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36 Cards in this Set
- Front
- Back
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Why shoudl a clinician be concerned with disease etiology
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1.prevention and
2. risk of disease 3. hunches |
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what is etiology of disease
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cause of disease, so that exposure to a causative env factor can reduced or pathogenic chain leading to development can be interrupted
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What is first step in underlying study designs
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Whether there is an association btw factor or characteristic and the development of disease. Done by studying characteristics of individuals or both
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What is second step in study designs
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derive appropriate inferences regarding a possible causal relationship from patterns of association that have been found
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WHAT IS A COHORT STUDY
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comparison of two groups for incidence of disease with an EXPOSED AND UNEXPOSED group
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what is expected if a positive association exists between exposure and disease
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expect the proportion of EXPOSED who get disease would be > proportion of NONEXPOSED group in whom disease develops
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what is incidence of disease in exposed group
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a/a + b (disease in exposed/all exposed)
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what is incidence of disease in non-exposed group
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c/c + d (disease in non-exposed/all non-exposed)
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what does incidence cases of disease show?
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new cases where there is or is not a temporal relationship btw exposure and dz
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Why must temporal relationship be established in disease?
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in order to consider exposure a possible cause of the disease in ?.
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What are two types of cohort studies?
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observational and experimental(in randomized trials)
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what is the "exposure" in randomized trials, usually
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treatment or preventive measure
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what is the essential characteristic in the design of cohort studies
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comparing outcomes in an exposed group and in an nonexposed group
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what are two basic ways to generate groups for cohort studies?
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1. create study pop based on whether or not they were exposed.
2. select defined pops before any members become exposed or before exposures are identified. |
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Describe basis of Framingham study
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select a pop on basis of some factor not related to exposure and take histories. separate pop into exposed and nonexposed groups
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What is hallmark of cohort design
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we compare exposed and non exposed persons.
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What is major problem with cohort studies
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Time of follow up is very long.
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what is a prospective cohort study or concurrent cohort or longitudinal study?
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identify group, watch for exposure, watch for result. They are concurrently followed until disease develops
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What is problem with concurrent cohort studies
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may take 20 years to complete
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what is an alternative approach using cohort design?
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RETROSPECTIVE COHORT OR HISTORICAL COHORT STUDY(also called a nonconcurrent prospective study)
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How is time shortened in a RETROSPECTIVE COHORT STUDY?
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find historical data on group from the past so to telescope frame of calendar time for study and obtain results sooner.
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What are differences in designs for prospective cohort and retrospective cohort studies
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same! studying exposed vs non exposed. Only time changes.
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Is it possible to conduct study that is combination of prospective and retrospective cohort?
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Yes, exposure is ascertained from objective records in past and follow-up and measurement of outcome continue into future.
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Describe Framingham study
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1948, 30,000, ages 30-62, CHD, 20 year follow up, , sample size of 5000.
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What was study hypothesis in Framingham study
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incidence of CHD inc with age.
Hypertense develop CHD at >rate Elev Chol leve > risk of CHD tobacco > risk of CHD Inc physical activity < risk CHD >body wt predisposes to CHD >CHD in diabetes mellitus |
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Which method did Framingham study use to select study population?
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BASED ON LOCATION of Residence - pop observed for "exposure" then determined outcome of interest (CHD)
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What can Cohort study based on defined population explore?
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MANY EXPOSURES
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What type of study was the Cowan study on late first pregnancy and breast cancer?
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combination cohort study, because compared exposed vs nonexposed. Also a retrospective study because roster came from women treated earlier for infertility.
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What kind of study is appealing for studying childhood diseases
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long term cohort studies
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What are four major questions regarding large cohort study of children?
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1. what point should individuals in cohort first be identified?
2. should cohort be draw from one center or a few or national sample? 3. how long should a cohort be followed? 4. What hypotheses and many hypotheses should be tested in cohort (significance can change over time) |
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What are major biases in cohort studies?
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1. Bias in assessment of outcome(assessing person may know of exposure, hypothesis tested, judgment may be biased by knowledge) Masking person making assessment can be addressed.
2. Information bias: if quality and extent of info obtained is diff for exp and nonexposed. Info has to be comparable in both exp and nonexposed. 3. Biases form nonresponse and losses to F/U.Exposed rates can be hard to interpret if losses occur. 4. Analytic bias: strong preconceptions by analyzers can be inferred. |
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When is a cohort study indicated on basis of information
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when exposures are suspected as possible causes of disease and are worth investigating.
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What does good evidence suggesting association of disease lead to
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cohort study is indicated.
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When is a cohort attractive to use for study
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when we can minimize attrition - thus, when incidence of exposure and development of disease is a short time.(examp - rubella and congenital malformations)
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What can make cohort design impractical?
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When strong evidence does not exist to justify expense and large study. many dz occur at low rate, so very large cohort must be enrolled for valid analysis.
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What is alternative to cohort study
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case control study.
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