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Epi

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jmnies's version from 2016-12-08 02:49

Section

Question Answer
Percentage of students enrolled in a college who developed influenza during the spring semester of 2001Cumulative incidence
Percentage of students enrolled in an epidemiology class who had sore throats on the first day of classPrevalence
Percent of breast cancer patients who underwent mastectomy during 2001Cumulative Incidence
Percent of men found to have high blood pressure at their yearly physicalPrevalence
Number of newly-diagnosed cases of AIDS in a year per 100,000 personsIncidence Rate or Cumulative Incidence
Percent of infants born with spina bifida out of 1,000 liveborn infantsPrevalence
Percent of drivers found to be legally drunk at the time of their car accidentPrevalence
Cumulative incidence and incidence rateThe key difference between cumulative incidence and incidence rate is the way that each handles time. Time is not integrated into the cumulative incidence measure (it is mentioned in words that go along with the number) while time is an integral part of the incidence rate denominator
Cumulative incidencemeasures the proportion of a candidate population that becomes diseased over a specified period or time.
Incidence ratemeasures the rate of occurrence of new cases of disease in a candidate population. Its denominator is comprised of person-time of observation in the candidate population
What is the defining feature of an experimental study?The investigator allocates therapeutic or preventive regimen.
What are the different types of experimental studies?Community vs. individual, preventive vs. therapeutic. parallel vs. crossover, simple vs. factorial
Reference populationthe population to whom the study results are generalizable.
Study or experimental populationthe population who are considered for enrollment in the study, that is, potential participants.
Randomizationa treatment allocation method in which each individual has the same chance of receiving each treatment.
Compliancedegree to which study subjects adhere to assigned treatment protocol
Placeboinert agent indistinguishable from the active treatment
Maskingthe study participants and/or the investigator do not know which treatment group each study participant is in. In single masked studies, only the participants are unaware of the treatment assignment while in double-masked studies, both the investigators and participants are unaware.
What are the main issues to consider in choosing a study population for an experimental study?Suitable disease, generalizability, accessibility, compliance, follow-up, sufficient endpoints, sample size
What are the main purposes of randomization?To achieve baseline comparability of known and unknown confounders between the treatment and comparison groups. To eliminate bias in assignment to treatment group
What is the purpose of using a placebo?Placebo makes the treatment and comparison groups comparable with respect to their study” experience.” It also allows masking to be achieved.
What is the purpose of masking?To eliminate bias in follow-up and outcome ascertainment
Name some methods by which good compliance may be achieved.Use a motivated group, design a simple protocol, have frequent contact with participants, give them incentives, use calendar packs to help with pill taking, have a run-in period
What problem results when compliance is poor?The compared groups become more similar and so the ability to detect true differences between the groups is reduced
What is the purpose of ascertaining follow-up uniformly in both the treatment and comparison groups?eliminate bias
Give the definition of a cohort studyA study in which investigators follow two or more groups of people over a period of time to determine their incidence of disease. The individuals in each group are disease-free at the start of follow-up and have a common characteristic (e.g., exposed and unexposed)
selection of comparison group participantsExperimental study investigators generally use randomization to determine which individuals enter the comparison group, while cohort study investigators select a group that is as similar as possible to the exposed group. The aim with both methods is to eliminate confounding by making the groups comparable.
use of placebosIn experimental studies, placebos are used to make the experience of participating in the study comparable between the treatment and comparison groups. In cohort studies, we cannot use placebos, so we select as comparable a comparison group as possible. In both cases, the goal is to maximize the similarity between study groups in order to reduce confounding and bias.
maskingExperimental studies can be single-masked or double-masked; in cohort studies we can only mask the investigator. In both settings, the aim is to reduce bias in outcome ascertainment
(cohort study) For timingRetrospective cohort: both the exposure and the disease have already occurred at the time the study starts. Prospective cohort: the exposure has usually occurred, but the disease has not occurred at the time the study starts. Ambidirectional cohort: has both retrospective and prospective elements.
(cohort study) For feasibilitySpecial cohort: assembled to study rare exposures such as occupational exposures or unusual diets and General cohort: assembled to study common exposures; group is usually selected because they are easy to follow and are likely to give accurate data. Usually selected from a defined geographic area.
For population typeOpen or dynamic: assembled from an open or dynamic population that is defined on the basis of a changeable characteristic. Members come and go, Fixed: assembled from a fixed population that is defined on the basis of an irrevocable event. Does not gain members but losses may occur, Closed: assembled from a fixed population that is defined on the basis of an irrevocable event. Does not gain or lose members.
Advantages of prospective studiesgood data on exposures and confounders, less vulnerable to bias.
Disadvantages of prospective studiesexpensive, time-consuming, inefficient for diseases with long latent and induction period
Advantages of retrospective studiesinexpensive, fast, efficient for diseases with long latent and induction period.
Disadvantages of retrospective studiesoutcome and exposure data may be inadequate, information on confounders may be missing
Describe some population groups from which the exposed study participants might be selectedOccupational groups, groups undergoing medical treatments, groups with unusual diet/lifestyle, professional groups, students, alumni, residents in defined geographical areas
What is the main principle underlying the selection of a comparison group for a cohort study?The comparison group should be as similar as possible to the exposed group with respect to all relevant factors except the exposure itself. The ideal comparison group would consist of exactly the same individuals in the exposed group had they not been exposed. This theoretical concept is known as the counterfactual ideal. Since it is impossible for the same person to be exposed and unexposed simultaneously, epidemiologists must select different sets of people for the exposed and unexposed groups
Name and define the three types of comparison groups. Which of these is considered the “best” source for a comparison group and why?Internal is considered the best, because it will be the most comparable. Selected from the same source population as exposed group, Comparison cohort: from another similar but unexposed population, General population: from readily available data from general population, does not have information on many confounders
Name some sources of exposure information. What are some advantages and disadvantages of these?Pre-existing records: Advantages: inexpensive, no potential for recall or information bias. Disadvantages: level of detail may be inadequate or missing, information on confounders may be missing. Questionnaires, interviews: Advantages: Designed specifically for the study so good information on exposures, confounders, etc. Disadvantages: recall bias if retrospective cohort
Name some sources of outcome dataDeath certificates, medical records, questionnaires, interviews, medical exams
Describe some resources that may be used to conduct follow-upVoter registration lists; telephone books and directory assistance, Internet resources; birth, death and marriage records; drivers’ license records; hospital records; information from relatives and friends
What are the major strengths of cohort studies?Efficient for rare exposures; able to get good information on exposures, if prospective; able to evaluate multiple effects of an exposure; efficient for diseases with long induction and latent period, if retrospective; less vulnerable to bias, if prospective; clear temporal relationship between exposure and disease outcome, if prospective
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