Ways of expressing prognosis

Question 1

Prognosis

Answer 1

is the likely course or outcome of a disease and includes the chance of recovery from an illness

Question 2

Natural history

Answer 2

stages of a disease that occur in an individual

Question 3

Prognosis may be expressed in terms of:

Answer 3

death
survivors of disease
interval from diagnosis to reoccurrence of disease
diagnosis to time of functional impairment disability
changes in patients quality of life

Question 4

When assessing prognosis, at what point do we begin to quantify survival time?

Answer 4

ideally From time of disease onset but people will only become aware that they are ill once they have symptoms
Time of diagnosis: there is variability because time of diagnosis is not the time at which patient first became ill

Question 5

Why is it valuable to know the prognosis of a disease?

Answer 5

• if severity is known then priorities for clinical services and public health programmes can be established
• patient often ask questions about prognosis
• if the normal disease process and chance of survival is known then the effect of treatment can be compared to expected outcome w/out treatment
• effectiveness of new and diff types of treatments can be compared with one another and with older treatment regimes

Question 6

Expressing prognosis/ measure of prognosis

Answer 6

• case fatality rate
• person years
• five-year survival rate
• observed survival rate
• median survival rate
• relative survival rate

Question 7

Case fatality rate

Answer 7

short term, acute diseases

no. of people who die from the disease/ no. of people who have the disease

Question 8

Person years

Answer 8

measurement that combines no. of years that each person in a study was at risk of getting a particular disease but did not get the disease and was observed.
Formula: sum of the no. of years each person was at risk of getting a specific condition
most often used when determining incidence rates

Question 9

Five-year survival

Answer 9

% of patients who are still alive 5 years after diagnosis or treatment begins. Often used in clinical medicine with regard to cancer treatments.
Most deaths from cancer take place during the five year period after diagnosis.
Influenced by time of diagnosis

Question 10

Observed survival

Answer 10

based on knowing the interval within which the event occurred
expresses prognosis using life tables
A life table is a statistical table which gives the survival data for a group of individuals

Question 11

Life table calculations include

Answer 11

• no. of people alive and under observation at the beginning of each interval
• no. of people dying at each interval
• no. of people lost to follow up each interval
• conditional probability of survival of each interval
• cumulative probabilities of survival from the beginning of study to end of study

Question 12

Kaplan -meier method

Answer 12

the exact time of death are recorded

Question 13

Two assumptions when using life tables

Answer 13

• there has been no change in effectiveness of treatment or survival during the time of study
• effectiveness of treatment or survivorship of people who are lost to follow up is the same as the experience of those who are followed up

Question 14

Median survival time

Answer 14

length of time that half of the study population survives

Question 15

Two advantages over mean survival time

Answer 15

• less affected by extremes
• to calculate median survival we only have to observe the deaths of half the study group but to calculate the mean survival we have to observe the death of the entire group

Question 16

Relative survival rate

Answer 16

ratio

observed survival in people with the disease/ expected survival if disease were absent