Public Health Research And Practice Exam 1

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The Public Health Model

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1. Define the problem
2. Identify risk and protective factors
3. Develop and test prevention strategies
4. Assure widespread adoption

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Descriptive Epidemiology

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Person, place, and time
-the who/what/when/where/why/how

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FINER

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Feasible
Interesting
Novel
Ethical
Relevant

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Types of study designs

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descriptive; observational; quasi-experimental; experimental

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Descriptive studies

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correlational/ecological
focus groups
cross-sectional

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observational studies

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case-control
cohort

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quasi-experimental studies

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-pre-test/post-test with external controls
-pre-test/post test without external controls

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experimental studies

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-randomized controlled trial
-group randomized control trial
GOLD STANDARD

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correlation study (type of descriptive study)

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Correlates disease rates with specific characteristics based on aggregated data within or across populations
-can be completed quickly and inexpensively and used to generate etiologic hypotheses
-cannot test etiologic hypotheses or determine causality

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ecological fallacy

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inappropriate conclusions regarding exposure-disease relationships at the individual level that are based on aggregate data

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Case Studies (type of descriptive study)

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- case report: detailed clinical description of the characteristics of a new disease or impaired condition of a single patient.
- case series: a collection of case reports that focus on patients with the same disease or impaired condition
-can be used to detect emergence or new diseases/epidemics and generate etiologic hypotheses
-cannot be used to test hypotheses
--> no comparison population!

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Focus group (type of descriptive study)

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small group asked about perceptions, beliefs, and experiences on some matter
qualitative
generate etiologic hypotheses but no causation!

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2 x 2 table

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outcome
exposed yes no
yes
no

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cross sectional study (type of descriptive study)

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-looks at exposures and outcomes simultaneously
-cannot determine causality, but only if there is a positive or negative correlation between two factors
-Young Men's Survey (MSM)

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case-control study (type of observational study)

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-retrospective (know outcome, looking for exposure)
-used when outcome is rare
-select cases and controls
-determine exposure
-can determine causality, though at risk for bias

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cohort study (type of observational study)

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-prospective (create exposure--> looking at outcome)
-can look at multiple exposures
-select population at risk and follow to see if outcome occurs
-can determine causality, but biased!
-CHOICE project

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Randomized control trial

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-prospective (give exposure, look for outcome)
-select population at risk and RANDOMIZE exposure to intervention (i.e. have a control group and and exposure group that are similar in nature and give one exposure and one placebo and look at effect)
-can determine causality, and random assignment controls for bias!

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epidemiology

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The comparative study of the distribution and determinants of disease in human populations

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descriptive epidemiology

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distribution or patterns of disease within or across defined populations

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analytic epidemiology

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determinants or factors that influence the prevention, occurrence, control, and outcome of disease

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Prevalence

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Prevalence is the number of existing cases of disease in the population at any given time (point, period, lifetime prevalences often determined)
-prevalence ~ incidence rate x duration of diseaseper

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incidence

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the number of new cases of disease that develop in a the population during a defined period

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person-time

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estimate of the time that an individual contributed to/was a part of a dynamic population
how to compute:
-count the person time contributed by each person in the population during the study period [preferred]
-multiply the average size of the population at the mid-point of the study times the duration of the study period

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incidence density/rate

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measures the rate at which new cases of disease occur in the population at risk during a defined period

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cumulative incidence

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measures the proportion of individuals in the population who develop the disease within a defined period

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crude rate

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estimate the actual disease frequency for an entire population

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category specific rates

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crude rates for subgroups of the total population
example: gender- or age- specific rates

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adjusted/standardized rates

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computed in order to remove the effect or age or other factors from crude rates to allow meaningful comparisons across populations when age distributions are different for the populations being compared

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Odds ratio

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-an estimate of the odds of disease in the exposed group relative to those who are not exposed
-when prevalence is <10% OR is good
-measures the strength or magnitude of the exposure-disease relationship
-use for a case control only
-if OR = 1, then there is no association between the exposure and disease status based on the data presented in the study

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relative risk

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-an estimate of the risk of developing the disease in the exposed group relative to those who are not exposed
-If you follow people over time you can calculate their risk
-cohort study, randomized control trail
-=(cumulative incidence of exposed)/(cumulative incidence of unexposed)
-if RR = 1, then there is no association between the exposure and disease status based on the data presented in the study

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attributable risk

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estimate of the excess risk of disease in the exposed population that is attributable to the exposure
-if AR = 0, then the incidence rates in exposed and unexposed populations are equal

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attributable risk percent

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estimate of the proportion of disease among the exposed population that is attributable to the exposure

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population attributable risk

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-estimate of the excess risk of the disease in the total population that is attributable to the exposure
-determines which exposures have the most relevance to the health of a community

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population attributable risk percent

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estimate of the proportion of disease in the total population that is attributable to the exposure

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P-Value

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-The probability of an effect as large or larger than the observed effect, assuming the null hypothesis is true
-null hypothesis is always that there is no association!!
-measures the strength of the evidence against the null hypotheses--> small p-values indicate stronger evidence against the null (i.e. that there is an association)
-p-values of <0.05 are generally accepted as statistically significant

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confidence interval

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-range surrounding the RR or OR
-can be 90, 95, or 99% confidence intervals
-if the interval does not include the value for no association then reject the Ho!
-(for OR or RR this value is 1.0, for AR this value is 0.0)

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Hill Criteria

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-outlines the minimal information needed to prove a causal relationship between two variables
-includes: time sequence, strength of association, biologic gradient, consistency upon repetition, plausibility, coherence of explanation, specificity analogy, experiment

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time sequence (hill criteria)

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-exposure precedes development of disease by a period consistent with proposed biologic mechanism
-sufficient induction/latent period exists

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strength of association (hill criteria)

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-stronger the association, the more likely the exposure-disease relationship is causal
-strong association is less likely than we weak association to be due to confounding bias

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biologic gradient (hill criteria)

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-aka dose-response
-strength of association increases with intensity or duration of exposure, as predicted

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consistency upon repetition (hill criteria)

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-other studies using different population and methodology show similar results

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plausibility (hill criteria)

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there are known or postulated biological mechanisms that help explain exposure-disease relationships

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coherence of explanation (hill criteria)

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association must not seriously conflict with what is already known about natural history or biology of disease

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specificity (hill criteria)

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-a specific exposure is associated with only one disease
-not necessarily applicable to chronic diseases --> specific exposure may be associated with multiple diseases

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experiment (hill criteria)

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-natural experiments provide evidence for exposure-disease relationships
-rarely available for human populations

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surveillance

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the ongoing collection and timely analysis, interpretation, and communication of health information for public health action

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Steps in planning a surveillance system:

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1. establish objectives
2. develop case definitions
3. determine data source or data-collection mechanism
4. develop data collection instruments
5. field test methods
6. develop analytic approach
7. develop dissemination mechanism
8. evaluate surveillance system

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Health Disparities

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Differential morbidity, mortality, and health-related well-being and quality of life among health populations

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Health Equity

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-assurance that all members of society have the opportunity for health -- a sense of well-being and the ability to lead full, productive lives regardless of SES, race/ethnicity, gender, sexual orientation or other social factors that might contribute to inequity

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Top four infectious diseases (highest mortality)

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1. lower respiratory infection
2. diarrhoeal diseases
3. HIV/AIDS
4. TB

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endemic

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habitual presence of a disease within a given geographical area

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epidemic

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occurrence in a community or region of a group of illnesses of similar nature, clearly in excess of normal expectancy, and derived from a common or from a propagated source

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pandemic

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an epidemic of disease spreading throughout human populations across large regions
-an international epidemic

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infectivity

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propensity for transmission
ex: TB has a low infectivity but smallpox has a high infectivity

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pathogenicity

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propensity for an agent to cause disease or clinical symptoms

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virulence

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propensity for an agent to cause severe disease

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Direct transmission

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disease spread by person-to-person or person to animal contact

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indirect transmission

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airborne--droplets or dust particles carry pathogen
vehicle-borne--contaminated air or water or fomite carries pathogen
vector-borne--pathogen spread by an arthopod

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case fatality rate

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(# of deaths from disease during time period)/(# of new cases of that disease same time period)

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mortality rate

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(# of deaths from disease)/(population at risk of acquiring disease)

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attack rate

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(# who become ill during time period)/(# ill + well during same time period)

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herd immunity

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decreased probability that a group will develop an epidemic because proportion of immune individuals reduces the chance of contact between infected and susceptible persons
- entire population does not have to be immunized to prevent the occurrence of an epidemic

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Active surveillance

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-health department initiated
-extensive outreach to identify missed disease cases
-more accurate and complete, but more expensive and labor intensive

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Passive surveillance

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-reporting of cases by providers, hospitals, laboratories
-no outreach to identify missed cases
-less expensive but less accurate--> tends to be more under-reporting

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Steps of an outbreak investigation

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1. establish case definition
2. confirm case diagnosis
3. establish background rate of disease
4. determine if an outbreak is occurring
5. examine descriptive epidemiology
6. generate hypotheses
7. test hypotheses
8. collect and test environmental samples
9. implement control measures
10. inform the public

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Epidemic Curve

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-graphic depiction of cases by time of illness onset
-includes usual or background cases
-issues regarding report delays
-shape tells you:
1. pattern of spread of type of outbreak
2. magnitude or # of cases
3. outliers: index case, secondary case, chance, or not part of outbreak
4. time trend: 1st peak to last peak
5. disease incubation period

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common source outbreak (epicurve)

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-susceptible individuals exposed continuously or intermittently to a common harmful source
-gradual rise in cases with possible plateau
-exposure period may be brief or long

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Common source outbreak with intermittent exposure (epicurve)

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-clusters of cases
-irregular peaks reflect timing and extent of exposures

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Point source outbreak (epicurve)

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-type of common source outbreak where exposure period is relatively brief
-all cases occur within one incubation period
-steep upward slop then gradual downward slope

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propagative outbreak (epicurve)

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-transmission occurs person to person
-may last longer than common source epidemics
-multiple waves of infection can occur
-series of progressively taller peaks, each an incubation period apart

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mixed outbreak (epicurve)

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-initially from a single common exposure but followed by propagative spread
-common with foodborne pathogens

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cases v. controls

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cases: individuals who have disease of interest based on case definition
controls: individuals without disease of interest

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vaccines

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-biological preparation that improves immunity to a particular disease
-contains an agent that resembles disease-causing microorganism
-weakened or killed form of microbe, its toxins, or surface protein
-stimulates body's immune system-->destroy and remember

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types of vaccines

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-prophylactic: prevent effects of future infection by any wild pathogen
-therapeutic: cancer ? ms ?

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vaccine effectiveness

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-impact an immunization campaign will have on the epidemiology of the disease (medium and long-term)
-take something out of the clinic and into the wild
-ongoing surveillance
-maintain high immunization rates

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vaccine efficacy

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-does the vaccine work in a clinical, laboratory setting
-(attack rate of unvaccinated - attack rate of vaccinated)/(attack rate of unvaccinated) x 100