Chapter 2 (Frisch) Flashcards
causality
whether research findings represent cause-and-effect associations
air pollution
associated with increasing urbanisation of developing regions
- exposure to tobacco smoke
toxic chemicals - pesticides, asbestos, lead, and mercury
implicated in cancer, adverse reproductive outcomes, nervous system impacts, and more
epidemiology definition
concerned with the study of the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations
environmental epidemiology definition
refers to the study of diseases and health conditions (occurring in the population) that are linked to environmental factors
why is epidemiology important to the study of environmental health problems?
- many exposures and health effects associated with the environment occur at the population level
- the epidemiologic methods of natural experiments and observational techniques are appropriate
- the study designs used in epidemiological research can be applied directly to the study of environmental health issues
- epidemiology aids in the development of hypotheses and the study of causal relationships
what kind of study design does epidemiology usually take on?
observational study design
descriptive epidemiology
refers to the depiction of the occurrence of disease in populations according to classification by person, place, and time variables
- provide information from setting priorities, identifying hazards, and formulating hypotheses for new occupational risk
analytic epidemiology
examines causal (etiologic) hypotheses regarding the association between exposures and health conditions
- planned examinations of causality and the natural history of disease
- employs both outcome and exposure variables
- takes advantage of naturally occurring situations or events in order to test causal hypotheses (natural experiments)
- example of this is John Snow
prevalence
refers to the number of existing cases of or deaths from a disease or health condition in a population at some designated time
point prevalence
refers to all cases of or deaths from a disease or health condition that exist at a particular point in time relative to a specific population from which the cases are derived
incidence
refers to the occurrence of new disease or mortality within a defined period of observation (e.g., a week, month, year, etc) in a specified population
incidence rate
the rate at which new events occur in population
IR = number of new cases over a time period / average population at risk during the same time period x multiple (e.g. 100,000)
incidence measures
- central to the study of causal mechanisms with regard to how exposures affect health outcomes
- describe the risks associated with certain exposures; they can be used to estimate in a population “the probability of someone in that population developing the disease during a specified period, conditional on not dying first from another disease”
case fatality rate (CFR)
provides a measure of the lethality of a disease, is defined as the number of deaths due to a specific disease within a specified time period divided by the number of cases of that disease during the same time period multiplied by 100
CFR (%) = number of deaths due to disease “X” / number of cases of disease “X” x 100 during a time period
Hippocrates
expounded on the role of environmental factors such as water quality and the air in causing diseases
- produced a well known book on airs, waters, and places
Sir Percival Pott
London surgeon - he is thought to be the first individual to describe an environmental cause of cancer
- chimney sweeps
John Snow
linked a cholera outbreak in London to contaminated water from the Thames River
- natural experiment
Intervention study
is an investigation involving intentional change in some aspect of the status of the subjects
- RCT
- quasi-experiments
quasi-experimental study
manipulation of exposure variable occurs, but individual subjects are not randomly allocated to the study conditions
- community trial
case series study
information about patients who share a disease in common is gathered over time
- weakest for making causal assertions
- useful for developing hypotheses for further study
cross-sectional study
examines the relationship between diseases and other variables of interest as they exist in a defined population at one particular time
- type of prevalence study
- make a one time assessment of the prevalence of disease in a sample that in most situations has been sampled randomly from the parent population of interest
- may be used to formulate hypotheses that can be followed up in analytic studies
ecologic study
a study in which the units of analysis are populations or groups of people rather than individuals
- used to correlate air pollution with adverse health effects such as mortality, researcher measures the association between average exposure to air pollution within a census tract and the average mortality in that census tract
- big problem is uncontrollable factors
case control study
subjects who participate in the study are defined on the basis of the presence or absence of an outcome of interest
- case and controls are generally matched by sex, age, race, etc
- exposure to factor is retro so it already occurred
- examine many potential exposures (advantage)
- examine only one or a few outcomes (disadvantage)
odds ratio (OR)
the ratio of the odds in favour of exposure among the cases (A/C) to the odds in favour of exposure among non cases (the controls, B/D)
A/C / B/D or AD / BC
- an odds ratio of more than 1 suggests a positive association between the exposure and disease or other outcomes
cohort study
classifies subjects according to their exposure to a factor of interest and then observes them over time to document the occurrence of new cases (incidence) of disease
- longitudinal design (follow subjects over time)
- evaluate many different outcomes (causes of death) but few exposures
- either prospective or retrospective
Relative Risk (RR)
RR = incidence rate of a disease in an exposed group / incidence rate of the disease in a unexposed group
- if RR is less than 1, the risk is lower among the exposed group
- this level of risk (less than 1) sometimes is called a protective effect
epidemiologic triangle
Host, agent, and environment (all in a triangle)
- provides a framework for the causation of a disease
consistent association
is one that has been observed repeatedly
specific association
is one that is constrained to a particular disease-exposure relationship
- a given disease results from a given exposure and not from other types of exposures
temporality
observe the cause before the effect
biological gradient
known as a dose-response curve which shows a linear trend in the association between exposure and disease
plausibility
an association must be biologically plausible from the standpoint of contemporary biological knowledge
coherence
suggests that the cause-and-effect interpretation of our data should not seriously conflict with the generally known facts of the natural history and biology of the disease
bias
systematic deviation of results or inferences from truth, or processes leading to such deviation
recall bias
refers to the fact that cases may remember an exposure more clearly than controls (in case-control studies)
selection bias
bias in the effect of an exposure/disease that arises from the procedures used to select participants
example of selection bias
Healthy worker effect
- observation that employed populations tend to have a lower mortality experience than the general population
- which may reduce the validity of exposure data when employed persons are chosen as research subjects in studies or occupational health
confounding
Other outside variables of the study could have influenced the results
- associated with disease risk and produce a different distribution of outcomes in the exposure groups than in the comparison groups
3 major requirements for the successful epidemiologic investigation of environmental exposures are?
- direct and accurate estimates of the exposures experienced by individual members of the study population
- direct and accurate determination of the disease status of individual members of the study population
- appropriate statistical summarisation and analysis of the individual data pertaining to disease and exposure
latency period
refers to the time interval between initial exposure to a disease-causing agent and the appearance of a disease or its manifestations in the host
characteristics, weaknesses, and strengths of environmental epidemiology
Characteristics:
- deals with non-disease effects
- involves numerous variables
- tends to be community specific
Weaknesses
- sample size is insufficient
- important variables “uncontrolled”
- exposure estimation is invalid
Strengths
- engages the real world
- unique perspective on disease/health
- basis for action despite ignorance of mechanism
