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HaDPop > 2.1 epidemiology > Flashcards

2.1 epidemiology Flashcards

1
Q

how can variables be divided ?

A
  • discrete (or categorical)
  • continuous
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2
Q

List categorical or discrete variables & what they are ?

A
  • nominal - categories into which individuals classified, and have no numerical relationship e.g. sex
  • ordered (ordinal) - ranking of categories e.g mild, moderate, severe
  • interval (categorical) - distance between measures on a scale that has meaning e.g. one, two people in a household
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3
Q

list continuous variables & what they are ?

A
  • Interval (continuous) - distance between measures on a scale has meaning e.g. temperature, but ratio between measurement don’t have meaning
  • ratio - distance and ratio between measurements are defined
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4
Q

What’s difference between histogram and bar chart ?

A
  • histogram - no gaps, present continuous variables
  • bar chart - has gaps, used for discrete or categorical data
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5
Q

Histogram with no gaps is used to present ?

A

continuous variables

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6
Q

To summarise properties of frequency distribution what is described ?

A
  • shape
  • location
  • spread
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7
Q

give 3 questions that can be asked with how can shape be used to describe frequency distribution ?

A
  • Is it unimodal or bimodal?
  • Is it symmetric or skewed?
  • Are there any large gaps or outliers?
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8
Q

How is location described with frequency distribution ?

A
  • mode - value which occur most often
  • median - middle value
  • mean (average) - arithmetric average
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9
Q

measures of spread describe …?

A

how variable or spread out the data are

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10
Q

IQR useful for …. distribution as it is resitant to ….

A

skewed, outliers

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11
Q
  1. What does standard deviation measure ?
  2. when is it only used ?
A
  1. spread in data around the mean
  2. when you have described the location using mean
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12
Q

workbook pg 24 Q

A
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13
Q

why is correlation coefficient used ?

A

to summarise the strength of a linear correlation

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14
Q

what’s difference between ratio and proportion ?

A
  • ratio - division of 2 unrelated numbers
  • proportion - division of 2 related numbers
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15
Q

What can rates be used to do ?

A

compare information on health and disease in different populations

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16
Q

Strictly what does a rate always imply ?

A

‘per unit time’

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17
Q

What do rates require ?

A

numerator (cases) and denominator (population) each relating to same specified time period

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18
Q

Without using rates, what may be misleading ?

A

comparisons of numbers of cases in different populations

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19
Q

what 2 concepts are included in the ‘extent od disease’ in a population ?

A

incidence & prevalence

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20
Q

relating to incidence:
1. it focuses on …?
2. numerator = ?
3. denominator = ?

A
  1. events
  2. number of new cases
  3. should only include population at risk of the disease or event
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21
Q

How may incidence be expressed as ?

A

incidence rate (a rate) or a cumulative incidence (a proportion or risk)

22
Q

what is cumulative incidence ?

A

a proportion or risk

23
Q
  1. cumulative incidence often defined as ?
  2. can be expressed as ?
A
  1. proportion of ‘at risk’ population that becomes diseased over a specified time period
  2. %
24
Q

What is calculation for incidence ?

A

number new cases in defined population over a given time / number in defined at risk population over same period of time

25
Q

Using the example of X-linked Duchenne muscular dystrophy which only affects males.

who would not be included in the ‘at risk’ population ?

A
  • females
  • people who already have the condition should also be excluded
26
Q

When reporting incidence rate what should be thought of ?

i.e. the incidence rate of meningococcal meningitis in Westminster, London (place) is 10 per 100,000 population (person) per year (time).

A

time, place, person

27
Q

what is incidence density ?

A

a specific method of calculating Incidence rate if people are followed up for different amounts of time

28
Q

which study can incidence density often occur ?

A

cohort , where particpants have differing lengths of follow-up

29
Q

calculation for incidence density ?

A

number of new cases in defined population in a specified period / total at-risk person-time of observation

30
Q

Give 4 examples of reasons why calculating the incidence is useful

A
  • measure new cases of disease when disease is of very short duration e.g. massive stroke
  • see if new cases of infectious disease are getting more frequent to see if there is an epidemic in progress
  • monitor the effect of prevention programmes
  • compare people exposed to a potential hazard with those not exposed to help determine if exposure is a real danger to health
31
Q

Calculate the total ‘at risk’ person-time of observation for the following ,

If 10 ‘at risk’ people are followed up for 5 years, 20 people are followed up for 7 years and 25 people are followed up for 10 years

A

(10 x 5) + (20 x 7) + (25 x 10) = 440 person years.

32
Q

Whilst incidence focuses on …. or …. , what does prevalence focus on ?

A

new events or cases
health status

33
Q

What is prevalence ?

A

the proportion or percentage of a population in a particular health state

34
Q

calculation for prevalence ?

A

number of cases at a given time / number of population at that time

35
Q

Why is point prevalence the most used term for prevalence ?

A

it refers to the prevalence (existing cases) at a snapshot in time

36
Q

In a population of 100,000 people there are 20,000 smokers. What’s the prevalence of smoking ?

A

20 000/ 100 000 = 20%
or 20 in 1000

37
Q

what is prevalence not ?

A

a rate

38
Q

Calculating a prevalence is useful for when ?
1. provide idea about the ….. of disease i.e extent to which disease is a …. in the community
2. know the need for particular …… which is important for planning for ….. to know how many people need …. for
3. know how many people with a ….. such as smoking is in each population

A
  1. burden, problem
  2. health services, long-standing disease, caring
  3. characteristic
39
Q

Why are prevalence and incidence related ?

A

all the prevalent cases must at some time have been incident cases,

when other things equal higher incidence ill imply higher prevalence

40
Q

Why is the relationship between incidence and prevalence not quite as simple as when other things being equal, higher incidence will imply higher prevalence ?

A

number of prevalent cases is constantly being added to by new (incident) cases, and constantly being depleted by patients dying or recovering

41
Q

What is prevalence influenced by ?

A

death rate, cure rate as well as the incidence rate

42
Q

will prevalence increase or decrease if …

new treatment is found which keeps people with the disease alive longer

A

increase

43
Q

will prevalence increase or decrease if …

more patients are cured or die

A

decrease

44
Q

Calculation that represents when the incidence rate and the rates of recovery and death are constant ?

A

P ~ (I x D)
P = prevalence
I = incidence rate
D = duration of disease

45
Q

Often morbiditiy is not as accurately recorded as … ? so…?

A

deatjs so many illness episodes are not brought to the attention of the health-care system

46
Q

morbidity rate is what ?

A

number of existing or new cases of a particular disease per 100 population (not technically always a rate)

47
Q

what’s a attack rate ?

A

number of new cases of disease that develop during a defined, short period of time per number of healthy populations at risk at the start of the period

48
Q

what’s mortality rate ?

A

a special case of an incidence rate where the event is death, rather than the onset of disease

49
Q

life expectancy = average number of …

A

years that a newborn is expected to live if current mortality rates apply

50
Q

infant mortality rate calculation ?

A

number of deaths per year occuring within first year of life x 1000 / total number of live births in the year

51
Q
A

HaDPop (13 decks)

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