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Frequency of disease Flashcards

1
Q

why should we care about disease frequency

A

to allow us to understand the size of the problem
spot outbreaks of a disease
assess risks to and management of a condition
aids planning of resources

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2
Q

case definition

A

standardised method of classifiction
exact definition depends on source of data and use

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3
Q

population at risk

A

people who would be included among the cases if they developed the disease
person time at risk

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4
Q

what does population at risk usually involve

A

place
time
demographics
defining event

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5
Q

what are the two types of population

A

fixed
dynamic

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6
Q

fixed population

A

membership is permanent
attended a specific event
born a certain time

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7
Q

dynamic population

A

membership is based current status
currently studying at uni
lives in specific city

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8
Q

most basic epidemiological measure

A

count

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9
Q

count

A

expressed as integers
answers the question “how many people have this disease?”
often the numerator of many measures
important to distinguish between incident and prevalent cases

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10
Q

limitations of count

A

doesn’t provide much information/context
pre-cursor to calculation

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11
Q

calculating a ratio

A

divide one number by the other
ranges from zero to infinity
x and y may be related or completely independent

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12
Q

calculating proportion

A

ratio where the numerator x divided by x +y
ranges from 0 to 1
often expressed as a percentage

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13
Q

calculating rate

A

expressed as x/T
T= component of time
ranges zero to infinity
measures speed at which things occur

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14
Q

prevalence

A

proportion
not a rate as no time component involved
measures proportion of existing disease in the population at a given time
dimensionless, positive number 0 to 1

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15
Q

point prevalence

A

proportion of a population who have a disease at any one time

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16
Q

point prevalence equation

A

number of cases of disease divided by the total population (cases and non-cases) at a particular point in time

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17
Q

period prevalence

A

proportion of a population who have. disease during a specified time period

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18
Q

period prevalence equation

A

number of cases of disease divided by the total population (cases and non-cases) during a period of time

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19
Q

what is the estimation of prevalence useful for

A

determination of sickness load
planning health services
examining health behaviours

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20
Q

factors affecting prevalence

A

disease duration
case fatality
changes in treatment
incidence
ascertainment of cases
migration

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21
Q

long duration

22
Q

short duration

23
Q

what are the key measures of frequency

A

prevalence
incidence

24
Q

incidence

A

measures the occurrence of new cases in a population at risk over tine
can be measures as a proportion or a rate
most fundamental epidemiological indicator:
- measures force of morbidity
- measures conversion of health status (proportion/rate)

25
measuring conversion of health status
proportion divided by rate
26
incidence proportion
proportion of people who develop a disease during a specific period of time dimensionless, positive number 0 to 1
27
incidence proportion (cumulative incidence) equation
number of new cases of disease during a specified time period divided by total population at risk during that time period
28
incidence proportion (cumulative incidence)
appropriate for fixed populations and short follow-up must specific time period of observation because risk changes with time not appropriate for long-term follow-up due to potential loss of subjects assuming: complete follow-up, same risk over time
29
cumulative incidence equation
number of new cases over a period divided by the number of population at risk over the same period
30
estimation of incidence proportion is useful for
surveillance of a disease understanding the aetiology planning service use
31
incidence rate
measures the speed that new cases develop during specified time period cases per person-time follow-up may be incomplete risk period not the same for all subjects
32
incidence rate equation
number of new cases divided by the person-time at risk during the study period
33
person-time
accounts for all the time each person is in the population at risk length of time for each person is the person-time sum of person-times is called the total person-time at risk for the population
34
investigator assigned exposures with a randomly allocated experimental study
randomised controlled trial
35
investigator assigned exposures with a non randomly allocated experimental study
non-randomised controlled trial
36
investigator didn't assign exposures with a comparison group in the observational study with an exposure to outcome direction of analytical study
cohort study
37
investigator didn't assign exposures with a comparison group in the observational study with an outcome to exposure direction of analytical study
case-control study
38
investigator didn't assign exposures with a comparison group in the observational study with an exposure and outcome at the same time direction of analytical study
cross-sectional (analytical) study
39
investigator didn't assign exposures without a comparison group in the observational study with descriptive study
cross-sectional (prevalence) study ecologic study case report/time
40
what are cross-sectional (prevalence) surveys
observational, descriptive survey of health in a ample of a well-defined population key elements: identification of target population, procedure for sampling, method of data collection, definitions used analysis: point or period prevalence estimate
41
strengths of cross-sectional prevalence surveys
quick and inexpensive potential to include large numbers useful to estimate size of the problem can describe the variation by person place and time
42
limitation of cross-sectional prevalence survey
prevalence estimates suseceptibility to non-response bias tendency to selectively include problems with long duration
43
strengths of cohort studies
can measure incidence investigate natural history and survival investigate multiple outcomes minimise recall bias accurate assessment of time-varying exposures easier to establish temporal sequence of exposure and outcome than case-control
44
limitations of cohort studies
expensive and time consuming can be limited to available information on prior exposures inefficient for rare outcomes potential selection bias
45
what are cohort studies
observational and analytical identify groups of individuals and measure exposure status starts with exposures and looks forward to possible effects
46
influence of time
period effect cohort effect
47
changes in prevalence
time of measurement change in case definition introduction or impact off an intervention or treatment changes in duration or incidence of a disease dynamic population
48
changes in incidence
new risk factor changes in virulence migration changes in intervention strategy
49
is the variation real
may be due to: chance error data collection/coding analysis
50
incidence VS prevalence
description of new cases of disease in a particular time period rate or risk of developing a disease in a specified time period requires the timing of onset of disease to be known monitoring of disease
51
prevalence VS incidence
snapshot of disease in a particular population at a point in time proportion of the population within the disease point prevalence- only suitable for disorders that persist for a reasonable Tim survey

Medicine Unit 3 (28 decks)

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