Attributes and statuses Behaviour and events Beliefs and knowledge Attitudes, opinions and reasonsW

A natural radioactive gas Comes from very small amounts of uranium that occur naturally in all rocks and soils Can be measured by placing detectors

Exposure Flashcards by Malgorzata Gorajek

What do we measure?

Attributes and statuses
Behaviour and events
Beliefs and knowledge
Attitudes, opinions and reasonsW

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What are the attributes we look into?

– Age
– Gender
– Marital/civil status
– Ethnic group
– Blood pressure, cholesterol level
– Personal and familial medical history

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What classes as behaviour?

– Smoking
– Food and alcohol consumption
– Mode of travel to work

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What is classed as an event?

– Being exposed to asbestos
– Having an operation
– Participating in health education event

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What classes of beliefs and knowledge?

– Knowledge of causes of disease
– Knowledge of what constitutes ‘healthy behaviour’
– Self-efficacy

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What classes as Attitudes, opinions and reasons?

– Satisfaction with health care services
– Reasons for engaging in risky behaviour

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What is radon?

A natural radioactive gas
Comes from very small amounts of uranium that occur naturally in all rocks and soils
Can be measured by placing detectors

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How do we measure?

Measuring instrument

Recording events

Response to questionnaires

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What are proxy variables?

Often a proxy is used for the variable of real interest, if it is difficult or infeasible to measure the latter

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What are the sources of measurement variation?

Characteristics being measured (lack of constancy)
Observer (lack of objectivity)
Measurement procedure (lack of precision between readings or congruency between instruments)

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What is validity?

The degree to which an instrument is capable of measuring accurately what it purports to measure

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What is reliability?

The degree of stability exhibited when a measurement is repeated under identical conditions

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What is TP?

True positive

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What is FP?

False Positive

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What is FN?

False-negative

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What is TN?

True negative

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What is sensitivity?

The proportion with a positive result amongst those who truly have an attribute.

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How to calculate sensitivity?

TP / (TP + FN)

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What is specificity?

Proportion with a negative result amongst those who truly do not have attribute

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How to calculate specificity?

TN / (FP + TN)

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How to calculate positive rate?

FP / (FP + TN)

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How to calculate negative rate?

FN / (FN + TP)

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What is positive predictive value?

Proportion with a true positive result amongst all those with a positive result

How is positive predictive value?

TP / (TP + FP)

What is negative predictive value?

Proportion with a true negative result amongst all those with a negative result

How to calculate predictive value?

TN / (TN + FN)

What is a screening test?

Screening tests for the presence of a condition are often based on whether or not a continuous measurement is greater than a threshold

How are screening tests examined?

A receiver operating characteristic (ROC) curve

What is a receiver operating characteristic (ROC) curve?

– a plot of sensitivity against 1-specificity – the area under the ROC curve can be used to compare different tests

What kind of validity assessments are there?

Judgement based assessment Data-based (empirical) assessments

What kinds of validity does judgement based assessment test for?

Face validity Content validity Consensual validity

What kinds of validity does data-based assessment test for?

Criterion validity Construct validity

How to measure reliability?

Reliability can be measured by performing two or more independent measurements and comparing the findings using an appropriate statistical test

What are some examples of approaches which ensure reliability?

* Standardisation and calibration * Establishment of test-retest reliability * Random allocation of subjects to observers * Multiple measurements * Importance of examining by study sub-groups

What are exposure assessment in epidemiology?

This is an important issue in both environmental and occupational studies, when examining whether there is an association between disease and prior exposure to certain agent(s)

What are the characteristics of exposure that need to be kept in mind?

* Identity * Intensity * Duration * Persistence

What is the source-pathway-receptor-model?

Hazard Exposure Body Burden Target Organ Physiological effect Clinical effect Death

What is exposure?

Presence of a substance in the environment

What is concentration?

Amount of substance

What is the cumulative exposure?

Summed amount of exposure over study period

What is a burden?

Amount of substance in the body (organ tissue) at a point in time

What is dose?

Amount of substance in the body during a specified time-interval

What are considered personal exposure measurements?

* Personal non-invasive exposure assessment * Biological monitoring * Dose reconstruction

What is biological monitoring?

The measurement of exposure agents in bodily fluids or tissues

What cautions need to be taken when using biological monitoring data?

* May only reflect recent exposure * Subject to inter-individual variation * Subject to measurement error * Can add expense, logistical problems and ethical concerns

What is dose reconstruction?

Collect other information to estimate the dose received

What are the problems of personal level exposure assessment in epidemiology?

* There may be multiple routes of exposure * It can be expensive and time-consuming * There may be mixtures of exposures

What is misclassification?

The erroneous classification of an individual, a value, or an attribute into a category other than that to which it should be assigned

What does misclassification arise from?

Bias and Imprecision

What types of misclassification is there?

Differential Non-differential

What is differential misclassification?

The misclassification with respect to exposure (or disease) is dependent on the individual’s disease (or exposure) status

What is non-differential misclassification?

The misclassification with respect to exposure (or disease) is independent of the individual’s disease (or exposure) status

How to minimise the impact of exposure differential misclassification?

Level of misclassification higher for which group? Correct this Consider potential bias Not relying solely or largely on retrospective assessments

How to minimise the impact of exposure to non-differential misclassification?

Raise the validity or reliability Assess the level of measurement variability