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Epidemiology > Test 2 > Flashcards

Test 2 Flashcards

1
Q

An epidemic curve is based on information about the

A

Number of new cases

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2
Q

Which of the following are frequency measures?
a.) Prevalence
b.) Birth rate
c.) Incidence
d.) Mortality

A

All of the above

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3
Q

To calculate prevalence, what should you count?

A

All cases of the disease that can be detected in the population at a time of observation

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4
Q

When measuring the disease incidence, you must count what

A

Cases of the disease that have emerged since the start and until the end of the study period in a study population

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5
Q

What is incidence rate measured as

A

New cases per animal time at risk

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6
Q

When identifying the disease status of every animal in a population at a certain time point, we are able to determine:

A

Disease prevalence

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7
Q

Prevalence is expressed as..

A

A proportion

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8
Q

In a prevalence calculation, the ‘population at risk’ in the denominator consists of

A

All animals in the group that have been investigated for the disease

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9
Q

Calculating the disease incidence rate, the population at risk is

A

All healthy individuals in an exposed population during the observation period

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10
Q

The time at risk in the context of calculating incidence rate is expressed as

A

The sum of the length of time over all healthy individuals in a population at risk, when they remained healthy

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11
Q

Observing the health status of a population of healthy animals during certain time period and registering the cases of the disease emerging during that period – which of these can we calculate?
a.) Cumulative incidence
b.) Prevalence
c.) Morbidity

A

A.) Cumulative incidence

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12
Q

Calculating the proportion of dead individuals in a population, when taking into account all death cases appearing during the observation period, we get what

A

Cumulative mortality

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13
Q

To calculate a cause specific mortality rate, we need to know what aspects

A

The size of population at risk, and number of death cases due to certain disease (cause)

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14
Q

To calculate case fatality rate, it is necessary to know what

A

Number of diseased animals and the number of animals that died due to this disease

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15
Q

Among disease frequency measures, the one having measuring unit is

A

Incidence rate

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16
Q

The static measure of the disease in a population is

A

Prevalence

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17
Q

The test used to make a decision about the status of the patient is

A

Diagnostic test

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18
Q

Test that detects secondary changes which are indirectly predicting the presence or absence of disease or the disease agent is called

A

Surrogate test

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19
Q

Tests that are aimed to discover as many potentially diseased individuals as possible in the population are classified as

A

Screening test

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20
Q

Tests for detection of agents, responses or tissue changes that are directly associated with the presence of disease are classified as

A

Pathognomonic

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21
Q

Pathognomonic test detects

A

Signs and changes directly associated with the disease

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22
Q

What does analytical specificity express

A

Frequency of cross-reactions with other substances

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23
Q

What does analytical sensitivity express?

A

Detection limit of the test

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24
Q

How do you calculate sensitivity

A

TP / (TP+FN)

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25
Q

How do you calculate accuracy?

A

(TP+TN) / (TP+FN) + (FP+TN)

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26
Q

How do you calculate specificity?

A

TN / (FP+TN)

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27
Q

Accuracy of a test expresses what?

A

Probability by which an animal’s disease status is identified by the test correctly

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28
Q

Sensitivity of a test expresses what

A

Probability by which a diseased animal is identified by the test as positive

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29
Q

Specificity of a test expresses what?

A

Probability by which a non-diseased animal is identified by the test as negative

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30
Q

How do you calculate for positive predictive value?

A

TP / (TP+FP)

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31
Q

How do you calculate for Negative predictive value?

A

TN / (FN+TN)

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32
Q

How do you calculate for apparent prevalence?

A

(TP+FP) / (TP+FN) + (FP+TN)

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33
Q

How do you calculate for true prevalence?

A

(TP+FN) / (TP+FN) + (FP+TN)

34
Q

By changing the cut off value of a test, what happens to sensitivity and specificity?

A

Both sensitivity and specificity

35
Q

When changing the cut off value increases the specificity of the test, the sensitivity of the test does what?

A

Decreases

36
Q

When combining two or more tests, the serial interpretation of test results does what?

A

Maximises the specificity of the test system

37
Q

When combining two or more tests, the parallel interpretation of test results does what?

A

Maximises the sensitivity of the test system

38
Q

What is meant by a sample?

A

Set of items or individuals selected from a larger group or population about which we wish to gather information from

39
Q

What is a sampling unit?

A
  • Object or individual that is selected from a population or group of objects individually, using some selection method
40
Q

What is a list consisting of all sampling units?

A

A frame

41
Q

The sampling frame is what

A

An individually identified population from where the sample is drawn from

42
Q

To compile a sampling frame, it is necessary to

A

Identify all diseased individuals in a population

43
Q

In case of probability sampling, by what methods are samples selected?

A

By random sampling

44
Q

The simple random sampling takes place when?

A

When every animal has an equal probability to be selected

45
Q

Cluster sampling is a sampling method where what

A

The groups of individuals are selected to be included in a study or subsets of individuals selected from those selected groups

46
Q

A random sample is also a

A

Probabilistic sample

47
Q

Systematic random sampling means that the animals are

A

Selected to the sample at certain interval

48
Q

A systematic random sample is also a

A

Probabilistic sample

49
Q

If you test only the animals who you can catch – what kind of sample is it?

A

A convenience sample

50
Q

If an investigator involves in the study population only the animals with clinical signs, the sampling method is called

A

Purposive sampling

51
Q

Stratified sampling is a sampling method where

A

Before sampling, the population is divided into subpopulations according to the factor possibly affecting the investigated parameter

52
Q

Purposive sampling is also

A

Nonprobability sampling

53
Q

Multistage sampling is a method where

A

Sample is drawn from units of different levels starting from highest

54
Q

True or false: Sample size calculations for determination of prevalence of a disease in a population does not differ from the calculation of the sample size for disease detection

A

False

55
Q

To draw a sample from a population, it is necessary to:

A

identify all individuals in a population

56
Q

The fundamental difference between explanatory/analytical and descriptive studies is that

A

Two groups of animals or farms are compared and contrasted in explanatory study

57
Q

True or false: confounding and bias are both examples of random error

A

False

58
Q

Is random allocation of animals to groups required for laboratory experiements?

A

Yes

59
Q

True or false: Laboratory experiments are usually relevant to what a clinician sees on day-to-day basis

A

False

60
Q

Pick the right one; A descriptive study..
a.) Contains a group of control animals
b.) Explains the cause of a disease in nonquantitative terms
c.) Records events without making explanatory statements

A

C. A descriptive study records events without making explanatory statements

61
Q

True or false: Misclassification bias is related to misclassification of disease and misclassification of exposure

A

True

62
Q

True or false: Conclusions about the cause of a condition can be reliably made from a case report

A

False

63
Q

Which of the following statements about surveys is true?
a.) Random and nonrandom surveys can be interpreted in same manner
b.) Most analytic techniques for surveys are based on assumption that some form of random sampling was carried out
c.) Surveys based on nonrandom samples never contain any useful information

A

B.

64
Q

To which two major types can the explanatory/analytical studies be subdivided into?

A

Experimental and observational

65
Q

Which of the following statements is false? Observational studies..
a.) Provide best information about a cause-and-effect relationship
b.) Are based on comparison of two or more groups
c.) Can be subdivided to cross-sectional, cohort and case-control studies

A

A.

66
Q

True or false: Cross sectional studies can be used to help elaborate the time ordering of a cause and disease?

A

False

67
Q

If the scales were old and consistently measure 500g too light, it may cause what kind of bias?

A

Information bias

68
Q

What can confounding be controlled by?

A

Matching by-levels of confounders
Stratifying by-levels of the confounder

69
Q

True or false: Differential misclassification occurs if the magnitude and direction of misclassification is different in the two groups being compared

A

True

70
Q

True or false: Non-differential misclassification occurs if the magnitude and direction of misclassification are similar in the two groups being compared

A

True

71
Q

Which of the statements is true: A case control study..
a.) Is often the only way to investigate the etiology of rare diseases
b.) Is usually conducted in a prospective manner
c.) Can only be used to investigate one potential cause

A

A.

72
Q

True of false:Any type of bias can affect internal and external validity of the study,

A

True

73
Q

When does unilateralism occur?

A

When factor A has no effect in the absence of factor B, but has considerable effect in the presence of B

74
Q

When does synergism occur?

A

When the effect of factor A is in the same direction, but stronger in the presence of factor B

75
Q

When does antagonism occur?

A
  • When effect of factor A works in the opposite direction when acting in the presence of factor B, to the direction in which it acts in the absence of B.
76
Q

True or false: Confounding is defined as; when the incidence rate of disease in the presence of two or more risk factors differs from the incidence rate expected to result from their individual effects

A

False

77
Q

How can information bias be controlled?

A

By increasing the accuracy of the measurements

78
Q

What does statistical significance indicate?

A

That the study results were probably not a result of chance alone

79
Q

Clinical trial and laboratory study differ from one another in a way that a clinical trial uses what kind of animals

A

Animals in their natural environment

80
Q

If the researcher only uses animals who lived in specific areas by specific roads, this leads to what kind of bias

A

Selection bias

81
Q

How can selection bias be controlled?

A

By random sampling

82
Q

If sample size was so small, and confidence intervals were wide, it is because of what kind of bias?

A

No bias

Epidemiology (3 decks)

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