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RUSVM Epi Summer 17 > Measures of dz > Flashcards

Measures of dz Flashcards

1
Q

What is the most commonly-used proportion in epidemiology?

A

Prevalence

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2
Q

What type of measurement includes a fraction in which the numerator is NOT part of the denominator?

A

Ratio

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3
Q

What is a commonly-used ratio in epidemiology?

A

“The odds”
Cases: non cases
(# cases for every # non-cases)

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4
Q

What is a study population?

A

The “n” or “sample” being handled/tested

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5
Q

What is a source population?

A

The population from which the study is related to…(stray cats in Basseterre)

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6
Q

What is the target population?

A

The population that we may generalize the pattern of results
(All cats on St Kitts)

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7
Q

Measures of morbidity

A

Prevalence

Incidence

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8
Q

How is prevalence measured?

A

Proportion of the study population that is diseased at any one time;
The measure of amount of disease in the population at any one time;

Interpret as the probability of an animal from the study population BEING DISEASED

can provide information about how frequently you might expect to see the conditions in your practice

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9
Q

What is point prevalence?

A

The proportion of study population that is diseased at a SINGLE point in time

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10
Q

What is the most common measure of prevalence?

A

Point prevalence

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11
Q

How do we calculate point prevalence?

A

cases of disease present in the population at a particular time/ total population at that time

Can be expressed as a percentage, proportion, or fraction

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12
Q

What is period prevalence?

A

Proportion of population that is diseased during a specified period of time;
Measures ALL the cases of disease in the study population over a period of time;

Includes:
Old cases, new cases, but does not tell us WHEN the animals became diseased…

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13
Q

How do we calculate period prevalence?

A

cases of disease present in the population (OVER A PERIOD OF TIME) / total population over that period of time

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14
Q

What is incidence?

A

The number of NEW cases of disease that occur in the study population over time;

The probability of a disease-free animal from the study population becoming diseased…

AKA THE RISK OF BECOMING DZ’d

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15
Q

Cumulative incidence is ?

A

Proportion of disease-free (susceptible) individuals in the study population who became diseased during a specified period of time

*can be interpreted as the probability of becoming Dz’d during the study time period

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16
Q

How do we cumulative calculate incidence?

A

NEW cases of disease in a population over a specified time period / total population at RISK at the start time of the time period

17
Q

How can cumulative incidence be expressed?

A
  • a number (with reference to time and population at risk)

- a dimensionless fraction with reference to time

18
Q

What are the assumptions that come with cumulative incidence?

A
  1. All individuals in the study population are at risk of getting disease
  2. Every individual in study population is assessed at the start of the study, to identify and remove EXISTING cases
  3. The ENTIRE population at risk must be followed from the start of the study until the end
19
Q

What is attack rate?

A

A specific type of cumulative incidence;

Cumulative incidence DURING an outbreak

Applied to a narrowly-defined population, observed for a limited period of time

20
Q

How can we interpret attack rate incidence?

A

The probability (risk) of becoming diseased DURING the course of an outbreak

21
Q

How do we calculate attack rate?

A

new cases in a population over a specified time period / total population at risk (exposed) at the start of the time period

22
Q

What is the incidence rate?

A

The instantaneous rate of occurrence of new cases of disease among NON-diseased animals in the population

aka incidence density

23
Q

What is the drawback of incidence rate?

A

Cannot easily interpret incidence rate at the INDIVIDUAL animal level

24
Q

How do we calculate incidence rate?

A

new cases of disease in a population over a specified time period / SUM of the length of time during which each individual in the population is at risk

25
Q

How is incidence rate expressed?

A

cases / animal-time at risk

Ex) 15 cases per 100 cow-months at risk

26
Q

Anything that affects the ______ of disease will affect prevalence

A

Duration

27
Q

Anything that affects the _______ can influence the prevalence.

A

Change in # of new cases

28
Q

What are some benefits of prevalence over incidence?

A

Reflects the overall magnitude of a disease; is the best measure to assess the overall burden of the disorder (including costs and resources)

29
Q

What is the case-fatality rate?

A

of cases of a specific disease that are fatal, within a specified time following disease onset

30
Q

How is case-fatality rate calculated?

A

cases of disease that die in a specified time period following disease onset / total number of individuals with the disease

31
Q

When measuring disease occurrence it is important to clearly define what 4 things?

A
  1. what is being measured (dz, infection, etc)
  2. The persons or animals included in the measurement
  3. Place or location of the study population
  4. Time period of the study
32
Q

What are the 4 most common types of measures in epidemiology?

A
  1. counts
  2. proportions
  3. ratios
  4. rates
33
Q

All other measures of disease occurrence are based on _____, but on their own, they convey little information

A

Counts

34
Q

The count of animals with the disease (being measured), as a fraction of the total animals that COULD be diseased is known as the __________

A

Proportion

In a proportion, animals in the numerator are included in the denominator. These are often expressed at fractions or percentages

35
Q

T/F: The prevalence of a dz may increase when incidence remains stable but survival cases improve

A

TRUE

Since prevalence includes all cases - new and old. When older cases live longer = increase prevalence

36
Q

Incidence is generally used for more ____ diseases

A

acute

  • used to assess causes for dz
  • best measure to assess increasing or decreasing trends in dz frequency
37
Q

What is a cause-specific mortality rate? How is it calculated?

A

The mortality rate due to a specific disease or event

of deaths from a specific dz/even during a specified time period / Total population during that same time period

RUSVM Epi Summer 17 (29 decks)

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