Prognosis

Question 1

What is prognosis?

Answer 1

An assessment of the future course and outcome of a patient’s disease, based on knowledge of the course of disease in other patients together with the general health, age, and sex of the patient

Question 2

What are prognostic factors?

Answer 2

Certain patient characteristics can predict outcomes more accurately

Question 3

What are risk factors?

Answer 3

Patient characteristics associated with the development of the disease in the first place.

Question 4

Why is prognosis important? (2)

Answer 4

• Helps in treatment decision making
• Helps in discussing the opinions of patients or relatives concerning management

Question 5

What are the types of prognosis questions? (3)

Answer 5

• Which outcomes could happen? (qualitative aspect)
• How likely are the outcomes to happen? (quantitative aspect)
• Over what period will the outcomes happen? (temporal aspect)

Question 6

What are the most appropriate studies to measure prognosis? (2)

Answer 6

• Cohort
• Case-control

Question 7

Why are RCTs inappropriate to measure prognosis?

Answer 7

It is not appropriate to randomise patients to different prognostic factors

Question 8

How are cohort studies used in selecting the study population? (2)

Answer 8

• Recruit individuals with the disease who are exposed to the possible prognostic factor
• Compare group with disease with group without disease

Question 9

What type of bias can cohort studies produce?

Answer 9

Selection bias

Question 10

How do we collect data in cohort studies? (2)

Answer 10

• Baseline data/Record of exposure
• Follow-up data

Question 11

What is needed in the follow up of cohort studies? (4)

Answer 11

• Needs to be long enough to identify outcome of interest
• Need to maximise completeness
• If too many participants lost at follow-up, results could be biased
• To reduce potential for bias

Question 12

What is needed in the interpretation of cohort studies? (2)

Answer 12

• Provides evidence of association does not cause
• Need to be aware of possible bias

Question 13

What are the strengths of cohort studies? (6)

Answer 13

• Useful for investigating the natural history and incidence of a disease
• Useful for investigating multiple outcomes
• Useful in the study of rare exposures
• Allows calculation of useful estimates (including incidence rates, relative risks, and confidence intervals)
• Historical cohort studies are effective in the investigation of diseases that have a long development time
• Reduces risk of survivor bias (a failure to consider those without the outcomes of interest)

Question 14

What are the weaknesses of cohort studies? (4)

Answer 14

• Can be expensive and time consuming
• Attrition bias -Loss to follow up can be a difficulty. There could be significant differences in the loss to follow between both groups.
• Susceptible to selection bias
• Recall bias is very minimal in cohort studies, and many results can be studied at the same time.

Question 15

What is attrition bias?

Answer 15

Systematic differences between people who leave the study and those who continue.

Question 16

What is selection bias?

Answer 16

Enrolling an exposed person if they have the outcome of interest, the measure of association will be biased

Question 17

What are the strengths of case control studies? (5)

Answer 17

• Effective in the investigation of diseases that have a long development time
• Useful in the study of rare diseases
• Allows calculation of useful estimates (including incidence rates, odds ratios, and confidence intervals)
• Can study multiple risk factors/exposures
• Most efficient use of resources (money, time and effort)

Question 18

What are the weaknesses of case control studies? (3)

Answer 18

• If the frequency of the exposure is low, case-control studies quickly become inefficient
• Can be difficult to choose an appropriate control group
• Susceptible to selection and recall bias

Question 19

How can prognostic evidence be presented? (3)

Answer 19

• Median survival
• Percentage of survival/specified outcome at a particular point in time
• Survival curves

Question 20

What is a survival curve?

Answer 20

Depict at each point in time the proportion (expressed as a percentage) of the original sample who have not yet died/experienced the outcome

Question 21

What is a median survival?

Answer 21

The length of follow-up by which 50% of study patients have died/experienced the outcome (e.g. at least half of all patients with this disease survive 5 years)