient at time of outcome
Explanation of observed changes in disease occurrence over time
-true change in disease occurrence -inconsistent interpretation and application of the case definition -change in the case definition -change in surveillance system/policy of reporting -change in population -random events -improved diagnosis
Observational Research
-used when experiment unethical or impractical -observe the natural exposure-disease relationship -no manipulation of study factor -includes case report, ecologic, cross-sectional, case control, nested case control, cohort study
Categories of non-communicable diseases
1. Congenital and hereditary 2. Allergies and inflammatory diseases 3. Degenerative diseases 4. Metabolic diseases 5. Cancer
Evaluation of community interventions
1. Formative: will all plans and procedures work as conceived? 2. Process: is the program serving the target group as planned? 3. Impact: has the program produced any changes among the target group? 4. Outcome: did the program accomplish its ultimate goal?
Three criteria for risk factors
1. The frequency of the disease varies by category or value of the factor (light smoker vs heavy smoker) 2. The risk factor precedes onset of the disease 3. The observation must not be due to error (ex:bias)
Seven Uses of Epidemiology
1. To study the history of the health of populations 2. To diagnose the health of the community 3. To study the working of health services-operations research 4. To estimate the individual risks of disease and other conditions, and the chances of avoiding them 5. To identify syndromes 6. To complete the clinical picture of chronic diseases 7. To search for causes of health and disease
Three approaches to descriptive epi
1. case reports 2. case series 3. cross-sectional studies
What are the 4 goals of epidemiology?
1. describe the distribution of disease (frequency, pattern) 2. explain etiology of a disease (causal factors, modes of transmission) 3. predict occurrence of a disease (estimate true frequency and distribution of cases) 4. control distribution of a disease (prevent new cases, eradicate existing cases, prolong lives)
Four Trends in Disorders
1. disappearing 2. residual 3. persisting 4. new epidemic
Stages of disease process
1. stage of susceptibility -exposure 2. stage of pre-symptomatic disease / subclinical disease 3. stage of clinical disease -onset of symptoms 4. stage of recovery, disability, or death
Analytical epidemiology
A means for identifying and quantifying associations -Testing hypotheses -Generating new or more specific hypotheses -Inferring about causality -Explains why and how health-related states or events occur
Cohort (generation) life table
A type of life table tabulating the year-to-year death rates for a group (cohort) of individuals born around the same time (e.g. same year).
Epidemiology can involve the study of: Infectious disease Chronic diseases Accidents and injuries A and B ONLY A, B, and C
A, B, and C
Which of the following might be considered an epidemic? Thousands of cases of Ebola in West Africa 2 cases of small pox in New Jersey 100 or more cases of meningitis in a Rutgers dorm A and C ONLY A, B, and C
A, B, and C
Characteristics of persons
Age Sex/Gender Marital Status Race and ethnicity Nativity and migration Religion Socioeconomic status
Which factors are those due to person, place, or time? Age? Race? Country of Origin? Rural or Urban Residence? Secular Trends?
Age: Person Race: Person Country of Origin: Person [Country of origin is similar to nationality, hence why it falls under person INSTEAD of place] Rural or Urban Residence: Place Secular Trends: Time
An observed increase of colorectal cancer incidence over time may be due to: Improved screening and diagnostic tests Changes in screening recommendations A true increase in colorectal cancer incidence All of the above
All of the above
Which of the following characteristics are required for a useful surveillance system? Systematic data collection Ongoing data collection Data analysis and interpretation Dissemination of data to improve public health practice All of the above None of the above
All of the above
describe characteristics that distinguish epidemic from pandemic
An epidemic is when there's an outbreak or cases of an illness that is of normal expectancy. There's an epidemic threshold where there's a minimum number of cases or deaths that would conclude there is an epidemic occurring. A pandemic is an epidemic on a worldwide scale where the disease may cross international borders.
Screening surveys (data sources)
Are done as needed -clientele are highly selected --> typically non-generalizable due to non-representativeness -multiphasic screening: giving 2 or more screening tests during a single screening program
Things to consider when conducting cohort studies
Availability of exposure data Size and cost of the cohort used Data collection and data management Follow-up issues Sufficiency of scientific justification
Descriptive epidemiology characterizes the amount and distribution of disease within a population and enables the researcher to... Make direct tests of etiologic hypotheses Generate testable hypotheses regarding etiology Evaluate trends in health and disease within a population B and C only A, B, and C
B and C only
Limitations of ecological studies
Cannot illustrate dose-response relationship as data represents average exposure, NOT individual exposure Cannot calculate a true measure of association as there is no real comparison group, especially unexposed cases Cannot adequately control for potential confounders/bias Cannot infer causal association as temporality highly questionable since data is not at the individual level
Nested case-control studies (special types of case-control studies)
Case-control studies in which cases and controls are drawn from an existing cohort -controls are selected from a list of cohort members who were at risk for becoming a risk for becoming a case at the time each case diagnosis occurs
Selecting cases
Census vs. sampled cases -census (all cases) is representative of case population, but may not be feasible -sampling methods are faster and less expensive, but cases must be drawn randomly in order to be representative
Descriptive Epidemiology
Characterizing the distribution of health-related states or events -Necessary for determining "expected" disease frequency -Key role in hypothesis development -Determines "who, what, and where"
Strengths of ecological studies
Conducted at the group level, typically using readily available data May help identify high-risk populations for prevention efforts May generate hypotheses for analytic studies
Subjects serve as their own control in which type of intervention study? Cross-over Run-in Factorial Matched pair randomization
Cross-over
Characteristics of time
Cyclic fluctuations Common source epidemics/Point epidemics Secular time trends Clustering Temporal clustering Spatial clustering
influence of population dynamics on health
Demographic transition: shift from high birth and death rates in Agrarian societies to lower birth and death rates found in developed countries Epidemiologic transition: shift in the pattern of morbidity and mortality from infectious and communicable disease to chronic, degenerative diseases
Key aspects of epidemiology
Determinants - factors or events that are capable of bringing about a change in health (biological agents, chemical agents, less specific risk factors) Distribution - frequency of disease occurrence may vary form one population group to another Population - epi examines disease occurrence among population groups, not individuals Health phenomena - epi investigates many different kinds of health outcomes Morbidity and mortality
Sufficient
Disease D may occur due to exposure E, but there are other factors which may cause disease D -need a host of factors
Which of the following is a characteristic of a case-control study? Diseased and no diseased individuals compared with respect to prior exposures Exposed and nonexposed individuals compared with respect to incidents of outcomes Exposure and disease status of individuals captured for the same time Based on aggregate level data Exposures assigned to study subjects (usually randomly) as part of the study protocol
Diseased and no diseased individuals compared with respect to prior exposures
New epidemic disorders
Diseases that are increasing in frequency examples: certain cancers, AIDs, obesity, type 2 diabetes, COVID-19 The emergence of new epidemics may be a result of: Increased life expectancy of the population new environmental exposures changes in lifestyle, diet and other practices
passive primary prevention
Does not require behavior change -Vitamin fortified foods -Fluoridation of public water supplies (generally easier because people aren't asked to change their behavior)
Hierarchy of Controls
Elimination - physically remove hazard Substitution - replace the hazard Engineering Controls - isolate people from the hazard Administrative Controls - change the way people work PPE - protect the worker
We discussed seven uses of epidemiology, grouped under two headings: (1) health status and health services, and (2) disease etiology. Which if the following types of studies fall under the study of disease etiology grouping? Estimate individual risks and chances Complete the clinical picture Diagnose the health of the community Study history of the health of populations Search for causes
Estimate individual risks and chances Complete the clinical picture Search for Causes
In ______ studies, the investigator introduces or withholds an exposure in order to determine its effects and randomizes participants. In _____ studies, subjects are studied under natural circumstances; participants are not assigned to exposure. Experimental, observational Observational, experimental Descriptive, analytical Analytical, descriptive
Experimental, observational
Which of the following is a characteristic of a cohort study? Diseased and no diseased individuals compared with respect to prior exposures Exposed and nonexposed individuals compared with respect to incidents of outcomes Exposure and disease status of individuals captured for the same time Based on aggregate level data Exposures assigned to study subjects (usually randomly) as part of the study protocol
Exposed and nonexposed individuals compared with respect to incidents of outcomes
Which of the following is a characteristic of an experimental study? Diseased and no diseased individuals compared with respect to prior exposures Exposed and nonexposed individuals compared with respect to incidents of outcomes Exposure and disease status of individuals captured for the same time Based on aggregate level data Exposures assigned to study subjects (usually randomly) as part of the study protocol
Exposures assigned to study subjects (usually randomly) as part of the study protocol
Assuming that the sample population is representative of the study population, and you would like to apply the findings of this study to all people in the UK (from where the participants were selected), what would need to be assured? You can select more than one. Internal validity External validity Generalizability Transportability
External validity Generalizability
Infectious disease epidemiology is really the only type of epidemiology True False
False (Epidemiology helps us understand more than just infectious diseases: the health between us and the environment (e.g., radon); chronic disease, lifestyle and health promotion (e.g., alcohol and liver disease); psychological and social factors in health (e.g., distribution and determinants of mental disorders); molecular and genetic epiemiology (e.g., BRCA1/2 gene in lung cancer), and more.)
The underlying premise in epidemiology is that disease or health related states are randomly distributed in populations. True False
False (Epidemiology is concerned with the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations. From the text, page 13: "Distribution relates to differences in disease patterns in subgroups of the population. The frequency of disease occurrence..vary from one population to another in the US")
Subjects for an exposure-based cohort study would be selected most appropriately from: Firefighters who respond to emergency calls by putting on heavy protective suit, and thus may develop fatigue during the emergency response Residents of New Jersey Female Rutgers alumni from 1950 to 2020 All of the above
Firefighters who respond to emergency calls by putting on heavy protective suit, and thus may develop fatigue during the emergency response
Necessary
For disease "D" to occur, the individual must be exposed to Agent "E" -in order for disease to occur, you HAVE to have exposure ex: Down's Syndrome NEEDS trisomy 21
Example of Population-based cohort studies
Framingham Study (used to study coronary heart disease) -Framingham, MA -ongoing study of CHD initiated in 1948 - used a random sample of 6,500 from targeted age range of 30 to 59 years
The definition of epidemiology includes the term "distribution." Which TWO of the following best describes this term? Frequency Determinants Population Pattern
Frequency, Pattern
Experimental studies
GOLD STANDARD manipulation of study factors (exposure) and randomization of subjects
Reasons for place variation in disease
Gene/environment interaction Influence of climate Environmental factors
Period (current) life table
Gives an overview of the present mortality experience of a population and shows projections of future mortality experience
To safely achieve _________ against COVID-19, a substantial proportion of a population would need to be vaccinated, lowering the overall amount of virus able to spread in the whole population. One of the aims with working towards this goal is to keep vulnerable groups who cannot get vaccinated (e.g. due to health conditions like allergic reactions to the vaccine) safe and protected from the disease.
Herd immunity Tertiary prevention Secondary prevention Active immunity None of the above
Case population sources
How can we identify our ideal case population? -a tumor registry or vital statistics bureau may provide a complete listing of all cases -medical facilities also may be a source of cases...but not always incident cases and may not be representative of the general population of those with the disease
Case-Control Study Example
If we are interested in examining whether lung cancer is associated with smoking: -identify a group of people with lung cancer CASES -identify a similar group without lung cancer CONTROLS -ask cases if they ever smoked CASE EXPOSURE -ask controls if they ever smoked CONTROL EXPOSURE If lung cancer is associated with smoking, then we would expect that more cases than controls will report a history of smoking
What is the primary advantage of setting strict inclusion criteria for a randomized clinical trial? Improve external validity Improve internal validity Reduce placebo effect All of the above
Improve internal validity
The Rotterdam Study is a prospective cohort study, which started in 1990. All inhabitants in Rotterdam age 55 and above (n = 10,275) were invited to participate and 78% (n = 7,983) participated. Individuals were interviewed at home and most (n =7,151) were examined at a research facility to collect baseline data, including an echocardiogram (ECG) which measures heart function. ECGs were available for analysis on 6,808 participants. 376 cases out of 6,808 participants (5.5 % of the study population) had heart abnormalities (HA) at baseline. Eligible study participants were followed-up and assessed through December 1999. After follow-up, 437 new HA cases per 44,175 person-years were identified (9.9 per 1,000 person-years). What is the name of this type of measure (9.9 HA per 1,000 person-years)? Incidence Density Cumulative Incidence Proportionate Morbidity Prevalence
Incidence Density
Limitations of community trials
Inferior to clinical trials due to lack of control over entrance into the study, delivery of the intervention and monitoring outcomes -Less-controlled --> not in a clinical setting Fewer study units are capable of being randomized, which affects comparability -Harder to randomize -Picking a control is difficult Affected by population dynamics, secular trends, and nonintervention influences
Clinical Trials
Investigational studies that test the usefulness of drugs or treatments
Exposured-based cohort studies
Made up of subjects with a common exposure ex: workers exposed to lead during batter production -overcome limitations of population-based cohort studies, which are not efficient for rare exposures -certain groups, such as occupational groups, may have higher exposures than the general population to specific hazards
Limitations of cross-sectional studies
No temporality *can never infer causality from cross-sectional designs* cannot calculate disease incidence, only prevalence not good for studying rare or deadly diseases limited usefulness for inferring disease etiology
Case-crossover studies (special types of case-control studies)
Only cases -compare exposures for "case time" vs. "control time"
Phases of clinical trials
Phase I Studies (clinical pharmacologic studies) Phase II Studies (efficacy studies) Phase III Studies (effectiveness studies) Phase IV Studies (post-marketing clinical trials)
Environment factors
Physical -weather -climate -geology Biological -sources of food, water, and air -presence of vectors, flora, and fauna Social and cultural -adequate housing -war -sanitation -access to health care
Wade Hampton Frost
Popularized cohort analysis method. Arranged tuberculosis mortality rates in a table with age on one axis and year of death on the other. One can quickly see the age-specific mortality for each of the available years on one axis and the time trend for each age group on the other.
Which type of prevention is achieved in this scenario: The US Housing and Urban Development Department has achieved something spectacular. Through their efforts, and with the help of policymakers, have passed a mandate to remove all lead-paint chips and asbestos from every house across the US. Primary Secondary Tertiary Quaternary This isn't a type of prevention
Primary
Cohort Studies: Timing of Data Collection
Prospective Retrospective Historical
Advantages of nested case-control studies
Provide a degree of control over confounding factors. Reduce cost because exposure information is collected from a subset of the cohort only. Usually allows for the study of additional outcomes and additional exposures (data permitting)
Case-Control Studies
Rare diseases Quick and inexpensive Examine multiple risk factors for a single disease Minimizes bias in the outcome determination Indirect estimate of risk Well-suited to the evaluation of diseases with long latency period *Uses Odds Ratio
Cohort Studies
Rare exposure Time-consuming and expensive Examine multiple effects of a single exposure Minimizes bias in the exposure determination Direct measurements of incidence of the disease Not ideal for diseases with long latency *Uses SMR
What are cohort studies good for?
Rare exposures (can identify a group who has exposure) Diseases with short latency periods (diseases that develop quickly)
What is not true about John Snow and the Cholera outbreak on Broad St. in London, August 19 to September 30, 1849 Removing the Broad St. water pump led to the largest decrease in incidence cases This was one of the first instances of an observational study. John Snow utilized a comparative group of individuals, determining that one of the greatest risk factor for disease was the Broad St. pump The going theory of disease etiology was of "miasma" or bad air. One of the first individuals to map out the frequency and distribution of infectious disease
Removing the Broad St. water pump led to the largest decrease in incidence cases
Strengths of community trials
Represent the only way to estimate directly the impact of change in behavior or modifiable exposure on the incidence of disease
Active primary prevention
Requires behavior change on part of subject -Wearing protective devices -Health promotion -Lifestyle changes -Community health education -Ensuring healthy conditions at home, school, and workplace
Tuberculosis Outbreak in a Long-Term-Care Facility for Mentally Ill Persons — Puerto Rico, 2010-2012 During January 2012, the Puerto Rico Department of Health (PRDOH) detected a tuberculosis (TB) outbreak among residents of a long-term-care facility in the San Juan metropolitan area. The same rare Mycobacterium tuberculosis genotype was identified in isolates from four patients. This facility housed 40 men, aged 40-71 years, with severe mental illness. During April 2012, CDC assisted PRDOH with the investigation to describe outbreak epidemiology, identify and prioritize contacts for evaluation and treatment, and provide recommendations on interventions aimed at stopping TB transmission.... Since the initial case was identified in July 2010, tuberculin skin tests were administered to 187 contacts during 2010-2012; 26 (81%) of 32 residents and seven (5%) of 155 nonresident contacts (facility employees and residents' family members) had evidence of latent TB infection. Administration of the tuberculin skin tests to identify individuals with latent TB infection (i.e., infection without symptoms), is which type of prevention measure? Primary Secondary Tertiary Quaternary This isn't a type of prevention
Secondary
Cohort Studies
Starts with a group of subjects who do not have the disease, but are at risk of the disease/outcome (going from cause to effect)
Cross-over designs
Subjects serve as their own controls in which type of intervention study -can be planned or unplanned -removes patient effect, variability, and increase precision -possible carry-over effect
Patients with chronic pain are often referred to a pain clinic to manage their pain. Which type of prevention measure is this? Primary Secondary Tertiary Herd Immunity This isn't a type of prevention
Tertiary
Phase I Studies (clinical pharmacologic studies)
Test new drug treatment in a small group of people (e.g. 20 - 80) for the first time to evaluate safety -determine levels of toxicity, metabolism, pharmacologic effect, and safe dosage range -identify side effects
Phase III studies (effectiveness studies)
The drug treatment is given to a large group of people (e.g. 1,000 - 3,000) to confirm effectiveness, compare it to standard treatments, and monitor side effects.
Phase II studies (efficacy studies)
The drug treatment is given to a larger group of people (e.g. 100 - 300) for efficacy and to further evaluate safety
Phase IV studies (post-marketing clinical trials)
The drug treatment is monitored to gather more information on risks, benefits and optimal use.
Select all the factors which help epidemiologists to determine the most appropriate study design for evaluation a particular association. The hypothesis being tested The state of knowledge on the topic The political support for the investigation Ethics and feasibility
The hypothesis being tested The state of knowledge on the topic Ethics and feasibility
Epidemiology
The study of the distribution and determinants of health-related states or events in specified population and application of this study to prevent and control health problems.
Sufficiency of Scientific Justification
There should be considerable scientific rationale for a cohort study Additional justification for cohort studies may come from laboratory experiments or animal studies Cohort studies are the only observational study design that permits examination of multiple outcomes
Big Data
Three V's -high variety -high volume -high velocity
Water-borne infectious disease continues to be a major source of morbidity and mortality globally. Which of the following is NOT a surveillance method used by public health agencies to reduce the incidence of gastrointestinal illness associated with drinking water? [Hint: remember that surveillance is epidemiology!] Surveillance of gastrointestinal illness and death in the general population Treating affected patients with antibiotics to reduce symptoms Testing of drinking water sources for microbial contamination Mapping gastrointestinal disease rates to correlate with drinking water source
Treating affected patients with antibiotics to reduce symptoms
Characteristics of place
Types of place comparisons: International Geographic (within-country) variations Urban/rural differences Localized occurrence of disease
Community Trials
Unit of analysis: group An experimental study where one group of people or community receives an intervention Limits the focus on the type of interventions that is possible Less rigid, cannot exert control Duration ranges- longer duration
Clinical trials
Unit of analysis: individual Usually controlled in terms of eligibility, delivery of the intervention and monitoring of outcomes Duration - days to years Restricted participation
Specific Rates
Used for certain subgroups of a population
Adjusted Rates
Used to remove effects of differences in composition of various population
Active Immunity
Where the body produces its own antibodies in response to -vaccine -having a specific disease pathogen in the body
Agent factors
a microorganisim, chemical, nutritive element or physical factor whose presence or absence is essential for a particular disease or condition to occur can include: bacteria, virus, protozoa, parasite
Ecological Studies
a type of investigation in which groups are compared without having information on the individuals within the group -cost effective because using data that already exists -not individual level data -no cases and controls --> no comparison groups
Pathogenicity (infectious diseases)
ability to cause clinical illness in infected host
Virulence (infectious diseases)
ability to cause severe illness or death
Infectivity (infectious diseases)
ability to infect a susceptible host
Population dynamics: open "dynamic" populations
adds new members through immigration and births or loses members through emigration and deaths -not a fixed group -number can change at any point in time ex: population of a country, city, or states in the United States
Population dynamics: closed "fixed" populations
adds no new members (cohort), and decreases in size due to deaths only ex: survivors of 9/11, hurricane katrina
Pathogenesis
after agent reacts with host
Components of Epidemiology Triangle
agent, host, environment
National Center for Health Statistics (NCHS) [data sources]
all births & deaths reported to local health dept --> state registrar --> federal level (NCHS) -vital statistics data
Passive immunity
antibodies produced by another person or animal -transplacental (mother to baby) -nursing
Prepathogenesis
before agent reacts with host
Allergies and inflammatory disease
body reacting to an invasion of or injury by a foreign object or substance (lupus, eczema)
Point (time trends)
brief increases
Analytic Studies (Observational)
causal associations, can prove causal relationships
Metabolic diseases
cause the dysfunction, poor function, or malfunction of certain organs or physiological processes within the body leading to disease states (hyperthyroidism, diabetes)
Disease registry (data sources)
centralized database for the collection of disease data -patient tracking: link disease registry to vital statistics -estimate incidence of disease -case-control studies -SEER program: collects cancer incidence, treatment, and survival from different cancer registries across the US
Cancer
characterized by abnormal growth of cells that form a variety of tumors, both benign and malignant
Morbidity surveys (data sources)
collects data about the health status of a population group; more comprehensive due to taking clinical measurements and survey -NHANES: collects clinical measurements via clinical examination -NHIS: household survey of US noninstitutionalized persons; collects data on diseases, injuries, disabilities, risk behaviors -BRFSS: largest telephone survey in the world --> collects data on behaviorally related phenomena
Disappearing Disorders
conditions that were once common but are no longer present in epidemic form examples: smallpox, polio, measles
Primordial prevention
creation of healthy living and social conditions
Relative Risk (RR)
cumulative incidence in exposed/cumulative incidence in unexposed
Descriptive Studies (Observational)
describe populations, can't prove causality with them
Degenerative diseases
deterioration of body systems, tissue, and functions (Parkinson's, MS)
Community intervention trials
determine the potential benefit of new policies and programs a quasi-experimental design
Active follow-up (follow-up issues)
direct contact by investigator by mailings, phone calls, or written invitations to return to study sites/centers
Residual Disorders
diseases for which the key contributing factors are largely known but specific methods of control have not been effectively implemented examples: STDs, tobacco use, infant mortality
Persistent disorders
diseases for which there is no effective method of prevention or no known cure examples: certain cancers and mental disorders
Prophylactic Trial
evaluates the effectiveness of a substance that is used to prevent disease; it can also involve a prevention program.
congenital and hereditary diseases
familial tendencies toward certain inborn abnormalities within families (Type 1 diabetes, Alzheimer's)
Life Table methods
give estimates for survival during time intervals and present the cumulative survival probability at the end of the interval
Strengths of cross-sectional studies
good method for identifying prevalence of common diseases describe magnitude of health problem generate hypothesis about various risk factors/exposures and disease outcome
Secular (time trends)
gradual changes in the frequency of disease over long time periods
reportable disease statistics (data sources)
healthcare providers reporting classified disease required by federal & state statutes
School health programs (data sources)
immunization data, screening data, sports physical exams, absentee data
Rate Ratio (RR)
incidence rate in exposed/incidence rate in unexposed (more precise)
Unit of analysis for cohort studies
individual
Population pyramid: rectangle population distribution
infection takes a smaller toll and takes a smaller percentage of people (developed)
Population in equilibrium or steady state
influence of births, deaths, and migration do not contribute to net increases or decreases in the number of persons population number is constant
U.S. census (data sources)
info about entire US population --> demographic variables
Therapeutic Trial
involves the study of curative drugs or a new surgical procedure to improve the patient's health
Rate
measure of the frequency with which an event occurs in a defined population over a specified period of time - a proportion with the specification of time included
Morbidity data from armed forced (data sources)
morbidity, physical exams, military medical records
Direct Method (adjusting rates)
need age-specific rates of morbidity and mortality of group
Insurance data (data sources)
only includes sample of population with insurance -social security: data on recipients of disability benefits and Medicare -life insurance: data on mortality and results from physical exams -health insurance: data on recipients in prepaid medical program
Pathogens (infectious diseases)
organisms or substances that are capable of producing disease ex: prions, bacteria, viruses, fungi, parasites, etc.
Cyclical (time trends)
periodic changes in the frequency of diseases and health conditions over time
Specific prevention
personal protective devices for workers, vaccinations for vaccine-preventable diseases
Absenteeism data (data sources)
records of absenteeism from school or work; useful for study of rapidly spreading conditions
Generalizability vs. validity
restricting study population can help control for certain confounders (improve validity) but yields a less representative population (decrease generalizability)
Bradford Hill Criteria
strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, analogy
Efficiency
the effect or end results achieved in relation to effort expended (e.g. money, resources, and/or time)
Effectiveness
the extent to which a specific intervention produces intended effects for specific population in practice
Efficacy
the extent to which an intervention does more good than harm under ideal circumstances
Randomization
the method of choice for assigning subjects to the treatment or control conditions of a clinical trial or intervention
Population decrease in size
the number of persons emigrating plus the number of deaths exceeds the number of persons immigrating plus the number of births
Population increase in size
the number of persons immigrating plus the number of births exceeds the number of persons emigrating plus the number of deaths
Prevalence
the proportion of susceptible population with a disease or condition -describes burden of illness in a population -guides allocation of resources -can help estimate the frequency of an exposure -outcome measures often expressed as a power of 10 (10^n)
Case control study
to examine the possible relation of an EXPOSURE to a certain disease, we identify a group of individuals with that disease and a group of people without that disease for consumption -one group has the disease of interest (cases) -a comparable group is free from the disease (controls) Investigate whether certain past experiences or exposures are more or less probable among cases than controls -we determine what proportion of the cases were exposed and what proportion were not exposed -we also determine what proportion of the controls were exposed and what proportion were not exposed *In case-control studies, the outcome is always identified prior to the exposure* -identify cases (persons with outcome of interest) -identify controls (similar except not cases) -go back in time to see what proportion of each group was exposed to a potential risk factor
Case-control studies
to examine the possible relation of an exposure to a certain disease, we identify a group of individuals with that disease and a group of people without that disease for comparison unit of analysis: individual *does not directly provide incidence data*
Cross-Sectional Studies
unit of observation = individual simultaneously measure disease and exposure
Clustering (time trends)
unusual aggregation of health events grouped together in space and time -temporal clustering (ex: post-vaccination reactions) -spatial clustering (concentration of disease in a specific geographic area
Indirect Method (adjusting rates)
used if age-specific death rates of the population for each standardization are unknown or unstable -need population age breakdown
