WEEK 2: PROGNOSIS

Question 1

Define prognosis

Answer 1

A prediction of the progress or outcome of a disease
A prediction of the course and likely outcome of a disease

Question 2

What are the importance of prognosis?

Answer 2

Patient/ family counseling
Financial issues
Planning for the future
Helps doctors and patients in joint decision making on treatments
Need for quantity
Development and evaluation of interventions

Question 3

How is prognosis measured in clinicals?

Answer 3

Biological onset of the disease
Pathologic evidence of disease
Signs and symptoms
Medical care sought
Diagnosis
Treatment

Question 4

What is time zero?

Answer 4

When the disease started

Question 5

How can time zero determined?

Answer 5

Using time for
*First symptoms
*First detection
*First diagnosis

Question 6

What are the 4 D’s for prognosis outcome ?

Answer 6

Distress (pain, other symptoms)

Disease (cure, remission, recurrence, progression)

Disability (physical, mental)

Death

Question 7

State the measures of distress.

Answer 7

*Subjective experience of disease
e.g., pain, discomfort, psychological distress, depressive symptoms

*Sources of information
primarily self-report
for subjects unable to self-report, observational methods may be needed.

Question 8

State the measures of disease.

Answer 8

*Disease definition
Diagnostic criteria
Clinical measures, pathology etc

*Time to key events
Progression to another stage

*Prevalence of disease at specified follow-up time(s)

Question 9

State the measures of diasvility.

Answer 9

*Activities of daily living (ADL)
Independence in basic ADL (e.g., feeding, washing); instrumental ADL (e.g., telephone, money management)

*Sources of information
observation (performance)
self-report
proxy report

Question 10

Define the following measures of death
* Case fatality rate (CFR)
*Five year survival
*Observed survival rate
*Relative survival rate
*Median Survival rate

Answer 10

CFR: Number of people who die from the disease over the number of people having the disease

Five year survival: A proportions of patients who are alive five years after diagnosis over the total number of people who have the disease

Observed survival: An estimate of the probability of surviving

Relative survival rate: ratio of the observed survival rate to the expected survival rate

Median Survival rate: length of time half the study population survives

Question 11

What is lead time bias?

Answer 11

The time between early detection of a disease and the usual clinical diagnosis

Question 12

Explain how the doctor is able to make judgement about when to start or stop treatment and diagnosis?

Answer 12

They evaluate evidence about prognosis for it’s validity, relevance and importance to the patient at hand

Question 13

Describe how a cohort study is done in general

Answer 13

A group of people who do not have a disease and are defined on the basis of different exposures
These people are followed up and the occurrence of a disease is measured in the population over a period of time

Question 14

State the exposure assessments

Answer 14

*Prospective: Measure exposures at onset
Without disease are enrolled and followed overtime to determine the occurrence of a disease

*Retrospective: Exposure is based upon past events
E.g worked in a gas tank factory
Outcomes may be ascertained directly, or also have already occured
Exposure is well defined and occur well before disease

Question 15

Describe the outcome assessments

Answer 15

*Baseline measures: Ensures that the cohort members are free of disease at start
*Outcomes are measured periodically through exams,labs( directly) or through health service utilization and vital statistics ( databases)

• Case definition is very important for outcome assessments

Question 16

State the advantage of cohort studies as prognostic studies

Answer 16

• ideal to study natural history,course of disease and prognostic factors
  *Total population can be studied

Question 17

State the disadvantages of cohort studies as prognostic studies

Answer 17

• etiology research as many exposures cannot be controlled experimentally for ethical reasons

*Intervention not feasible for randomization

*Some outcomes not well measured in trials because they depend more on patients compliance and

*Selection biasis nearly always present, with a high risk of confounding. For example if you compare groups that do and do not smoke, those who smoke may differ in all sorts of other ways from those who do not (for example they may be exposed to higher stress levels, or they may drink more alcohol, or be less likely to exercise, or be less educated, or older).

They are often unsuitable for studying rare conditions. For example setting up a cohort for studying CJD would be doomed to failure even if you restricted it to hamburger eaters (you would probably get no cases); similarly a longitudinal study of all possible nest sites for a bird species would be very unproductive as few if any sites would be utilized. Such studies are better done using case-control designs.

*Exposure status can change over time, but at least you can monitor it in much more detail than with other designs.

*Adequate follow-up can be difficult to sustain, leading to high drop-out rates.

*Retrospective follow-up is only possible if records are available - so this design is mostly used for medical studies.Misclassification biasis a serious threat to validity for retrospective cohort studies

The required duration of the study may be very long, depending on the period of follow up. The sample size also has to be much larger than for other designs, especially for rare conditions. These two features mean that cohort studies can be very expensive to run.

Question 18

Basic principles of good cohort studies

Answer 18

*Good prognostic studies include the confidence intervals in their text, tables, or graphs.

• Confidence interval: Provides the range of values that are likely to include true estimate and quantify the uncertainty in measurement

Question 19

How does the doctor apply about prognosis to the patient?

Answer 19

1. First determine if the patient is so different from those in the study
   You compare demographic information and clinical characteristics)

2.Determine if the evidence will make a clinical importance on your conclusion about what to offer or tell the patient
* Important in deciding whether or not to initiate therapy, monitoring therapy that has already been initiated and for deciding which diagnostic tests to other
* Help with information that may assist in determining what the future is likely to hold