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Epi > Block 5 > Flashcards

Block 5 Flashcards

1
Q

Clinical approach focuses on _____ and Epidemiological approach focuses on _____

A

Individuals; Population

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2
Q

Success of clinical approach depends on… (2)

A
  • Etiology being known
  • Correct diagnosis or correct list of diagnoses
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3
Q

Success of epidemiological approach….

A

Can be achieved without knowing the etiological agent or mechanism of action between exposure and disease

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4
Q

Clinical approach

A

Establish a diagnosis or small list of possible diagnoses: physical exam and history, generate list of ddxs, further examination and diagnostic testing. Treat against the diagnosis or list of diagnoses.

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5
Q

Epidemiological approach (4)

A

1) Describe the occurance of disease in populations.
2) Look for differences in disease occurance between groups in populations (groups with vs without certain exposures).
3) Identify those exposures that cause disease.
4) Apply measures to reduce those exposures.

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6
Q

Population

A

A defined collection of individuals who share one or more observable characteristics, as specified in the definition.

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7
Q

Descriptive Epidemiology

A

Describe the health status of specified populations

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8
Q

Study design of descriptive epidemiology

A

Surveys – goals is to estimate, with some defined precision, the frequency and distribution of selected outcomes in a defined population, based on measurements in a sample of that population

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9
Q

Analytical Epidemiology (3)

A

1) Epidemiologic research to identify potential causal associations between exposures and health-related outcomes.
2) The aim is to make causal inferences about relationships between exposure and disease.
3) Scientific process to seek understanding of a phenomenon.

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10
Q

Census vs Sample

A

Census = every individual in the population is evaluated
Sample = only a subset of individuals drawn from the population are evaluated (more feasible than a census)

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11
Q

Sampling

A

The process of selecting study subjects

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12
Q

What source of error does sampling introduce into epi studies

A

Sampling variability/random error

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13
Q

The opposite of random error is _____

A

Precision (an estimate with little random error may be described as precise)

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14
Q

Precision can be improved by ______

A

Increasing the sample size

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15
Q

Statistical inference

A

The process of drawing conclusions about a population based on data from a sample of that population. It allows us to deal with random error.

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16
Q

What is the only source of error in epidemiological studies?

A

Random error

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17
Q

Bias occurs due to _____

A

systematic error

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18
Q

Extent of bias (can/cannot) be determined

A

Cannot; there is no formal method to deal with systematic error (as there is with random error).

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19
Q

Probability sampling methods (4)

A

1) Simple random sampling
2) Systematic random sampling
3) Stratified random sampling
4) Cluster sampling

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20
Q

Simple random sampling

A

Each subject in the population has an equal chance of being selected. Requires a sampling frame of all subjects in the population (disadvantage).

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21
Q

Systematic random sampling

A

Doesn’t require sampling frame, only an estimate of the total population size and a means of sampling subjects at a predefined interval.

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22
Q

Stratified random sampling

A

Prior to sampling, divide populations into mutually exclusive strata (=groups) based on factors likely to affect disease occurrence (eg sex, breed..). Within each stratum, select a sample (simple or systematic random sample).

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23
Q

Advantages of stratified random sampling (3)

A

1) Ensures that all strata are represented in sample
2) May increase precision of overall estimates
3) Produces estimates of stratum-specific disease occurrence

24
Q

Cluster sampling

A

A cluster is a natural collection of study subjects (eg farm, herd, litter, pen…)

25
Q

One stage cluster sampling

A

Randomly select clusters, and sample all subjects within selected clusters

26
Q

Two stage cluster sampling

A

Randomly select clusters, then randomly select subjects from within those clusters

27
Q

Advantages of cluster sampling (2)

A

1) Only need sampling frame of clusters (eg all farms in district).
2) May be more cost-effective than simple random sampling.

28
Q

Point estimate

A

Use the sample data to calculate a single number to estimate the proportion of diseased animals in the population

29
Q

Interval estimate

A

Use the sample data to calculate a range of reasonable values that are intended to contain the true proportion of diseased animals in the population. This method accounts for random error and provides an indication of the precision of our estimate.

30
Q

Problem with point estimate

A

Does not account for random error

31
Q

Prevalence

A

The proportion of the population that is diseased

32
Q

Point prevalence

A

The proportion of the population with the disease/condition at a single point in time

33
Q

Period prevalence

A

The proportion of the population with the disease/condition over a specific period of time

34
Q

T/F: Period prevalence does not distinguish existing cases from new cases

A

True

35
Q

Factors that increase prevalence (6)

A

1) Increase in new cases
2) Longer duration of disease
3) Prolongation of life without cure
4) In-migration of cases
5) Out-migration of health animals
6) Improved diagnostics

36
Q

Factors that decrease prevalence (6)

A

1) Decrease in new cases
2) Shorter duration of disease
3) High case-fatality rate from disease
4) In-migration of health animals
5) migration of cases
6) Improved cure rate

37
Q

Incidence

A

Measures how frequently susceptible individuals become diseased as they are observed over time

38
Q

Incidence risk can only be measured in what type of population?

A

Closed population (no additions to the population and no (or only few) losses over the period of the study; the entire population at risk must be followed from the start of the study until the end)

39
Q

Incidence rate is expressed as:

A

The number of cases per animal-time unit at risk

40
Q

Incidence rate can be measured in ____ populations

A

Open (animals are entering and leaving the population throughout the study period).

41
Q

Prevalence is a function of…

A

Incidence (rate at which new cases arise) and Duration of Disease (which is determined by the rate at which existing cases of disease become non-cases, by dying or being cured).

42
Q

Attack rate

A

Incidence risk during an outbreak

43
Q

When would you use an attack rate

A

When period of risk is limited and any cases arising from exposure are likely to occur in the risk period

44
Q

Mortality risk/rate

A

Incidence risk/rate where death is the outcome of interest

45
Q

Cause-specific mortality risk/rate

A

Mortality risk/rate due to a specific disease/event

46
Q

Case-fatality rate

A

Proportion of cases of a specific disease that are fatal, within a defined time period following disease onset or diagnosis.

47
Q

Exposure

A

Any potential determinant of disease or health status (pathogen, toxin, host factors, env factors….).
An exposure may increase or decrease the occurrence of disease OR have no effect at all.
Once an exposure is shown to be associated with the disease, it is a determinant (a risk/protective factor–not necessarily causal).

48
Q

Once an exposure is shown to be associated with the disease, it is a _____

A

Determinant (a risk/protective factor–not necessarily causal)

49
Q

Outcome

A

A result or response, usually a disease or some other change in health status.

50
Q

There is an association between an exposure and a disease if (3):

A

1) The proportion of individuals with the disease is significantly higher (+ve) or lower (-ve) in those exposed than in those who are not exposed
2) The number of new cases of disease that arise over a specified time period is significantly higher (+ve) or lower (-ve) in those exposed than in those who are not exposed
3) Exposure is significantly more common (+ve) or less common (-ve) in those with the disease than in those without the disease

51
Q

What are measures of association? And what two things do they do?

A

Used to assess the magnitude of the relationship between an exposure and the disease of interest in the population.
They 1) determine if there is an association, and 2) measure the strength of the association

52
Q

How are measures of association expressed

A

As a relative measure calculated as the ratio of two estimates of disease occurence

53
Q

If the measure of association = 1

A

There is no association (measure of occurrence is the same in both groups)

54
Q

If the measure of association > 1

A

There is a positive association between exposure and disease. Exposure is a ‘risk factor’ for disease (not necessarily causal).

55
Q

If the measure of association < 1

A

There is a negative association between exposure and disease. Exposure is a ‘protective factor’ for disease (not necessarily causal).

Epi (3 decks)

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