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59 Cards in this Set
- Front
- Back
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What is epidemiology? What is the use of epidemiology?
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Investigation of CAUSES and NATURAL HISTORY and prognosis of all types of disease and health outcomes.
To MEASURE and INTERPRET associations between risk factors and disease. |
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What is descriptive epidemiology?
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MEASUREMENT of distribution of a disease
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What is analytic epidemiology?
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MEASUREMENT of association between disease and its risk factors
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What is INTERPRETATION of an association between a risk factor and disease?
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Argument for or against the risk factor effecting the disease.
Ruling out other causes of the association such as BIAS, CONFOUNDING, and CHANCE |
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What are the three components of the epidemiologic model?
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Host
Agent Environment |
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List some common applications of epidemiology...
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- Understand how Dz arises
- Disease management - Test intervention or therapeutic measures - Develop preventative programs and modes of healthcare delivery - Foundation of public policy |
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How do we measure disease burden?
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Morbidity
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What is distribution measurement? What is frequency measurement? What is determinants measurements?
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- Who is getting Dz in a population. Can measure in time, place, or person.
- Quantification of occurrence or existence of a Dz. Can measure over period of time, point in time, or rate over time - Encompasses the two above |
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What is morbidity? What is mortality?
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- illness or disease rate (prevalence)
- death rates (incidence) |
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How should you always express your answer in an epidemiologic problem?
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As per a number. For example: 10.5 deaths PER 100,000
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What is prevalence?
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Number of individuals in a population that have existing disease at a fixed time.
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What is point prevalence?
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Proportion of individuals with disease at a specific point in time.
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What is period prevalence?
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Proportion of individuals with disease over a period of time.
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What is the equation for point and period prevalence?
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Number of existing cases
------------------------------------- Total population |
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Why bother to measure prevalence?
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Prevalence is a measure morbidity and therefore gives you the disease burden in a population.
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What is incidence?
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Number of NEW CASES of a disease arising in an AT RISK population over a specific period of time.
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What is cumulative incidence?
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Proportion of people who become diseased over a specific period of time.
***Inherent assumption: The SAME population is followed for the ENTIRE time interval |
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What is incidence rate/density?
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Some people are not followed for the same period of time so you have to express the time interval in different units. In this case, person-years.
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How do you calculated person-years?
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Duration of following x Number of subjects = Person-Years
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What is the equation for cumulative incidence?
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Number of new cases
------------------------------- Population at Risk |
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What is the equation for incidence rate/density?
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Number of new cases
------------------------------- Person - Years |
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In incidence, you only use the at-risk population. How might this change the population you select for your study?
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You may have to remove some individuals from your population because they may not be at risk. For example, if a person already has disease they are not at risk as they already have it. So, you remove them from your sample.
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If incidence increases, what does prevalence do?
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Increases
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If deaths/cures occur in your population sample, what happens to prevalence?
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Decreases
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What is the second equation for prevalence?
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Prevalence = Incidence x Duration
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What is mortality?
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A type of incidence in which death is the numerator.
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What is the equation for mortality?
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Number of Deaths from Dz
-------------------------------------- Total Population at risk from dying ***At risk could be D+ or D- |
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What are some sub-types of mortality?
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You can calculate the mortality rate by age, disease, or even by more than one characteristic at once. Ex: Number of death in children under 10 from leukemia
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What is case-fatality rate?
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Number of people dying during a specific period of time after onset of a disease
------------------------------------------------------ Number of individuals with the disease ***What percentage of people diagnosed as having a certain disease die within a certain time after diagnosis? |
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What is the difference between case-fatality and mortality?
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Case-fatality only includes those who already have the disease.
Mortality include the total population at risk of dying from the disease -- those who are D+ or D- could all potentially die from the disease |
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How can case-fatality be used?
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- To measure severity of disease
- To measure benefit of new therapy |
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Begin Lecture 2
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Begin Lecture 2
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What are the three kinds of study designs in epidemiology?
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Experimental
Observational/Analytical Descriptive |
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What is an experimental study?
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Prospective/Retrospective study where the experimenter assigns the intervention of interest.
Ex: Clinical Trial using a new drug |
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What is the most common type of experimental study (intervention study?)?
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Clinical Trial
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What is an observational/analytic study?
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A study designed to illicit the cause (etiology) of a disease
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What is the end goal of an observational/analytic study?
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Prevention of the disease, either...
...Primary - remove causative agent or ...Secondary - screening "at risk" people |
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What is the important analytic study we need to know about?
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Cohort Study
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What is a cohort study?
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A study which is designed to investigate the INCIDENCE OF DISEASE in EXPOSED VS NON-EXPOSED populations. In other words, you are determining what exposure may pontentially be causing the disease.
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What is the difference between an intervention study and cohort study? What is similar?
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- An intervention study allows the researcher to choose the exposure whereas a cohort study does not
- They are similar in that they both compare expose vs. non-exposed groups |
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What are some characteristics of a cohort study?
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- Populations defined on those people exposed and not exposed
- At the time of exposure definition, people must be free of disease - Populations followed over time to determine if disease occurs in either group |
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What is a prospective cohort study?
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ASSEMBLE THE COHORT NOW! Follow subjects into the FUTURE!
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What is a retrospective cohort study?
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COHORT ASSEMBLED IN THE PAST! Follow subjects from past to PRESENT!
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What are the two approaches to selecting a cohort study population?
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1. Exposed and Non-exposed are DIFFERENT populations
2. Exposed and Non-exposed are within the SAME population |
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What are the strengths of a cohort study?
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- *Efficient way to study rare exposures
- Maintains temporal sequence - Can examine multiple outcomes of a single exposure - Direct measurement of incidence rates - Measurement of disease rates in exposed vs. non-exposed - Allows measurement of exposures that could never be recalled with accuracy - Can study progression, staging, and natural history of disease - *Recall and Selection Bias minimized |
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What are the weaknesses of a cohort study?
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- *Inefficient for evaluation of rare Dz
- *If prospective, expensive and time-consuming - Long-term commitment - Definitions of exposures and outcomes change - Change in tech effects measurement - If retrospective, need adequate records - Losses to follow-up common |
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A general rule in cohort study is...
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...that we expect more disease in exposed vs. non-exposed populations
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What are the two ways to express the results of a cohort study?
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1. Based on Differences
Attributable Risk, Risk Difference, AR%, Population Attributable Risk, PAR% 2. Based on Ratios Relative Risk |
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What is the risk in the non-exposed called?
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Background risk
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What is the importance of background risk?
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You need to subtract it out of the exposed group's risk to get the risk for just the exposed group
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What is attributable risk?
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Incidence of exposed - Incidence in unexposed = AR
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What is attributable risk percent (AR%)?
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Incidence exposed - Incidence unexposed x100
-------------------------------------------- Incidence exposed The percent of all DISEASED cases that can be attributed to the exposure AKA - "The etiologic fraction" |
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What is PAR?
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Measures the proportion of disease incidence in both exposed and non-exposed that can be attributed to the exposure
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What is the equation for PAR?
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Incidence disease in total population - Incidence disease in unexposed = PAR
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What is PAR%?
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The percentage of the population who have the disease because of the exposure.
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What is the equation for PAR%?
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Incidence disease in total population - incidence disease in unexposed
----------------------------------------------x100 incidence in total population All times 100! |
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What is relative risk (RR)?
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A measure of association between exposure and disease.
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What is the equation for RR?
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Cumulative incidence exposed
-------------------------------------------- x100 Cumulative incidence non-exposed |
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What does a RR above 1 mean? Below 1? Right at 1?
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Above 1 = increased risk
At 1 = no association Below 1 = decreased risk |
