# Ch. 6 Natural History of Disease: Ways of Expressing Prognosis Flashcards

Why is the characterization of the natural history of disease in qualitative terms important?

1) Necessary to describe the severity of the disease and establish services and public health programs.

2) To answer questions regarding prognosis

3) Important to establish baseline in the natural history of the disease, so that as new treatments become available the effects can compared with the expected outcome without them.

How can we describe the prognosis in therms of the schematic on (figure 6.) - a straight-line ?

(Point A) describes the biological onset of the disease.Though it usually cannot be determined as it occurs sub-clinically.

(Point P) Pathogenic evidence that disease is be carried if sought be the patient.

(Point S) Signs and symptoms of the disease develop.

(Point M) Medical attention is sought out by the patient.

(Point D) Medical Diagnosis is made by a medical professional

(Point T) Treatment of the is given. Which can result in cure, management ( with/without disability), and even death.

When do most typically medical and scientific journals calculate survival time of the patient?

Ideally we would like to begin at the biological onset of disease, but mostly impossible. In order to standardize the calculations the Duration of survival is counted from the time of diagnosis; though because patients may differ at the point in which they seek out medical attention the survival time may vary.

True or False: When Determining Prognosis. An important related question is “How is the Diagnosis made?” Such a test is often not available and thus can lead to variability in the interpretation of the results.

True.

Explain How Prognosis can be expressed.

Prognosis can be expressed in terms of death from the disease or terms of survivorship of the disease, with the endpoints being death, intervals of diagnosis to recurrence, diagnosis to functional impairment, disability, or changes in the patients quality of life;which can be affected by the treatment or alleviation of symptoms caused by the disease despite the extension of their life.

How do we calculate the case-fatality rate as it can be used as the first way to express prognosis?

Case-Fatality = # of people who have died from the disease / #of people who have the disease

When is the case facility an ideal measure of the prognosis of the disease?

Case fatality does not use an implicit measure of time as it is used for acute diseases in which the outcome of death occurs soon after diagnosis. Thus, in chronic diseases it becomes a less useful measure.

Describe Person-Years as a useful way of expressing mortality?

Person-Years = # of deaths per year/ Person years the group was observed

*One problem in using operon years is that each person-year is assumed to be equivalent to every other person-year (i.e. the risk is the same).

What is the Five-Year Survival rate? (expressing prognosis)

Five Year Survival rate- is the percentage of patients who are alive 5 years after treatment begins or 5 years after being diagnosed with the disease.

What problem are we seeing now with the use of the Five-Year survival rate?

1) The problem we are now seeing with the Five -Year survival rate has been the increase of screening programs thus leading to artifacts through earlier diagnosis.

2) We cannot look at a criterion for a group of patients who were diagnosed less than 5 years ago or a therapy that was introduced less than 5 years ago.

3) Though the 5 year survival rate may be identical in different populations or diseases it is unclear as to which years the actual rate of deaths occurred during those years.

What is Lead time?

Lead Time- the interval between earlier diagnosis made possible by screening and the later usual time of diagnosis.

What is the Life Table? Another approach for prognosis.

For each calendar year of treatment, the table shows the # of patients enrolled in treatment and the # of patients at each calendar year after the initiation of treatment. As the data shows the # patients who are alive each calendar year and at the anniversary of initiation of treatment.

How do we calculate the percent of survival after the 1st yr of treatment in a life table? After obtaining the data for 5 years how do we calculate the survival?

Thus to answer what percent survived after 1 yr., we divide the total # of patients who were alive 1 yr. after the initiation of treatment by the total # of patients who started the treatment or after each year. To calculate the probability of surviving 5 years we multiply the percentage obtained for all 5 years.

True or False. Withdrawals (loses to follow-up) can be found and thus continue to participate within the study.

False. Withdrawals (loses to follow-up) cannot be found or decline and thus refuse to continue to participate within the study.

How do you set up a Life Table using Columns?

Column 1) The interval since the beginning of treatment

Column 2) # of individuals alive at the beginning of treatment

Column 3) #of people who died during the interval

Column 4) #of individuals who withdrew from the study

Column 5) # of individuals who are effectively at risk of dying during the interval ( calculated as column 2 - 1/2 column 4)

Column 6) The proportion who died during the interval (col.3/col.5)

Column 7) The proportion of who did not die during the interval (1 - col.6)

Column 8) The proportion who survived from the point at which they were enrolled in the study to the end of the interval (col. 7 X col.8)