Lecture 2 Estimating Risk

Question 1

Define Risk

Answer 1

The likelihood that people who are exposed to a certain factor (‘risk factors’) will develop a particular disease more commonly than those who are not exposed to the stipulated ‘risk factors’

Question 2

What is a risk factor

Answer 2

A factor that is associated with higher rates of developing the disease, or which may give an indication of prognosis in disease

Question 3

What are some types of risk factors?

Answer 3

Inherited = genetics

Physical Environment = Pollution, Toxins, Mould, Dusts, Occupational exposure, etc.

Behavioural = Smoking, alcoholism, IV drug use, poor hygiene, unsafe sex, inactivity, poor diet

Social Environment = SES, overcrowding, caring for a sick spouse, bereavement, social isolation

Question 4

What is an ‘exposure’ - how is an exposure expressed?

Answer 4

‘Exposure’ refers to exposure to a risk factor

The ‘exposure’ can vary in terms of dosage, duration, number of exposures, largest dose, etc.

Exposure can take place at a single moment = E.g. exposure to infectious agent

Exposure can take place over a long period of time = E.g. long-term smokers, asbestos workers

Question 5

What factors affect recognition of risk?

Answer 5

Risk may be difficult to recognise if…

1) If there is a long latency period between the exposure and the manifestation of disease
2) If there are multiple risk factors associated with the disease
3) If the risk factor is considered ‘normal’ - it might not even be considered as something harmful and go unnoticed for a long time
4) Risk factors can predict disease, but they do not necessarily cause disease (e.g. Low SES and CVD)

Question 6

What is a ‘Marker’ of disease?

Answer 6

A marker of disease is a factor that can predict disease, but does not cause the disease. E.g. the disease will occur without it.

Question 7

What kinds of studies study risk?

Answer 7

Randomised Control Trials: Intervention Study

Observational Studies: Cohort Studies and Case-control Studies

Question 8

Describe Randomised Control Trials:

Answer 8

Are intervention studies. The participants are randomised into a treatment group and control group.

Question 9

Describe Cohort Studies

Answer 9

Are Non-interventional studies
Cohort Studies = (aka Longitudinal, Prospective, or Incident Studies)

Initially, they involve only those without the disease
Participants are followed for a length of time considered meaningful in the development of the disease
Information is gathered about their lifestyle (smoking, alcohol, employment, living situation, etc.) throughout the study
At the end, investigators calculate the incidence of the disease amongst the participants, and look for common factors in those who did vs did not develop the disease

Question 10

What is a retrospective cohort study?

Answer 10

Looking back at a group of people - perhaps a group of people who worked in a coal mine in 1966 - and do a present-day follow-up to see who has and hasn’t developed restrictive lung disease. Interview them on other relevant factors about their life as well

Question 11

What is a prospective cohort study?

Answer 11

A cohort of unaffected individuals is assembled, and a follow up is conducted a certain amount of time later, look into who did/didn’t develop the disease, and look at their lifestyle factors etc

Question 12

What is a Case Control Study?

Answer 12

Find a group of people with disease, and then match those people with unafflicted participants. Participants are matched on as many characteristics as possible - e.g. sex, age, SES, etc. Then look into the different types of exposures, or lifestyle factors that each group has, and try to identify a trend associated with risk

Question 13

How can risk be expressed and compared? And in which studies is each method used?

Answer 13

Absolute Risk and Relative Risk = used in cohort studies

Odds Ratio = used in case control studies

Question 14

What is absolute risk?

Answer 14

Used in cohort studies.

It is the incidence of a disease occurring amongst people who have been exposed

Absolute risk = (Number of exposed people who developed the disease) / (total number of exposed people)

= (exposed with disease) / (total exposed)

Question 15

What is relative risk?

Answer 15

Used in cohort studies

Measures the probability of disease occurring in exposed people, compared to the risk of disease occurring in non-exposed people

Relative risk = (Absolute Risk) / (Number of unexposed persons who developed the disease / Total number of non-exposed persons)

= (exposed with disease / total exposed) / (unexposed with disease / total unexposed)

RR = 1 - there is no association

RR = >1 - there is a positive association. Risk in exposed > risk in non-exposed

RR = higher than risk in exposed

*In the latter group, must consider if the identified exposure might actually be protective

Question 16

What is an odds ratio?

Answer 16

Used in Case-control studies

It is an equivalent of the relative risk (used in cohort studies), but of course has to be different because we start off with diseased people in case-control studies

Odds Ratio = [(number of exposed people with the disease / total number of diseased people) / (number of unexposed people with the disease / total number of diseased people)]

divided by…

[(number of exposed without disease / total number of people without the disease) / (total number of unexposed people without the disease / total number without the disease)]

Results:

OR = 1   - no association
OR = >1    -exposure is positively related to the outcome
OR = <1     - exposure is negatively related to the outcome

Question 17

Do practice questions at end of lecture on risk** Week 3

Answer 17

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