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56 Cards in this Set
- Front
- Back
Randomized Control Trials, Cohort Studies and Case-Control Studies |
Analytic Studies |
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Cross-Sectional Studies, Ecologic Studies, Case Series and Case Reports |
Descriptive Studies |
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Disease is uncommon? |
Use case reports |
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Disease is likely caused by one exposure? |
Use case reports |
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The key outcome ofinterest can be measured better at a region or country level? |
Use Ecological studies |
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A study to look at geographic correlations? |
Use Ecological Studies |
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data collection may vary significantly between populationsor countries, making it uncertain whether comparisons are valid - which type of bias? |
Information/ measurement bias |
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Studies that are of use in assessing the impact of vaccinationprograms & screening programs?? |
Secular (time-trend) studies |
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A study that examines the relationship between diseases & other variables of interest at one particular time |
Cross-sectional studies |
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A study where it is difficult to establish whether the temporal sequence is fromthat of exposure to outcome or vice versa |
Cross-sectional studies |
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A type of observational study that comparesthe frequency of exposure to a potential risk factor among peoplewith the disease with that in a comparable group without thedisease |
Case-control |
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Important issues in case definition |
1) Case definition restrictions 2) Selection of prevalent cases vs incident cases 3) Selective survival |
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What does the validity of case-control studies depend upon? |
the comparabilityof cases & controls |
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What are the three basic principles of comparability which underlie attempts to minimizebias & confounding in selection of cases & controls? |
1- Study base 2- Deconfounding 3- Comparable Accuracy |
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Methods of control selection |
Disease-based Population-based |
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Types of matching in case-control studies |
Individual matching Frequency matching |
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Number of controls should be less than ______controls per case, why? |
5 controls per case, because there is no further gain of power above four controls per case |
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Potential problems in matching |
1) the more factors one attempts to match on, the more difficult itis to find a suitable control subject 2) Overmatching |
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Matching for an apparent confounder that actually is a result of the exposure. |
Overmatching |
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Potential biases in case-control studies |
Recall bias Selection bias Recording bias Response bias Interviewer bias |
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Which study is usually quick & therefore cheap tocarryout? |
Case-control |
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Which study can explore a range of potential causes in a single study? |
Case-control |
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Which study may be the only way of exploring causal hypotheses in rare diseases? |
Case-control |
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Which study cannot assess associations between matching variables & theoutcome? |
Case-control |
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How do we select cohorts for common exposures? |
from specialist groups |
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How do we select cohorts for rare exposures? |
from occupationalgroups & their medical records |
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three basic types of comparison cohort |
1. The general population 2. Another occupational group 3. A sub‐group of the original assumed "exposed“ cohort: those subjectsreporting no exposure form the unexposed cohort against which theremaining exposed individuals are compared |
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In which study can the temporal relationship between exposure and disease can beestablished? |
Cohort studies |
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In which study can important measures such as Attribuable Risk & Population Attribuable Risk be estimated ? |
Cohort studies |
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Which study can examine relationship between more than on disease related to a single exposure? |
Cohort studies |
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Which study is useful when exposure is rare ? |
Cohort studies |
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Which study has minimal selection & recall bias? |
Cohort studies |
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Prospective cohort studies are expensive & difficult to managebecause the involve following large numbers of people for many years |
disadvantages of cohort studies |
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Not very useful to study very rare diseases because very few exposedindividuals will develop the disease |
disadvantages of cohort studies |
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Losses to follow‐up |
disadvantages of cohort studies |
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Often requires large sample |
disadvantages of cohort studies |
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Long time to complete |
disadvantages of cohort studies |
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Exposure status can change with long follow up |
disadvantages of cohort studies |
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What expresses the frequency at which a disease occurs in a population in a specified period of time? |
Disease rate |
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The proportion (or %) of people with thedisease at a particular point in time?? |
Prevalence |
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the portion of the incidence ofa given disease in the exposed that is due to theexposure |
attributable risk |
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the percentage of theincidence rate of a given disease in theexposed group that is due (attributable) toexposure |
attributable risk percent |
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the portion of theincidence rate of a given disease in thepopulation (both exposed and non‐exposedgroups) that is attributable to the exposure |
population attributable risk |
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the incidence rate ofa disease in the population that could beeliminated if the exposure were eliminated |
population attributable risk |
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the incidence of adisease in the exposed group that would beeliminated if exposure was eliminated |
attributable risk |
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the percentage of theincidence rate of a given disease in thepopulation (both exposed & non‐exposed)that is attributable to exposure |
population attributable risk percent |
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the percentage of the incidence of adisease in the population that could beeliminated if exposure were eliminated |
population attributable risk percent |
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howrepresentative the sample is of thepopulation means |
validity |
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theability of the measure to produce thesame results under the same conditions means |
reliability |
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Which bias occurs when a researcher measuring the outcome has knowledge of the subject’sexposure to a risk factor or intervention, and this knowledge affects how they assessoutcomes? |
Observer bias |
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The impact of chance on the results of a study are usually expressed as _______ |
P values & confidence intervals |
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an event, condition, characteristic, orcombination of these factors which plays an important role inproducing the disease |
a cause |
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Factors in causation that that facilitate themanifestation of disease, disability, ill‐health, or the use of services |
Enabling factors |
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Factors in causation that are associated with thedefinitive onset of a disease; e.g. pollens in asthmatic attack |
Precipitating factors |
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Factors which aggravates an alreadyestablished disease or state. e.g. repeated exposure to a toxic agent |
Reinforcing factors |
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the process of determiningwhether observed associations are likely to be causal |
causal inference |