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Epi and Stats > Definitions > Flashcards

Definitions Flashcards

1
Q

Active Surveillance

A

The surveillance of an outcome by searching for cases in the community

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2
Q

Allocation

A

The distribution of study subjects to intervention and control arms in an intervention study

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3
Q

Allocation Concealment

A

In a randomised-controlled trial

Allocation not revealed to the person enrolling subjects to reduce selection bias

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4
Q

Alternative Hypothesis (H-Theta)

A

The opposite of the null hypothesis, but may indicate the direction of an association

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5
Q

Analytical Study

A

Designed to test a hypothesis. Generally examines whether a particular exposure is a risk factor for a particular outcome

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6
Q

Ascertainment Bias

A

A type of information bias, where detection of an outcome may vary between exposure groups. Found in intervention studies without blinding

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7
Q

Asymptomatic

A

Non-symptomatic outcome

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8
Q

Attributable Fraction

A

A measure that calculates the attributable risk as a proportion of the incidence of outcome in those exposed

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9
Q

Attributable Risk

A

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

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10
Q

Bias

A

A systematic difference from the truth

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11
Q

Blinding

A

Where information about exposure or outcome is concealed from the participants and/or observers to reduce information bias

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12
Q

Case

A

An individual that meets the case definition for having the outcome of interest

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13
Q

Case-Control Study

A

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.

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14
Q

Case Definition

A

Criteria for identifying an individual as having the health outcome of interest

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15
Q

Case-Fatality Rate

A

The proportion of cases with an outcome, which are fatal within a specified time period

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16
Q

Causal Pathway

A

The sequence of events leading from an exposure to an outcome

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17
Q

Causality

A

The relationship between an exposure and a health outcome, where the outcome is considered to be a consequence of the exposure

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18
Q

Chance

A

The possibility of observing a value or event within reason or predictability i.e. not representative

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19
Q

Cluster-Randomised Trial

A

Participants are randomised into groups rather than as individuals

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20
Q

Cohort Study

A

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

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21
Q

Compliance Risk

A

The proportion of individuals who co-operate fully

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22
Q

Component Cause

A

A factor that contributes to producing an outcome

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23
Q

Confidence Interval

A

The range of values estimated from a sample within which the ‘true’ value is likely to be found

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24
Q

Confounder

A

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

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25
Q

Confounding

A

When the association between exposure and outcome is distorted by another external factor

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26
Q

Contamination

A

Exposure of the control group to the intervention or vice versa

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27
Q

Control (Case-Control)

A

An individual that does not meet the criteria to declared a case

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28
Q

Control (Intervention)

A

A participant that does not receive the intervention

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29
Q

Cross-Sectional Study

A

Observational study that observes information on the outcome and exposure simultaneously

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30
Q

Crossover Trial

A

RCT when the participants receive both the control and intervention at different time-points acting as their own control

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31
Q

Crude Rate

A

The incidence rate in a total population, without adjustments for confounders

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32
Q

Descriptive

A

Describes existing distribution of variables in a population

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33
Q

Diagnosis

A

Classification of an outcome using rigorous tests or methods

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34
Q

Differential Misclassification

A

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

35
Q

Ecological Fallacy

A

The misleading idea that a group-level association from an ecological study can be applied at the individual level

36
Q

Ecological Study

A

An observational study in which units of analysis are population groups of people

37
Q

Effect Modification

A

Variation in effect of the exposure on an outcome across values of another factor. Detected through stratification and adjusted for statistically.

38
Q

Effect Modifier

A

Factor across whose categories the effect of an exposure on particular outcomes may vary

39
Q

Effectiveness

A

The extent to which an intervention improves a health outcome through a routine delivery system

40
Q

Elimination

A

Total removal of an outcome (usually by removal of an exposure) from a country or region

41
Q

Efficacy

A

The extent to which an intervention improves a health outcome under ideal trial conditions

42
Q

Endemic

A

Maintenance of an infection within a defined population without external influence

43
Q

Epidemic

A

Significant increase in frequency of outcome in excess of the expected frequency

44
Q

Eradication

A

Total removal of an outcome (usually by removal of an exposure) from the world

45
Q

Exclusion Criteria

A

Characteristics defining which individuals can be included in a study

46
Q

Exposed

A

Those subjects who have experienced or possess (genetic or physical characteristics) the risk factor of interest

47
Q

Exposure

A

Act of being exposed to a potential risk or protective factor

48
Q

Factorial Trial

A

RCT with more 2 or more interventions compared to the control group

49
Q

Follow-Up

A

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

50
Q

Frequency

A

A measure of the number of occurrences of an outcome per population

51
Q

General Population

A

Wider population to whom the results of analytical epidemiological studies are to be applied

52
Q

Hypothesis

A

An idea that can be tested and confirmed or denied

53
Q

Incidence

A

Number of new cases of an outcome within a defined population of individuals at risk in a specified period fo time

54
Q

Incidence Risk

A

Number of new cases of an outcome within a defined population of individuals at risk in a specified period fo time
__________________________________________
Total person-time at risk

55
Q

Incidence Risk Ratio

A

Measure of relative risk

Incidence Rate of Outcome in Exposed
_______________________________
Incidence Rate of Outcome in Unexposed

56
Q

Inclusion Criteria

A

Characteristics defining which individuals may be included in a study

57
Q

Information Bias (Measurement Bias, Assessment Bias)

A

Error due to systematic differences in the measurement or classification of participants

58
Q

Informed Consent

A

Voluntary agreement to participate in a study after being informed of the aims, methods and risks

59
Q

Intention-To-Treat Analysis

A

Subjects are analysed on the basis of initial intervention allocation irrespective of whether they complied with the allocation

60
Q

Interim Analysis

A

Independent analysis of an RCT before the planned finish in the case of safety concerns or lack of study power to detect an effect

61
Q

Intervention

A

Preventative or therapeutic measure under study in an Interventional Study. Often has an impact on the outcome

62
Q

Intervention Efficacy

A

A measure of the proportion of incidence of an outcome that can be prevented by an intervention

63
Q

Intervention Study

A

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

64
Q

Latent

A

Time between acquiring an outcome an appearance of symptoms

65
Q

Lead-Time Bias

A

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

66
Q

Length-Time Bias

A

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

67
Q

Matching

A

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)

68
Q

Minimisation

A

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

69
Q

Necessary Cause

A

A component cause that is essential for an outcome to occur

70
Q

Negative Predictive Value

A

The proportion of individuals identified as not having an outcome by not screening or diagnostic method that truly don’t have the outcome

71
Q

Nested Case-Control Study

A

Case-Control where cases and controls are identified from a prospective cohort study, reducing information bias

72
Q

Non-Differential Misclassification

A

Incorrect classification of exposure or outcome of study subjects as a result of information bias where it doesn’t vary between comparison groups

73
Q

Notifiable Disease

A

A disease that is required by law to be reported to a national database

74
Q

Null Hypothesis

A

A false hypothesis against which to test statistical data

75
Q

Observational Study

A

The Investigator observes the relationship between outcome and exposure e.g. ecological study, cross-sectional, cohort or case-control

76
Q

Observer Bias

A

Information bias introduced by measuring or assessing the outcome

77
Q

Occupational Cohort

A

A group of individuals selected for prospective study on the basis of their shared occupation

78
Q

Odds (of Exposure)

A

No. of Individuals in a defined population exposed to a particular risk factor
____________________________________________
No. of Individuals not exposed to that risk factor in the same population

79
Q

Odds (of Outcome)

A

No. of new cases that developed in a defined population in a defined time period
_____________________________________________
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

80
Q

Odds Ratio (of Exposure)

A

Odds of Exposure (Outcome)
________________________
Odds of Exposure (Non-Outcome)

Used in case-controls to calculate relative risk

81
Q

Odds Ratio (of Outcome)

A

Odds of Outcome (Exposed)
______________________
Odds of Outcome (Unexposed)

A measure of relative risk

82
Q

Outbreak

A

A sudden epidemic, usually for a short duration

83
Q

Outcome

A

A health state or event of interest e.g. infection, illness, disability or death

Epi and Stats (1 decks)

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