Definitions Flashcards
Active Surveillance
The surveillance of an outcome by searching for cases in the community
Allocation
The distribution of study subjects to intervention and control arms in an intervention study
Allocation Concealment
In a randomised-controlled trial
Allocation not revealed to the person enrolling subjects to reduce selection bias
Alternative Hypothesis (H-Theta)
The opposite of the null hypothesis, but may indicate the direction of an association
Analytical Study
Designed to test a hypothesis. Generally examines whether a particular exposure is a risk factor for a particular outcome
Ascertainment Bias
A type of information bias, where detection of an outcome may vary between exposure groups. Found in intervention studies without blinding
Asymptomatic
Non-symptomatic outcome
Attributable Fraction
A measure that calculates the attributable risk as a proportion of the incidence of outcome in those exposed
Attributable Risk
A measure that calculates the additional incidence of outcome in those exposed after subtracting the incidence that would have occurred in the absence of exposure i.e. no. of cases that could be prevented if the exposure was completely eliminated
Assumes the link is causal
Can be calculated from risks or incidence rates
Bias
A systematic difference from the truth
Blinding
Where information about exposure or outcome is concealed from the participants and/or observers to reduce information bias
Case
An individual that meets the case definition for having the outcome of interest
Case-Control Study
An observational study in which 2 groups are defined on the basis of their outcome status (cases have exposure, controls don’t).
Levels of exposure to a risk factor is then measured between the groups and compared.
Odds ratio is the only measure or relative risk that can be obtained from case-control studies. No measure of the frequency of the outcome.
Case Definition
Criteria for identifying an individual as having the health outcome of interest
Case-Fatality Rate
The proportion of cases with an outcome, which are fatal within a specified time period
Causal Pathway
The sequence of events leading from an exposure to an outcome
Causality
The relationship between an exposure and a health outcome, where the outcome is considered to be a consequence of the exposure
Chance
The possibility of observing a value or event within reason or predictability i.e. not representative
Cluster-Randomised Trial
Participants are randomised into groups rather than as individuals
Cohort Study
An observational study in which two groups are defined on the basis of their exposure to a potential risk factor over time to measure the incidence of the outcome which is then compared to give an estimate of relative risk
Compliance Risk
The proportion of individuals who co-operate fully
Component Cause
A factor that contributes to producing an outcome
Confidence Interval
The range of values estimated from a sample within which the ‘true’ value is likely to be found
Confounder
A variable that is associated with both the exposure and outcome but it not in the causal pathway that is being investigated and may provide an alternative explanation for any association observed
Confounding
When the association between exposure and outcome is distorted by another external factor
Contamination
Exposure of the control group to the intervention or vice versa
Control (Case-Control)
An individual that does not meet the criteria to declared a case
Control (Intervention)
A participant that does not receive the intervention
Cross-Sectional Study
Observational study that observes information on the outcome and exposure simultaneously
Crossover Trial
RCT when the participants receive both the control and intervention at different time-points acting as their own control
Crude Rate
The incidence rate in a total population, without adjustments for confounders
Descriptive
Describes existing distribution of variables in a population
Diagnosis
Classification of an outcome using rigorous tests or methods
Differential Misclassification
Differing incorrect classifications of either the exposure or outcome subjects as a result of information bias. Can lead to over or under-estimation of associations
Ecological Fallacy
The misleading idea that a group-level association from an ecological study can be applied at the individual level
Ecological Study
An observational study in which units of analysis are population groups of people
Effect Modification
Variation in effect of the exposure on an outcome across values of another factor. Detected through stratification and adjusted for statistically.
Effect Modifier
Factor across whose categories the effect of an exposure on particular outcomes may vary
Effectiveness
The extent to which an intervention improves a health outcome through a routine delivery system
Elimination
Total removal of an outcome (usually by removal of an exposure) from a country or region
Efficacy
The extent to which an intervention improves a health outcome under ideal trial conditions
Endemic
Maintenance of an infection within a defined population without external influence
Epidemic
Significant increase in frequency of outcome in excess of the expected frequency
Eradication
Total removal of an outcome (usually by removal of an exposure) from the world
Exclusion Criteria
Characteristics defining which individuals can be included in a study
Exposed
Those subjects who have experienced or possess (genetic or physical characteristics) the risk factor of interest
Exposure
Act of being exposed to a potential risk or protective factor
Factorial Trial
RCT with more 2 or more interventions compared to the control group
Follow-Up
Observation over a period of time of an individual, group or initially defined population whose relevant characteristics have been assessed to observe changes in exposures or outcomes
Frequency
A measure of the number of occurrences of an outcome per population
General Population
Wider population to whom the results of analytical epidemiological studies are to be applied
Hypothesis
An idea that can be tested and confirmed or denied
Incidence
Number of new cases of an outcome within a defined population of individuals at risk in a specified period fo time
Incidence Risk
Number of new cases of an outcome within a defined population of individuals at risk in a specified period fo time
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Total person-time at risk
Incidence Risk Ratio
Measure of relative risk
Incidence Rate of Outcome in Exposed
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Incidence Rate of Outcome in Unexposed
Inclusion Criteria
Characteristics defining which individuals may be included in a study
Information Bias (Measurement Bias, Assessment Bias)
Error due to systematic differences in the measurement or classification of participants
Informed Consent
Voluntary agreement to participate in a study after being informed of the aims, methods and risks
Intention-To-Treat Analysis
Subjects are analysed on the basis of initial intervention allocation irrespective of whether they complied with the allocation
Interim Analysis
Independent analysis of an RCT before the planned finish in the case of safety concerns or lack of study power to detect an effect
Intervention
Preventative or therapeutic measure under study in an Interventional Study. Often has an impact on the outcome
Intervention Efficacy
A measure of the proportion of incidence of an outcome that can be prevented by an intervention
Intervention Study
A study designed to test if there is a causal relationship by reducing/removing exposure to a risk factor or improving/introducing exposure to a protective factor and observing the outcome
Latent
Time between acquiring an outcome an appearance of symptoms
Lead-Time Bias
Time difference between detection of an outcome or risk factor and the appearance of symptoms that may lead to an apparent increase in survival time even if there is no effect on the outcome
Length-Time Bias
Time difference in the length of time taken for an outcome to progress to severe effects that may affect the apparent efficacy of a screening method
Matching
A technique used to control confounding during study design. The comparison groups are selected to have the same distribution of potential confounders by matching individually (pair matching) or groups (frequency matching)
Minimisation
Method of allocation that aims to minimise difference between intervention and control arms in small RCTs where there may be several confounders or effect modifiers
Necessary Cause
A component cause that is essential for an outcome to occur
Negative Predictive Value
The proportion of individuals identified as not having an outcome by not screening or diagnostic method that truly don’t have the outcome
Nested Case-Control Study
Case-Control where cases and controls are identified from a prospective cohort study, reducing information bias
Non-Differential Misclassification
Incorrect classification of exposure or outcome of study subjects as a result of information bias where it doesn’t vary between comparison groups
Notifiable Disease
A disease that is required by law to be reported to a national database
Null Hypothesis
A false hypothesis against which to test statistical data
Observational Study
The Investigator observes the relationship between outcome and exposure e.g. ecological study, cross-sectional, cohort or case-control
Observer Bias
Information bias introduced by measuring or assessing the outcome
Occupational Cohort
A group of individuals selected for prospective study on the basis of their shared occupation
Odds (of Exposure)
No. of Individuals in a defined population exposed to a particular risk factor
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No. of Individuals not exposed to that risk factor in the same population
Odds (of Outcome)
No. of new cases that developed in a defined population in a defined time period
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No. of individuals who do not develop the outcome during the same time-period
Can be interpreted as the ratio of the risk that the outcome will occur to the risk that it will not occur during a specified period of time
Odds Ratio (of Exposure)
Odds of Exposure (Outcome)
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Odds of Exposure (Non-Outcome)
Used in case-controls to calculate relative risk
Odds Ratio (of Outcome)
Odds of Outcome (Exposed)
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Odds of Outcome (Unexposed)
A measure of relative risk
Outbreak
A sudden epidemic, usually for a short duration
Outcome
A health state or event of interest e.g. infection, illness, disability or death
