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Medicine Unit 3 > Frequency of disease > Flashcards

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

A

7 months

22
Q

short duration

A

3 months

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
Q

measuring conversion of health status

A

proportion divided by rate

26
Q

incidence proportion

A

proportion of people who develop a disease during a specific period of time
dimensionless, positive number 0 to 1

27
Q

incidence proportion (cumulative incidence) equation

A

number of new cases of disease during a specified time period divided by total population at risk during that time period

28
Q

incidence proportion (cumulative incidence)

A

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
Q

cumulative incidence equation

A

number of new cases over a period divided by the number of population at risk over the same period

30
Q

estimation of incidence proportion is useful for

A

surveillance of a disease
understanding the aetiology
planning service use

31
Q

incidence rate

A

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
Q

incidence rate equation

A

number of new cases divided by the person-time at risk during the study period

33
Q

person-time

A

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
Q

investigator assigned exposures
with a randomly allocated experimental study

A

randomised controlled trial

35
Q

investigator assigned exposures
with a non randomly allocated experimental study

A

non-randomised controlled trial

36
Q

investigator didn’t assign exposures
with a comparison group in the observational study
with an exposure to outcome direction of analytical study

A

cohort study

37
Q

investigator didn’t assign exposures
with a comparison group in the observational study
with an outcome to exposure direction of analytical study

A

case-control study

38
Q

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

A

cross-sectional (analytical) study

39
Q

investigator didn’t assign exposures
without a comparison group in the observational study
with descriptive study

A

cross-sectional (prevalence) study
ecologic study
case report/time

40
Q

what are cross-sectional (prevalence) surveys

A

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
Q

strengths of cross-sectional prevalence surveys

A

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
Q

limitation of cross-sectional prevalence survey

A

prevalence estimates suseceptibility to non-response bias
tendency to selectively include problems with long duration

43
Q

strengths of cohort studies

A

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
Q

limitations of cohort studies

A

expensive and time consuming
can be limited to available information on prior exposures
inefficient for rare outcomes
potential selection bias

45
Q

what are cohort studies

A

observational and analytical
identify groups of individuals and measure exposure status
starts with exposures and looks forward to possible effects

46
Q

influence of time

A

period effect
cohort effect

47
Q

changes in prevalence

A

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
Q

changes in incidence

A

new risk factor
changes in virulence
migration
changes in intervention strategy

49
Q

is the variation real

A

may be due to:
chance
error
data collection/coding
analysis

50
Q

incidence VS prevalence

A

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
Q

prevalence VS incidence

A

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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