2.1 epidemiology

Question 1

how can variables be divided ?

Answer 1

• discrete (or categorical)
• continuous

Question 2

List categorical or discrete variables & what they are ?

Answer 2

• 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

Question 3

list continuous variables & what they are ?

Answer 3

• 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

Question 4

What’s difference between histogram and bar chart ?

Answer 4

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

Question 5

Histogram with no gaps is used to present ?

Answer 5

continuous variables

Question 6

To summarise properties of frequency distribution what is described ?

Answer 6

• shape
• location
• spread

Question 7

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

Answer 7

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

Question 8

How is location described with frequency distribution ?

Answer 8

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

Question 9

measures of spread describe …?

Answer 9

how variable or spread out the data are

Question 10

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

Answer 10

skewed, outliers

Question 11

1. What does standard deviation measure ?
2. when is it only used ?

Answer 11

1. spread in data around the mean
2. when you have described the location using mean

Question 12

workbook pg 24 Q

Question 13

why is correlation coefficient used ?

Answer 13

to summarise the strength of a linear correlation

Question 14

what’s difference between ratio and proportion ?

Answer 14

• ratio - division of 2 unrelated numbers
• proportion - division of 2 related numbers

Question 15

What can rates be used to do ?

Answer 15

compare information on health and disease in different populations

Question 16

Strictly what does a rate always imply ?

Answer 16

‘per unit time’

Question 17

What do rates require ?

Answer 17

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

Question 18

Without using rates, what may be misleading ?

Answer 18

comparisons of numbers of cases in different populations

Question 19

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

Answer 19

incidence & prevalence

Question 20

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

Answer 20

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

Question 21

How may incidence be expressed as ?

Answer 21

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

Question 22

what is cumulative incidence ?

Answer 22

a proportion or risk

Question 23

1. cumulative incidence often defined as ?
2. can be expressed as ?

Answer 23

1. proportion of ‘at risk’ population that becomes diseased over a specified time period
2. %

Question 24

What is calculation for incidence ?

Answer 24

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

Question 25

Using the example of X-linked Duchenne muscular dystrophy which only affects males. who would not be included in the 'at risk' population ?

Answer 25

* females * people who already have the condition should also be excluded

Question 26

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).

Answer 26

time, place, person

Question 27

what is incidence density ?

Answer 27

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

Question 28

which study can incidence density often occur ?

Answer 28

cohort , where particpants have differing lengths of follow-up

Question 29

calculation for incidence density ?

Answer 29

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

Question 30

Give 4 examples of reasons why calculating the incidence is useful

Answer 30

* 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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

new events or cases health status

Question 33

What is prevalence ?

Answer 33

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

Question 34

calculation for prevalence ?

Answer 34

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

Question 35

Why is point prevalence the most used term for prevalence ?

Answer 35

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

Question 36

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

Answer 36

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

Question 37

what is prevalence not ?

Answer 37

a rate

Question 38

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

Answer 38

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

Question 39

Why are prevalence and incidence related ?

Answer 39

all the prevalent cases must at some time have been incident cases, when other things equal higher incidence ill imply higher prevalence

Question 40

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

Answer 40

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

Question 41

What is prevalence influenced by ?

Answer 41

death rate, cure rate as well as the incidence rate

Question 42

will prevalence increase or decrease if ... new treatment is found which keeps people with the disease alive longer

Answer 42

increase

Question 43

will prevalence increase or decrease if ... more patients are cured or die

Answer 43

decrease

Question 44

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

Answer 44

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

Question 45

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

Answer 45

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

Question 46

morbidity rate is what ?

Answer 46

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

Question 47

what's a attack rate ?

Answer 47

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

Question 48

what's mortality rate ?

Answer 48

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

Question 49

life expectancy = average number of ...

Answer 49

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

Question 50

infant mortality rate calculation ?

Answer 50

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