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Epi Final
| Term | Definition |
|---|---|
| epidemiology (definition) | study of distribution and determinants of health-related states or events in specified populations, application of this study to the control of health problems |
| epidemiology (word broken up) | epi: upon demi: people ology: study |
| objectives of epidemiology | - identify etiology/cause of disease - determine extent of disease - study natural history (disease over time) - evaluate new modes of health care delivery and new preventative/therapeutic measures - provide foundation for developing public policy |
| T or F: epidemiology mainly studies population groups, not individuals. | T |
| population (definition) | group of people with a common characteristic such as place of residence, gender, age, or use of certain medical services |
| two types of epidemiology | 1) descriptive 2) analytical |
| descriptive epidemiology (definition) | WHO, WHERE, WHEN - quantifying how often a disease arises in population - frequency of disease may vary from one population group to another |
| measures of disease frequency | 1) prevalence 2) incidence |
| major use of epidemiological evidence | to identify subgroups in the population who are at high risk for disease, really focuses on the most vulnerable |
| EpiCurve | shows progression of illnesses in an outbreak over time |
| What does an EpiCurve help us to see? | when an outbreak starts or when a large amount in the population become infected |
| epidemiological transition | describes changing patterns of population distributions in relation to changing patterns of mortality, fertility, life expectancy, and leading causes of death (ex: from 1900s to now) |
| Does epidemiology often begin with analytical or descriptive data? | descriptive epidemiology - provides rationale for future studies and evaluation |
| What type of epidemiology do determinants come into play? | analytical |
| determinant (definition) | - any physical, biological, social, cultural, or behavioral factor that affects the study outcome - factors or events that are capable of bringing about a change in health |
| risk factors (definition) | causes or exposures that influence health events |
| What questions do risk factors help to answer? | why and how |
| What factors are included in the questions why/how? | - risk factors - causes - modes of transmission |
| Why do we identify subgroups in the population who are at high risk for disease? | - direct preventative efforts, such as screening programs for early disease detection/intervention - to identify modifiable risk factors |
| Examples of modifiable risk factors | - biological agents (bacteria) - chemical agents (carcinogens) - lifestyle (stress, smoking, drinking, sedentary lifestyle, or high-fat diet) |
| Examples of non-modifiable risk factors | - age - gender - family history - ethnicity - disabilities/genetics |
| What does epidemiology investigate? | many different types of health outcomes - infectious diseases - chronic diseases - disability, injury, limitation of activity - mortality - active life expectancy - mental illness, suicide, drug addiction |
| How is disease control accomplished? | through epidemiological research and surveillance |
| surveillance (definition) | watching the disease over time - continuous, systematic collection, analysis, and interpretation of health related data needed for planning, implementation, and evaluation of public health practices - can be long term/acute surveillance |
| How is surveillance carried out? | - by federal (CDC) - state (state health departments) - local agencies (local health departments) |
| measures of frequency (definition) | rate with which an event occurs in a defined population over a specified period of time |
| measures of frequency (examples) | - counts - prevalence - incidence rates (typically expressed in ratios, n/d) |
| measures of association (definition) | relationship between exposure and disease among the two groups |
| measures of association (examples) | - relative risk - odds ratio - prevalence ratio |
| statistical inference (definition) | interpreting study results - determining if #/ratios we find can be applied to larger populations/groups |
| statistical inference (examples) | - p value - confidence limits |
| primary prevention (definition) | preventing the initial development of disease - limits exposure of disease in the first place |
| primary prevention (examples) | - reducing exposure through a risk factor through IMMUNIZATIONS - legislation/enforcement banning/controlling use of hazardous products - mandate/education of safe and healthy practices |
| secondary prevention (definition) | early detection of existing disease to reduce severity/complications - prevents further complications/mortality |
| secondary prevention (examples) | - screening for cancer - exercise/diet to prevent further health problems - use of aspirin |
| tertiary prevention (definition) | reducing impact of disease for an individual who has already reached a point of disability, impairment, or dependency - avoids present complications from getting worse |
| tertiary prevention (examples) | - rehab - support groups - antibiotics/insulin |
| John Snow | - father of epidemiology - investigated cholera outbreak in Broad Street, Golden Square, London |
| Edward Jenner | developed Smallpox vaccine |
| Ignaz Semmelweis | - studied childbed fever - championed hand washing |
| components of Epi Triad | host, agent, environment, vector |
| host (epi triad) | Who becomes infected with the disease? |
| agent (epi triad) | What pathogen/what is causing the disease? |
| environment (epi triad) | Where the disease is taking place? |
| vector (epi triad) | movement of the disease ex: mosquito, tick for lyme disease |
| Goal of Epi Triad | to break at least one of the sides of the triangle, disrupting connection between the environment, host, agent, and stopping the continuation of the disease |
| characteristics of a host | once an agent infects a host, degree/severity of the infection will depend on the host's ability to fight off infectious agent |
| Two types of defense mechanisms present in host | - nonspecific: diff defense mechanisms that body produces ex: skin, mucosal surfaces, tears, saliva, gastric juices - disease-specific: certain pathogen/disease |
| Three types of agents of infectious diseases | - biological - physical - chemical |
| Examples of biological agents | - bacteria - viruses - mycoses (fungal diseases) - protozoa |
| Examples of physical agents | - noise - repetitive motion - violence |
| Examples of chemical agents | - tobacco - air pollutants - water pollutants - cleaning chemicals |
| Modes of transmission (definition) | any mechanism by which an agent is spread to the host |
| Types of modes of transmission | - Direct (person to person) - Indirect (airborne, droplet, fecal/oral, bodily fluids) - Vector - Vehcile |
| Vector (definition) | - most often an insect or arthropod, conveys the infectious agent from reservoir to a susceptible host (ex: mosquito, flea, tick) |
| Vehicle (definition) | - non-living intermediary, such as food, water, biological product, or inanimate object (handkerchief, bedding, surgical scalpel) that conveys infectious agent from its reservoir to a susceptible host |
| infectivity (definition) | likely to infect - capacity of an agent to produce infection/disease - measured by secondary attack rate |
| pathogenicity (definition) | likely to cause illness - capacity of the agent to cause disease in the infected host |
| virulence (definition) | severity of the illness - measured by the proportion of severe/fatal cases |
| toxigenicity (definition) | capacity of an agent to produce a toxin/poison |
| incubation period (definition) | time interval from infection to onset of symptoms - time needed for the organism to replicate to induce infection |
| quarantine (definition) | separates and restricts movement of people who were exposed to a contagious disease to see if they become sick |
| isolation (definition) | separates sick people with a contagious disease from people who are not sick |
| latency period (definition) | incubation period for noninfectious disease - ex: mesothelioma resulting from Asbestos exposure may be 20-30 years |
| Herd Immunity (definition) | aka community immunity - individuals who are not immune to a pathogen from exposure by the large amounts of immune individuals within the community |
| Herd Immunity Threshold (definition) | proportion of the population that must be immune in order to prevent disease from spreading from person to person ex: target is 95% for MMR |
| certain conditions for herd immunity | - single host species - solid immunity (large percent of the population is immune) - no variation in population immunity (ex: only vaccinating adults and not children) |
| epidemic (definition) | increase in the number of cases of a disease above what is normally expected in that population area |
| outbreak (definition) | carries the same definition as epidemic, but is often used for a more limited geographic area |
| endemic (definition) | constant presence of disease or infectious agent in a population within a given geographic area |
| pandemic (definition) | worldwide epidemic |
| 3 types of outbreaks | - common-source point - common-source continuous - propagated/progressive souce |
| Common point source (definition) | - group of people are all exposed to an infectious agent or a toxin from the same source - same pathogen (common source) - sudden and rapid increase in # of cases of disease |
| What type of outbreak is most common for foodborne outbreaks? | Common point source |
| Common continuous source (definition) | - common underlying cause, exposure to an infectious agent/toxin from same source - exposure to the source is prolonged over an extended period of time - people become exposed at all different times and areas |
| What type of outbreak is most common for waterborne illnesses? | Common continuous Source Outbreak |
| Propagated source (definition) | - type of outbreak is caused by a transmission from one person to another which requires direct contact - can last longer than common source outbreaks - may have multiple waves - difficult to identify incubation period |
| What type of outbreak is COVID-19? | Propagated source |
| cluster (definition) | - unusual aggregation of cases grouped in time and place that are suspected to be greater than the number expected, even though the expected number may not be known - without regard to whether number of cases is more than expected - no evid of epi link |
| epidemiological link (definition) | learning how cases are connected |
| outbreak (definition) | increase in number of cases of a disease above what is normally expected in that population in that area - cases have confirmed contact/common source of infection (clear epi link) |
| Steps of an Outbreak Investigation (1-6) | 1) Confirm existence of an outbreak 2) Define a case (case def) 3) Define the num (cases), how many cases? 4) Define the demon, what is the pop at risk? 5) Examine cases by place, time, and person 6) Calculate attack rates/ratio |
| Steps of an Outbreak Investigation (7-9) | 7) Evaluate Hypothesis & test/perform additional studies 8) Recommend control measures to control/prevent future similar outbreaks 9) Communicate findings to those involved in public development and to the public |
| What does a case definition include? | standard set of criteria of deciding whether an individual should be classified as having the health condition/disease of interest - person, place, time, burden |
| line listing (definition) | info is collected using a questionnaire/case report form then described on a form known as line listing |
| How do you find the population at risk of developing a disease? | those with disease/those with a chance they could get it example: ovarian cancer - those with it/those with ovaries |
| How do you find the prevalence? | # of people affected present in a pop at a specific time/# of people in pop at that specific time |
| How do you find the incidence rate? | # of new cases of a disease in a specific period of time in a population at risk for developing the disease |
| How do you find the attack rate? | new cases/total population at risk (as a percent) |
| How do you find the food-specific attack rate? | number of people who ate that food and became ill/total number of persons who ate that food |
| passive surveillance | - rely on health care providers /laboratories to report cases of disease - often incomplete |
| active surveillance | - health department is proactive - more costly/labor intensive - provides a more complete picture |
| T or F: Rate is a measure of risk. | T |
| public health surveillance (definition) | ongoing, systematic collection, analysis, and interpretation data |
| total person-time (definition) | total time that all participants contributed to a study - person contributes to person-time while they disease free - once person develops a disease/is no longer a part of the study, the amount of time they contribute ends |
| calculation of person-time | person-years of observation - all the people in the population being studied are observed for the entire period |
| T or F: If duration of disease is short and incidence is high, prevalence becomes more similar to incidence. | T |
| What factors increase prevalence? | - longer duration of disease - prolongation of life of patients w/o cure - increase in new cases - in-migration of cases/susceptible people - out-migration of healthy people - improved diagnostic facilities (better reporting) |
| What factors decrease prevalence? | - shorter duration of disease - high case-fatality rate from disease - decrease in new cases - inmigration of healthy people - outmigration of cases - improved cure rate of disease |
| Why do we use midyear population for Annual Mortality rate? | pop changes over time, # of persons in the pop at midyear is used as an approximation of average pop |
| What is fertility rate used for? | used for comparisons of fertility among age, racial, and socioeconomic groups |
| category specific rates | specific rates refer to a particular subgroup of the pop defined in terms of race, age, sex, or single cause of death/illness |
| How are category specific rates helpful? | - in identifying subgroups at risk for developing a disease - plan intervention |
| screening (definition) | - identification of unrecognized disease/defects by application of tests, exams, or other procedures that can be applied rapidly - for indivs who haven't exhibited any symptoms, in order to classify them w/ respect to probability of having the disease |
| validity of a screening test | ability of a test to distinguish between those who have a disease and those who don't |
| What are the two components of validity? | - specificity - sensitivity |
| Specificity (definition) | ability of the test to identify correctly those who do not have the disease - proportion of non-diseased people who were correctly identified as negative |
| Sensitivity (definition) | - ability of a test to identify correctly those who truly have the disease - proportion of disease people who were correctly identified as "positive" by the test |
| true positive | have the disease and test positive |
| false positive | does not have the disease but test positive |
| true negative | does not have the disease and tests negative |
| false negative | have the disease but test negative |
| bimodal curve | distribution in which there are two peaks |
| What is the likelihood that this patient actually has the disease? | positive predictive value |
| What is the likelihood that this patient actually doesn't have the disease? | negative predictive value |
| The _______ the prevalence of the disease, the _______ the positive predictive value. | higher, higher |
| Characteristics of a good screening test | - simple - rapid - inexpensive - safe - acceptable |
| observation studies | study participants are observed, no action from researcher - investigators observe the natural history of the disease in subjects w/o assigning treatments to the subjects |
| experimental studies | intervention of the researcher, observe what happens to study participants as a result of intervention - investigators apply treatment to subjects |
| case report (defintion) | detailed report on one patient, usually new or unusual problem/symptom |
| case series (definition) | detailed report on a group of patients with the same symptom or problem, usually new or unusual |
| benefits of case report/series | - recognition and description of new diseases, new manifestations of old diseases - detection of drug side effects - provide insight into disease mechanisms - provide information help develop hypotheses |
| limitation of case report/series | no explicit comparison group |
| ecological studies (definition) | study that examines rates of disease in relation to a population-level factor - unit of observation=group - exposure and outcome data at group level |
| ecological fallacy/bias | exposure is measured as an average for a population, not a person, so there is no real link between exposure and disease - group-level association may not transfer to the individual level |
| ecological studies (strengths) | - inexpensive and fast, conducted on available data - good for early knowledge - wider range of knowledge than other types of studies |
| cross-sectional studies (definitions) | study/survey that examines the relationship between an exposure/disease at a single point in time - single point of observation - takes a snapshot - measures exposure prevalence in relation to disease prevalence |
| Many government studies are _________ | cross-sectional |
| limitations of cross-sectional studies | problematic when exposure is interchangeable (smoking, drinking, physical activity) |
| What are cross-sectional studies OK for? | - immutable characteristics (genetic traits, blood type) - measure of long term exposure (lead in bones) - historical exposure (activity level over 30 years) |
| Strengths of cross-sectional studies | - relatively quick and inexpensive - highly generalizable - hypothesis generation - health care planning - estimation of magnitude/distribution of a health problem |
| Purpose of case control studies | identify and count cases of disease - monitors public's health - generate hypotheses about causes of disease |
| observational studies | - investigators observe the natural history of the disease in subjects without assigning treatments to the subjects |
| experimental studies | - investigators apply treatments to individuals - investigates role of some factor/agent in the prevention/treatment of a disease |
| types of observational studies | - cohort - case control - cross sectional |
| types of experimental studies | - randomized clinical trials - community trials |
| Process of case-control studies | 1) define hypothesis 2) define source pop 3) identify cases from the source pop 4) identify valid comparison group (controls) from the same source pop 5) ascertain exposure for cases&controls 6) calculate measure of association b/w cases&control |
| two groups in case-control studies | case: group of people with the disease control: group of people without the disease |
| Control group is also called.... | comparison group |
| source population (definition) | population you are interested in knowing more about - pop that gave rise to cases - consider hypothesis, person, place, time when defining a source pop |
| How do investigators cases/controls? | identifies CASES of disease and selects CONTROLS who represent a sample of the source pop that produced the cases |
| purpose of controls | estimate the exposure distribution in source population that produced the cases |
| control selection | - controls must come from the same source population as the cases -controls must be selected independently of exposure |
| Where to find controls? | - population based controls - hospital or clinic based controls - friends/relatives identified by cases - nested controls from cohort population/study |
| population-based controls | controls selected from the general population, most suitable when cases are from well-defined geographic area |
| control selection requirements | - must come from the same source population as the cases - controls must be selected independently of exposure |
| strengths of case-control studies | - tend to use smaller sample sizes than surveys or prospective studies - quick and easy - cost effective - useful for studies of rare diseases |
| limitations of case-control studies | - does not provide direct estimate of risk - timing of exposure-disease relationship difficult to determine - not efficient to study rare exposure - prone to recall bias |
| measures of disease frequency (definition) | characterizes the occurrence of disease, disability, or death in human population (examples: measure of morbidity and mortality) |
| measures of association (definition) | assess the strength of the statistical relationships between a given study factor and a disease examples: prevalence ratio, odds ratio, relative risk |
| What type of study uses prevalence ratio? | cross sectional |
| What type of study uses odds ratio? | case control |
| What type of study uses relative risk? | cohort and experimental |
| interpretation of a prevalence ratio | pr=1 no association pr>1, prev in exposed is greater than prev in non exposed RISK FACTOR pr<1, prev in exposed less than prev in non exposed PROTECTIVE FACTOR |
| interpretation of an odds ratio | OR=1 no association OR>1, risk factor OR<1, protective factor |
| prospective cohort studies | - identifies the original pop at the beginning of the study and subjects who are exposed and unexposed - follows subjects real-time until the point at which the study ends OR to assess if the disease develops or not |
| retrospective cohort studies | - identifies the original population using historical data and exposed/nonexposed people in the case, regardless of outcome status - traces individuals forward in time the present day and will then assess if disease develops or not |
| Prospective is _______ in time, retrospective is ______ in time | forward, backward |
| design of a randomized trial | 1) begin with a defined population 2) participants are randomized to receive with a new treatment/current treatment 3) subjects are followed in both groups to determine who improved and who did not improve |
| Two characteristics of experimental studies | 1) manipulation of the study factor 2) randomization |
| single blind design | subject unaware of group assignment |
| double blind design | neither subject nor experimenter is aware of group assignment |
| intent to treat analysis | gives information on the effectiveness of a treatment under everyday practice conditions |
| ethical issues of human experimentation | - informed consent - monitoring for side effects - deciding when to withdraw a patient - protecting the interests of patients |
| measures of effect | measure's expected contribution of a study factor to the frequency of a disease in a particular population - useful in predicting the efficacy/effectiveness and facilitates in planning/evaluation of intervention |
| attributable risk | only can be computed directly from a cohort study - portion of the incidence of a disease in the exposed that is due to the exposure |
| How much of the disease that occurs can be attributable to a certain exposure? | attributable risk |
| population attributable risk | determining which exposures have the most relevance to the health of a pop/community - interested in total pop and not just in exposed groups - total pop consists of exposed and non-exposed groups |
| random error (definition) | occurs because the estimates we produce are based on samples, and samples may not accurately reflect what is really going on in the pop at large |
| bias (definition) | systematic error is the design, conduct, or analysis of a study that leads to an erroneous association between the exposure and disease (low validity) |
| reliable=_____ | precise |
| accurate=_______ | valid |
| bias towards the null means... | weakening association |
| bias away from the null means... | strengthening association |
| goal achieve internal validity | the extent to which the association results represent the truth in the pop we are studying |
| random error | - affects precision; how close values are to each other - error in either direction - can be helped with larger sample size |
| systematic error | - affects accuracy (how close values are to true value) - same error in same direction in all measurements - cannot be minimized with larger sample size |
| sources of systematic error | selection bias: selection of study participants information bias: classification and measurement confounding bias: comparison and interpretation |
| non-response bias | low or moderate participation rates can result in selection bias due to non-response or refusal to participate if it is related to both exposure and disease |
| What is the best way to avoid non-response bias? | achieve high participation rates among cases and controls |
| selection bias | may occur in cohort studies if the exposed and unexposed groups are not truly comparable |
| healthy worker effect | type of selection bias that may occur when a group of people exposed to an occupational hazard is compared with the sample of the general population |
| differential loss to follow up | bias due to differences in completeness of follow-up between comparison groups examples: study of disease risk in migrants |
| information bias (definition) | error in measuring exposure, covariate, or outcome variables that results in diff quality (accuracy) of information between comparison groups - occurs after the subjects have entered the study |
| misclassification (of information bias) | case-control studies: cases may be misclassified as controls and controls may be misclassified as cases cohort studies: exposed group may be misclassified as non exposed and unexposed group may be misclassified as exposed |
| non-differential misclassification | problem inherent in the data collection methods - occurs when there is an equal likelihood of both groups being misclassified |
| non-differential misclassification (consequence) | weakening of measure of association |
| recall bias | - results from differential (differences in completeness of follow up) recall of past exposure |
| What type of study is recall bias a concern? | context of case control studies, when cases and controls are asked about exposures in the past |
| interviewer bias | - may influence subjects' ability to remember information because of the preconceived notion about the hypothesis being examined |
| methods to avoid information bias | - masking interviewers and subjects to the study hypothesis (interviewer and recall) - using control group that is composed of diseased info (recall) - carefully designing study questionnaire (both) - relying on non interviewer data (both) |
| When can selection bias occur? | beginning of the study/subject enrollment |
| When can information bias occur? | data collection |
| When can confounding bias occur? | data analysis or beginning of the study |
| confounding bias (definition) | distortion (inaccuracy) in the estimated measure of association (OR, RR) - problem of comparison, a problem that arises when extraneous but important factors are differently distributed among groups being compared |
| When does confounding bias occur? | when primary exposure of interest is mixed up with some other factor that is associated with the outcome |
| confounding variable (definition) | outside variable that correlates (positively or negatively) with both the outcome and exposure |
| criteria for potential confounding factor | 1) must be a risk factor for the disease even in the absence of exposure 2) must be independently associated with the exposure 3) must not be in a causal pathway (not be the result of the exposure) |
| Why do confounding variables matter? | ensures the internal validity we must account for confounding variables - results may not reflect the actual relationship/association between the exposure and outcome if outside variables are not considered |
| types of confounding | 1) a priori confounding (based on prior knowledge) 2) data based confounding (based on data) |
| cause (definition) | an event, condition, or characteristic that plays an essential role in producing an occurence of the disease |
| sufficient cause | factor (or more usually a combo of several factors) that will inevitably produce disease |
| necessary cause | any agent that is required for the development of a given disease |
Created by:
etarno
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