W2 what is important about measuring disease frequency?

Question 1

What is it important to measure disease frequency?

Answer 1

Understadning the size of a medical problem
Identify an outbreak
Assess risk to and management of a condition
Aids planning, what was/wasn’t successful?

Question 2

What is meant by a case definition?

Answer 2

Defining what you are measuring, e.g what are you including as a case of the illness.
Used to standardise classification.
Should include a time range, demographic, place and defining event.
Definitions should be clear measurable specific and reproducible.

Question 3

What is meant by the population at risk?

Answer 3

People who could be included among cases if they develop the case,
aka could have the disease but do not have it yet.

Question 4

What are the two types of population definitions?

Answer 4

Fixed - membership is permanent, e.g born a certain time, at a specific event
Dynamic - membership can change e.g currently working at a location or living in a certain area.

Question 5

What is the most basic epidemiological measure?

Answer 5

Count
An indicator of frequency, expressed as an integer.
5,000 people have x condition.

Question 6

How might be measure frequency?

Answer 6

Count -integer with no context
Ratio - comparitive
Proportion - has an upper limit, snapshot of at the time
Rate - no upper limit, gives idea of time

Question 7

What are the two different types of prevalence?

Answer 7

Point prevalence - the proportion of people who have a disease at any one time. (no.cases/total pop)
Period prevalence - the proportion of a population who have had a disease during a specified time period. (no.cases/total pop)

Question 8

What is prevalence useful for?

Answer 8

Determining sickness overload
Planning health servies
Examining patterns of health behaviour (lifestyle factor risk associated)

Question 9

How does disease duration affect prevalence?

Answer 9

Diseases with shorter durations are more likely to underestimate prevalence in a point prevalence as people are missed.
Longer durations = more likely overlap between cases so less likely to underestimate/

Question 10

What factors affect disease prevalence?

Answer 10

Disease duration
Case fatality
Changes in treatment/ cures
Incidence
Changing the definition of case
Migration of people between populations.

Question 11

What is incidence?

Answer 11

The number of new cases in a population at risk overtime.
Given as a proportion or a rate.

Question 12

What is the incidence proportion?

Answer 12

Also known as cumulative incidence or risk.
The number of new cases in a time period/ the number of people at risk during a time period.

Question 13

What are some pros and cons of incidence proportion?

Answer 13

Appropriate for fixed populations and short follow ups.
Not suitable for long followups when there might be a loss of subjects or the risk might change (seasonal flu)
Assume risk is the same at each check in.
Must specific time period of data collection.

Question 14

How do you calculate cumulative incidence or proportional incidence?

Answer 14

of new cases/# of population at risk

Tip #pop at risk does not include people who already have the disease.

Question 15

What should incidence and prevalence be expressed as in the final answer?

Answer 15

A percentage.

Question 16

Why is incidence proportion useful?

Answer 16

Surveillance of a disease
Understanding the aetiology of a disease
Planning a service use.

Question 17

What is incidence rate?

Answer 17

Measures the speed that new cases develop during a specified time period, also known as incidence density.

Question 18

What is meant by person time?

Answer 18

Accounts for all the time that each person in the population is a risk, is the cumulative total time in the study from all participants.
E.g ten participants in a ten year study = 100 person years.

Question 19

How do you calculate incidence rate?

Answer 19

of new cases

sum of #people*time contributed

Question 20

What is a cross sectional study?
Give an example

Answer 20

An observational study, (meaning ivestigator did not set exposure), there are comparison groups (hence is an analytical study), the exposure and the outcome of the study appear at the same time.
The percentage of people by age group in the UK who have diabetes

Question 21

What is the purpose of a cross-sectional study?

Answer 21

To give a descriptive observation on a snap shot of health in a well defined population.
Often gives a point of period prevalence.

Question 22

What are the pros and cons of a cross sectional survey?

Answer 22

+ quick and straight forwards
+ can include a large number of people
+ helps estimate the size of a problem
+ can provide variation by person, time and place
- prevalence estimates susceptibility to non-response bias
-tendency for people to include conditions with a long duration.

Question 23

What are cohort studies?
Can you give an example

Answer 23

A type of study where the investigaor does not assign exposure (observational) and there is a control group (analytical) but the exposure leads to an outcome at later date.
Following a set of children from the same town to see how many develop breast cancer later in life.

Question 24

What are the main pros and cons of a cohort study?

Answer 24

+can measure incidence
+investigate natural history and survival
+investigate multiple outcomes
+acute assessment of time-varying exposure
+easier to make a connection between temporal sequence of exposure and outcome
- expensive and time consuming
- can be limited to information on prior exposures
- inefficient for rare outcomes (often no results)
-potential selection bias, or bias by failing to check up on certain people.

Question 25

How does the influence of time show itself?

Answer 25

Period effect - a set time period has abnormal results caused by an event specific to within that time period, e.g COVID-19 pandemic decreasing breast cancer awareness
Cohort effect - variations over time in groups of people due to a shared experience e.g born in the same year, lived in the same place (north south divide in health).

Question 26

What might cause a variation in incidence?

Answer 26

New risk factor
Changes in virulence (ability for a pathogen to invade a host)
Migration between populations
Changes in intervention stratergy

Question 27

What might cause an incorrect variation in prevalence and incidence?

Answer 27

Chance
Error in data collection and coding
Error in Analysis or selective analysis.

Question 28

Draw a diagram to show how epidemiological research is subdivided.

Answer 28