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Epidemiology > L9-10 Exposure > Flashcards

L9-10 Exposure Flashcards

1
Q

Why do we measure?

To obtain quantitative data to help: (3)

A
  • Describe the distribution of disease
  • Identify determinants of health and disease
  • Identify the impact of health technologies
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2
Q

What do we measure? (4)

A
  • Attributes and statuses
  • Behaviour and events (including exposures)
  • Beliefs and knowledge
  • Attitudes, opinions and reasons
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3
Q

Read

Attributes and statuses

  • What people are:
    • Age
    • Gender
    • Marital/civil status
    • Ethnic group
    • Blood pressure, cholesterol level, other clinical parameters
    • Personal and familial medical history etc.
A
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4
Q

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Behaviour and events

  • What people do
    • Smoking
    • Food and alcohol consumption
    • Mode of travel to work etc.
  • What has happened to people
  • Being exposed to asbestos
  • Having an operation
  • Participating in health education event etc.
A
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5
Q

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Beliefs and knowledge

  • What people think is true
  • No implicit value judgement about what is good or bad
    • Knowledge of causes of disease
    • Knowledge of what constitutes ‘healthy behaviour’
    • Self-efficacy etc.
A
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6
Q

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Attitudes, opinions and reasons

  • What people say they want
  • How people feel about something
  • Essentially evaluative, largely subjective
    • Satisfaction with health care services
    • Reasons for engaging in risky behaviour
A
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7
Q

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Proxy variables

  • Often a proxy is used for the variable of real interest, if it is difficult or infeasible to measure the latter
  • Examples:
    • Body mass index for adiposity
    • Fasting insulin for insulin resistance
    • Indirect blood pressure measurement
    • Occupation or educational level for social class
A
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8
Q

How do we measure? (3)

A
  • Measuring instrument, e.g. in a hospital, workplace or the general environment
  • Recording events, e.g. treatments given
  • Responses to questionnaires, etc.
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9
Q

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Sources of measurement variation

  • Characteristics being measured (lack of constancy)
    • Subject
  • Observer (lack of objectivity)
  • Measurement procedure (lack of precision between readings or congruency between instruments)
    • Instrument or other aspects of the method of data collection
    • Assay or other aspects of analysis o Environment
A
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10
Q

Define validity.

A

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

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11
Q

Define reliability.

A

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

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12
Q

How can reliability be measured?

A

By performing two or more independent measurements and comparing the findings using an appropriate statistical test.

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13
Q

Characteristics of exposure

Define identity.

A

What the agent is (chemical, dust, physical agent, infection, etc.).

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14
Q

Characteristics of exposure

Define intensity.

A

Concentration or level of exposure.

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15
Q

Characteristics of exposure

Define duration.

A

Period of time during which the exposure occurs.

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16
Q

Characteristics of exposure

Define persistence.

A

How long agent remains in an active state in the environment or body.

17
Q

Exposure and dose definitions for individual monitoring

Define exposure.

A

Presence of a substance in the environment.

18
Q

Exposure and dose definitions for individual monitoring

Define concentration.

A

Amount of substance (often per unit of environmental medium).

19
Q

Exposure and dose definitions for individual monitoring

Define burden.

A

Amount of substance in the body (organ tissue) at a point in time (e.g from serum).

20
Q

Exposure and dose definitions for individual monitoring

Define dose.

A

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

  • Usually approximated by cumulative exposure
21
Q

Define dose reconstruction.

A

The collecting of other information to estimate the dose received.

22
Q

Define biological monitoring.

A

The measurement of exposure agents in bodily fluids or tissues.

23
Q

Read

Problems of personal level exposure assessment in epidemiology – summary

  • There may be multiple environmental media (air, water, soil, food) and multiple routes of exposure
  • It can be expensive and time consuming
  • Individual-level dosimeter measurements are often not possible; biological monitoring is the exception rather than the rule
  • There may be mixtures of exposures (e.g., contaminated water may contain metals, solvents, pesticides, microbes)
A
24
Q

Misclassification

The erroneous classification of an individual, a value, or an attribute into a ____1____ (usually disease or exposure) other than that to which it should be assigned. The term is usually applied to categorical variables but the concept is equally applicable to ____2____ variables (usually refer here to measurement error). Both ____3____ and imprecision in measurement lead to misclassification.

A
  1. Category
  2. Continuous
  3. Bias
25
Q

State and describe the types of misclassification.

A

Differential

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

Non-differential

  • The misclassification with respect to exposure (or disease) is independent of the individual’s disease (or exposure) status.
26
Q

What are the effects of differential misclassification in identifying associations between exposure & disease? (2)

A
  • Can bias results in any direction
  • May suggest an association when none is there, or vice versa
27
Q

What are the effects of non-differential misclassification in identifying associations between exposure & disease?

A

Often biases results towards the null (i.e. to diminish the magnitude of any association) – BUT NOT ALWAYS

28
Q

Minimising the impact of exposure misclassification

Differential

  • Examine whether the level of misclassification might be larger for those with higher (or lower) exposures – can any corrections be applied to these values?
  • Consider potential for bias associated with, e.g. retrospective collection of information about past events from people with and without the disease under investigation
  • Can use be made of contemporary records or measurements, rather than relying solely or largely on retrospective assessments? – BUT need to check quality of such information, including whether it is available only for a subgroup of the study population (or varies in quality across the population)

Non-differential

  • Can exposures be assessed with higher validity/reliability? (E.g. using a different type of detector?) Also need to consider costs and logistics of alternative methods of exposure assessment
  • Even if not, it would be good to assess the level of measurement variability, since this could be used to adjust analyses of the relationship between exposure and disease
A

Epidemiology (19 decks)

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