Chapter 6 Notes

Natural History of Disease: Ways of Expressing Prognosis

1.) Case-fatality rate: Number of people who die of a diesease/ Number of people who have the disease
- This is good at estimating an individual's chance of dying from a disease, if the disease resolves or kills quickly. (ex: smallpox=short-term)

2.) Person-Years: Number of deaths/ person-years over which a group is observed
ex: Childhood death rates: Childhood disease disproportinatley kill 0-2yr. old
10 kids and they followed from birth-5yrs. or had 25 kids and followed them from birth-2yrs.
-Different data if looking at: What's the risk/person-year of dying of SIDS?
-The first study of 10 kids in which they followed for 5yrs does not help in answering this question because of the nature of the diseaese in this case. SIDS occurs in the first two years of life, in which the second study would be better. An example of a disease that would be good for the first study would be Leukemia because the older a child gets, the more likely they are to develop leukemia.
-The study design used is dependent on what you know about the biology of the disease being studied.

3.) 5-Year Survival Rate: The percentage of patients who are alive at 5yrs after treatment begins or 5yrs after diagnosis. This study design is used when there is not a lot known about the course of the disease. It is really good to use with deaths from cancer.
Problems: ex: Cancer that afflicts ment over 70 (Non-AIDS Kaposi's Sarcoma) They do not expect him to live whether this cancer is really killing him or not.
ex: Chilhood Leukemia vs. Non-AIDS Kaposi's Sarcoma
-All patients young -Elderly patients
-5yr survival rate is likely -5years is not expected survival
if a patient was disease-
free

4.) Lead-Time: Time between diagnosis and symptoms or the time between diagnosis and death. (If you improve diagnostic techniques, then you will catch more cases of the disease earlier (= an increase in lead time)

5.) Life Table Analysis: Actual observed survival over time. (ex: prognosis: patent has a certain amount of years left to live and in x amount of time the patient will probably be dead. Pg: 119: Table 6-2 and 6-3
Probability of Surviving : Total # of patients who were alive 1yr. after initiation of treatment/ Total # of patients who started treatment
-For thos that made it throught the 1st year, What's the probability for these people making it through the second year?

  1. of ppl alive at end of 2nd yr. / Total Number of patients alive after yr. 1 (Those who do not qualify )

-This trend continues for each year.
Product of probabilities of survival per year= Combined probability of surviving all 5 years.

- More precise understanding on mortality of disease with more people and less time, since the majority of people die within the first few years.

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