Environmental Health Ch 2
confounding
distortion of a measure to the effect of an exposure on an outcome due to the association of the exposure w/ other factors that influence the occurence of the outcome ex. thinking construction workers get lung cancer due to dust but in reality its because they smoke more
selection bias
distortions that result from procedures used to select subjects and form factors that influence participation in the study ex. healthy worker effect
epidemiologic triangle: environment
domain in which disease causing agents may exist, survive, or originate
hill's criteria of causality : biological gradient
dose-response curve
strengths of environmental epidemiology
engages the real world unique persepctive on disease/health basis for action despite ignorance of mechanism
why are researched often prohibited from using experimental methods? what do they do instead?
ethical issues such as potential dangers to subjects observational science that takes advantage of naturally occurring situations in order to study the occurrence of disease
case fatality rate (CFR)
measure of the lethality of a disease (number of deaths due to disease X / number of cases of disease X ) * 100 during a time period
3 major requirements for the successful epi investigation of environ exposures
1. direct and accurate estimates of the expsoure experienced by indiivdual members 2. direct and accurate determination of the disease status of individuals 3. appropriate statistical summarization and analysis of the individual data pertaining to disease and ezposure
epidemiology is important to the study of envrionmental health problems b/c ____, ___, ____, ____
1. many exposures and health effects associated w/ the eviron occur at the pop level 2. epi methods of natural experiments and observational techniques are appropriate 3. study designs used in epi research can be applied directly to the study of environ health issues 4. epi aids in the development of hypotheses and the study of causal relationships
epidemiologic triangle
3 major factors: host, agent, environment
incidence rate
=(number of new cases/total population at risk over a time period ) x multiplier (like 100,000)
hill's criteria of causality : consistency
a consisntent association is one that has been observed repeatedly by different persons, in different places, circumstances, and times
hill's criteria of causality : specificity
a given disease results from a given exposure and not from other types of exposures one-to-one causation is unusual b/c many diseases have more than one causal factor
disease clustering
a closely grouped series of events or cases of a disease or other health-related phenomena with well defined distribution patterns in relation to time or place or both; term is usually used to describe aggregation of relatively uncommon events or diseases like leukemia may suggest common exposure to environmetal hazard
ecologic study
a study in which the units of analysis are populations or groups of ppl rather than individuals; many uncontrolled factors
point prevalence
a type of prevalence 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 =number of persons ill / total number in the group at a point in time
2 primary functions of descriptive epi
assess variations in the occurrence of disease in populations aid in the development of etiologic hypotheses
hill's criteria of causality : plausibility
association must be bioloigcally plausible from the standpoint of contemporary biological knowledge
why is the incidence rate considered a rate?
b/c of the specification of the time period during which the new cases occur
recall bias
cases may remember an exposure more clearly than controls
polychlorinated biphenyls (PCBs)
classified as dioxin-like chemicals, these substances comprise an extensive class of organochlorines; thru biological processes can become increasingly concentrated in foodstuffs, are potential carcinogens, & can impact reproductive system
cohort studies
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; type of longitudinal design; prospective or retrospective; uses Relative risk
epidemiology aids the envrionmental health field thru ____, ___, ____, ____
concern with populations use of observational data methodology for study designs descriptive and analytic studies
characteristics of environmental epidemiology
deals with nondisease effects involves numerous variables tends to be community specific
time variables
decade, year, month, week, day
examples of person variables
demographic characteristics such as sex, age, and race/ethnicity
place variables
denote geographic locations including a specific country or countries, and places where localized patterns of disease may occur
descriptive epidemiology
depiction of the occurrence of disease in populations according to classification by person, place, and time variables ; fundamental approach by epidemiologists; aim to delineate the patterns and manner in which disease occurs in a pop
hill's criteria of causality
evaluation of causal association based on nine causal criteria: strength consistency specificity temporality biological gradient plausibility coherence
analytic epi
examines causal (etiologic) hypotheses regarding the association b/w exposures and health conditions propose and evaluate causal models that employ both outcome variables and exposure variables
healthy worker effect
example of selection bias employed people chosen as research subjects in studies of occupational health b/c healthier people likely to be employed reduced measure of effect for an exposure that increases morbiidity and mortality
hippocrates
expounded on the role of environmental factors such as water quality and the air in causing diseases didnt delineate specific known agents involved in the causality of health problems
epidemiologic triangle: agent
factor such as a microorganism, chemical substance, or form of radiation, whose presence of relative absence is essential for theoccurrence of disease
sir percival pott
first individual to describe an environmental cause of cancer, suggest a way to prevent the disease, led indirectly to the synthesis of the first known pure carcinogen and the isolate of the first carcinogenic chemical to be obtained from a natural product chimney sweeps had a high incidence of scrotal cancer(he hypothesized b/c of soot) ; occupational hygiene measure- recommended chimney sweeps bathe once a week foundation of cancer prevention
TX sharpshooter effect
in a random distributions of cases of cancer over a geographic are, some cases will appear to occur very close together just on basis of random variation. ex. painting targets around bullet holes after shooting
case series study
info about patients who share a disease in common is gathered over time; weakest for making causal assertions; can be useful for developing hypotheses for further study ; info is preliminary and a starting point
intervention study
intentional chance in some aspect of the status of the subject
long latency period
limit to ability to derive causal inferences
low incidence and prevalence
limit to ability to derive causal inferences dependent on less powerful research designs such as descriptive and case control studies
difficulties in exposure assessment
limit to ability to derive causal inferences levels of expsoure (esp low level) often uncertain sometimes several expsosures are mixed
john snow
linked a cholera outbreak in london to contaminated water from the thames river; natural experiment methodology; 1855: Nuisances Removal and DIsease Prevention Amendments Bill- reform of pbh legislation to control release into the atmosphere of fumes from operations such as gas works, silk boiling works, and bone boiling factories; Snow contended that these odors were not a disease hazard in the community b/c people with high exposures who worked in these factories didn't have ill health effects, so at a lower exposure the community shouldn't either
randomized contrlled trials
manipulation of an exposure variable and random assignment of subjects to either a treatment group or a control group tests the efficacy of new medications, medical regimens, and vaccines
quasi experiments
manipulation of an exposure variable, but subjects are not randomly allocated to the study conditions (ex. treating one city with fluoridated water and the other with plain)
advantage of using mortality as an end point
may be relevant to agents that have a subtle effect over a long period of time
odds ratio (OR)
measure of association b/w exposure and out come used in case control studies; uses 2X2 table; OR=(a/c)/(b/d)=(ad)/(bc) ; >1 suggests positive association
natural experiments
naturally occuring circumstances in which subsets of the pop have different lvls of exposure to a supposed causal factor, in a situation resembling an actual experiment where human subejcts would be randomly allocated to groups ex. john snow's work
nonspecific effects
nonspecific outcome- associated w/ several different environemntal expsoures majority of the diseases thought to be related to environmental expsures are influenced by many factors complicated
epidemiologic triangle: host
person or other living animal that affords subsistence or lodgment to an infectious agent under natural conditions
weaknesses of environmental epidemiology
sample size is insufficient important variables "uncontrolled" exposure estimation invalid
Descriptive studies provide info for__, ___, ___
setting priorities identifying hazards formulating hypotheses for new occupational risk
hill's criteria of causality: strngth
strong associations give support to causal relationship b/w factor and disease but should not be too ready to dismiss causal associations when the strngth of the association is small
unique characteristic of epi
studies the entire population and therefore sometimes called population medicine
environemental epidemiolgy
study of diseases and health conditions that are linked to environmental factors; exposures usually may be considered involuntary (exposure factors lie outside the individual's immediate control) ; focus on health effects linked to degredation of the air we breath, the water we drink, and the food we eat
epidemiology
study of the distribution and determinants of health and diseases, morbidity, injuries, disability, and mortality in populations
case control studies
subjects who participate in the study are defined on the basis of presence of absence of an outcome of interest; exposure to factor determined retrospectively; uses odds ratio
bias
systematic deviation of results or inferences from the truth
hill's criteria of causality : coherence
the cause and effect interpretation of our data should not seriously conflict with generally known facts of the natural history and biologu of the diseaes
standardized mortality ratio (SMR)
the ratio of the # of deaths observed in the study group to the # that would be expected if the study pop had the same specific rates as the standard population (often multiplied by 100) ; denoted by a percentage ; about 100% means the SMR in the study pop is higher than the comparison pop
relative risk (RR)
the ratio of the incidence rate of a disease in an exposed group to the incidence rate of the disease in a non exposed group; RR = (A/A+B)/(C/C+D); >1 statistically significant /positive association <1 protective largely affected by disease misclassification
latency
the timer interval b/w initial expsure to a disease causing agent and the appearance of a disease or its manifestations in the host
population at risk
those members of the pop who are capable of developing the disease or condition being studied
cross secctional studies
type of prevalence study in which the distribution of disease and exposure are determined; one time assessment of the prevalence of disease; may be used to formulate hypotheses that can be followed up in analytic studies
hill's criteria of causality : temporality
we must observe the cause before the effect
