public health exam one

Epidemiology

study of the distribution and determinants of health-

related states or events in specified populations and the application of this

study to the control of health problems

epidemiologic process

surveillance, risk factor identification, intervention evaluation, implementation

community level data

polltion, weather, policies

causal interference

estimate effect of an exposure, treatment, policy, or intervention on an outcome.

web of causation

Disease often results from complex set of many interconnected factors

• Individual: genetics, behaviors, biological factors

• Social/environmental: family, work, neighborhood, culture, healthcare

access

hills causal criteria

experimental evidence, temporal relationship, strength of association, dose-response, biological plausibility, consistency.

Plus analogy, specificity, and coherence

experimental evidence

there is scientific evidence of an association

Temporal relationship

exposure precedes development of outcome

Strength of the association

stronger associations more likely to be causal

Dose-response:

greater exposure, more outcome

Biological plausibility

there is a reasonable proposed biological mechanism

Consistency:

observe association in different contexts with same results

Analogy

similar exposures can cause similar outcomes

Specificity

a particular exposure is associated with a particular outcome

Coherence

similar results in laboratory and epidemiological studies

causal pie

Causes can be:

• Sufficient: the single cause or set of causes that are necessary and contributing to make disease inevitable

• Component: single condition that is part of at least one sufficient set.

• Necessary: appears in every single sufficient set

sufficient cases

all combinations of causes in a pie are sufficient to produce outcome

component causes

all sufficient cases will be component

necessary causes

cause found in all cases

cons for causal pies

• We usually do not know all component causes

• Complete sufficient causes are difficult to identify empirically

• Primarily a conceptual rather than quantitative model

Susser’s Pragmatic Causal Criteria

1) Association: exposure and outcome occur together more often than expected

2) Time order: the exposure occurs before the outcome

3) Direction: the causal pathway runs from exposure to outcome, not the reverse

Etiologic factor

a factor that contributes causally to the development of the disease.

normal phase

no disease present

preclinical phase

begins after etioliogic exposure to disease

clinical phase

when symptoms first appear, also phase during which disease is diagnosed and treated

secondary prevention

screening or testing asymptomatic individuals

tertiary prevention

To reduce the impact of disease among diseased individuals who have already been diagnosed.

To decrease the likelihood of recurrence in someone who has already been diagnosed.

Subclinical Infectious Period

time interval from start of infectiousness to the onset of symptoms (infectious, but no symptoms yet)

Outbreak:

essentially an epidemic, often in a smaller/localized setting

epidemiologic triad

Host, Agent, and Environment interactions produce disease. Vector is in the middle

attack rate

# people who became ill/

# people at risk (ill + not ill)

attack rate ratio

attack rate in exposed group/

attack rate in unexposed group

Social Incongruity Theory

A mismatch between an individual’s social position and the expectations or norms of their social environment can create stress and disadvantage.

Person-Environment Fit Model:

Health and well-being depend partly on how well a person’s needs, abilities, and characteristics match the demands and resources of their environment

Stress Process Model:

Stress affects health through a process that unfolds over time and its effects depend on the resources people have to cope with it

social determinants of health

health care access and quality, neighborhood and built environment, social and community context, economic stability, education access and quality

Economic Stability

Income vs. cost of living, unemployment rate (employment status), difficulty paying for basics (food, bills, rent etc.), debt

Education Access and Quality

attendance rates, high school graduation rates (kids can’t go to school, transportation, indication of community resource.), school funding local taxes (more affluent areas have more funding), state test scores, class teacher ratio, public vs. private schools

Social & Community Context

Household size, exposure/access to diverse people and experience, opportunities for community participation (churches, youth organization, city commissions, etc.) self report of feelings of social ties..(survey: have neighbors safe? Street is safe? Social cohesion space, accessible places..)

Neighborhood and Built Environment

Street lights, safety, walkability , parks (green space) (we ask these self-reporting survey OR we can decide it through maps geo-coding), playgrounds, distance to grocery stores, history of redlining, proximity to industry (exposure to environmental hazard, so close to major business), person square footage (urban vs. rural) population density (for contagious disease)

Health Care Access and Quality

Proximity to a hospital/healthcare facility, health insurance (types), kinds of healthcare facilities (specialty clinics, stability of providers, urgent care), specialist doctors per population, trust in healthcare providers, (choice) options for treatment, amount of PCP

detectable pre-clinical phase

time between disease being detectable by screening and symptoms appearing

Lead Time

how much earlier screening detects a disease compared with diagnosis after symptoms

Valid/Accurate, not Reliable

repeated measurements are centered around the true value (avg)

individual measurements vary widely. if you repeat the test, you get different answers each time

Reliable, not Accurate

repeated measurements give similar results (tightly clustered together), but are not on target

Sensitivity:

aof a test to correctly identify those who have the disease

(True Positive Rate)

Specificity:

Ability of a test to correctly identify those who do not have the disease

(True Negative Rate)

calculating sensitivity

diseased who screen positive/ all diseased (true pos and false neg)

caluclating specificity

non-diseased who screen negative/all non-diseased (true neg and false pos)

Passive Surveillance

Outcomes are reported by health care providers

Active Surveillance

Health agencies contact health providers seeking reports

Prevalence

EXISTING cases (new + pre-existing)

how widespread a disease is

Incidence

NEW cases

how quickly a disease spreads

Point Prevalence

number of people with an event (outcome, Y=1) at a specific time point divided by the size of the population

Calculating Point Prevalence

# people who ARE cases at a specified time/

Number of persons in the population at that time

Period Prevalence

proportion of a population with an event (outcome, Y=1) [or, exposure, X=1] at any time during the specified period

Cumulative Incidence

# people who became newly ill during time of interest/

# people at risk during the time of interest

Person-Time

# people who became newly ill during time of interest/

Total person-time at risk

Incidence Rate

# people who became newly ill during time of interest/

Person-time at risk

Case Fatality “Rate”

# of deaths from the disease/

# of people who have the disease