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ACVIM General copy > Stats/Epidemiology > Flashcards

Stats/Epidemiology Flashcards

1
Q

What is prevalence?

A
  1. The proportion of sampled individuals affected AT A GIVEN POINT IN TIME
  2. Includes both old and new cases
  3. Typically expressed as a percent
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2
Q

What is incidence?

A
  1. The number of NEW cases occurring in a specified population over a SPECIFIC PERIOD OF TIME
  2. Typically expressed as cases per individual per unit of time
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3
Q

What is the equation for prevalence in terms of a 2x2 table?

A

Prevalence = (a+c)/(a+b+c+d)

Prevalence = (animals with the disease)/(total population)

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4
Q

What is sensitivity?

A
  1. The likelihood of a POSITIVE test in individuals known to HAVE the disease
  2. The TRUE POSITIVE rate
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5
Q

What is specificity?

A
  1. The likelihood of a NEGATIVE test in individuals that DO NOT HAVE the disease
  2. The TRUE NEGATIVE rate
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6
Q

What represents the TRUE POSITIVE rate?

A

Sensitivity

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7
Q

What represents the TRUE NEGATIVE rate?

A

Specificity

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8
Q

What is the equation for sensitivity in terms of a 2x2 table?

A

Sensitivity = a/(a+c)

Sensitivity = true positives/everyone that has the disease

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9
Q

What is the equation for specificity in terms of a 2x2 table?

A

Specificity = d/(b+d)

Specificity = true negatives/everyone that does not have the disease

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10
Q

What is the positive predictive value?

A
  1. The likelihood of a POSITIVE test in an animal truly AFFECTED by the disease
  2. INCREASES as PREVALENCE of disease INCREASES
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11
Q

What is the effect on the positive predictive value as the prevalence increases?

A

The positive predictive value will increase

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12
Q

What is the negative predictive value?

A
  1. The likelihood of a NEGATIVE test in an animal truly NEGATIVE for the disease
  2. Decreases as PREVALENCE of disease INCREASES
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13
Q

What is the effect on the negative predictive value as prevalence increases?

A

The negative predictive value will decrease

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14
Q

What is the equation for positive predictive value in terms of a 2x2 table

A

PPV = a/(a+b)

PPV = true positive/all animals testing positive

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15
Q

What is the equation for negative predictive value in terms of a 2x2 table?

A

NPV = d/(c+d)

NPV = true negatives/all animals testing negative

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16
Q

What is relative risk?

A
  1. The ratio of risk in individuals exposed vs not exposed to the factor
  2. Also called risk ratio
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17
Q

What is the equation for relative risk in terms of a 2x2 table?

A

Relative risk = [a/(a+b)]/[c/(c+d)]

Relative risk = (risk in exposed individuals)/(risk in unexposed individuals)

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18
Q

Interpret:

Risk ratio = 1

A

There is no difference in risk of a given outcome between individuals exposed and unexposed to the risk factor/intervention

19
Q

Interpret:

Risk ratio < 1

A

There is less risk of the outcome in individuals exposed to the risk factor/intervention than those unexposed
*The intervention is protective

20
Q

Interpret:

Risk ratio > 1

A

There is more risk of the outcome in individuals exposed to the risk factor/intervention

21
Q

What is the odds ratio?

A
  1. The probability of an event happening vs not happening
22
Q

When is it useful to use an odds ratio?

A
  1. Useful to measure associations when INCIDENCE cannot be calculated (ie case control studies)
  2. Useful when frequency of outcome is LOW (ie would take 80 years to get a large enough population)
23
Q

What is the equation for the odds ratio in terms of a 2x2 table?

A

Odds ratio = (a x d)/(b x c)

Odds ratio = (probability that case was exposed)/(probability that a control was exposed)

24
Q

Interpret:

Odds ratio = 1

A

There is no association between the factor and the outcome

25
Q

Interpret:

Odds ratio < 1

A

There is a negative association between the factor and the outcome

26
Q

Interpret:

Odds ratio > 1

A

There is a positive association between the factor and the outcome

27
Q

What is the likelihood ratio?

A

use the sensitivity and specificity of the test to determine whether a test result usefully changes the probability that a condition (such as a disease state) exists

28
Q

What is the equation for the likelihood ratio in a positive test result?

A

Likelihood Ratio (+) = Sens/(1-spec)

29
Q

What is the equation for the likelihood ratio in a negative test result?

A

Likelihood Ratio (-) = (1-sens)/Spec

30
Q

Interpret:

Likelihood Ratio = 1

A

The test is useless

31
Q

What would be a good likelihood ratio for a positive result?

A

LR (+) > 10

32
Q

What would be a good likelihood ratio for a negative result?

A

LR (-) < 0.1

33
Q

What is a type 1 error?

A
  1. False positive rate (p-value)
  2. Rejection of a true null-hypothesis
  3. Ex: An innocent person is convicted
34
Q

What is a type 2 error?

A
  1. False negative rate
  2. Non-rejection of a false null hypothesis
  3. Ex: A guilty person is not convicted
35
Q

With a cohort study, the (relative risk/odds ratio) should be used?

A

Relative risk

36
Q

With a case control study, the (relative risk/odds ratio) should be used

A

Odds ratio

37
Q

A cohort study can be (Prospective/Retrospective/Both)

A

Both

38
Q

A case control study can be (prospective/retrospective/both)

A

Retrospective

39
Q

What does incomplete penetrance mean in terms of inheritance patterns?

A

The person either expresses the disease phenotype or they do not when they have the disease

40
Q

Incomplete penetrance is associated only with (dominant/recessive) inheritance, never (dominant/recessive) inheritance

A
  1. Dominant

2. Recessive

41
Q

A high prevalence would be indicative of a(n) (acute/chronic) disease

A

Chronic

42
Q

If the incidence is higher than the prevalence, it would be indicative of a(n) (acute/chronic) disease

A

Acute

43
Q

Disinfectants that work in the presence of organic matter

A
  1. Aldehydes
  2. Phenols
  3. Quaternary ammonium compounds (roccal)

ACVIM General copy (15 decks)

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