CHAPTER 6 :Ways of Expressing Prognosis

person years

Apparent effects on prognosis of improvement in Diagnosis

GENERALIZABILITY OF SURVIVAL DATA

characterize the natural history of disese in quantitative terms

  1. describe the severity of a disease to establish priorrities for clinical service and public health program
  1. patien often ask question about prognosis
  1. quantification is important to establish a baseline for natural history so that as new treatmen become availabe the effect of these treatments can be compare with the expected outocome

is term of the number of deaths divided by the person years over which a group is observed

person years are useful as denominators of rates of event in many situations such as randomized trial & cohort studies

5 APPROACH TO EXPRESSING PROGNOSIS

1 . Case fatality rate

ideally suited to disease : short-term and acute condition

Denominator = number of people who have the disease

is defined as the number of people who die of a disease divided by the number of people who have the disease

  1. Five Year Survival

Lead time : gap time during early screening time to general time of diagnosis

2 limitation : no temporary change over the period ,lost off follow up, experience with 5 years

Definition : is the percentage of patients who are alive 5 years after treatment begins or 5 years after diagnosis

Application: frequently used in clinical medicine ex: cancer

  1. OBSERVED SURVIVAL rate

2 APPROACH FOR CALCULATION OBSERVED SURVIVAL OVER TIME

Calculating a Life Table

in 5 years we loss bit chance of data in 5 years , who can follow just 2 or 3 years, so subject who not complete the 5 years still can be come to the calculation data

withdrawals : person for whom data are not available for the full period of follow up either because follow up was not possible or because they were enrolled after the study was stared

Rationale for the Life Table

the use of data is economical and efficient

  1. MEDIAN SURVIVAL TIME
  1. RELATIVE SURVIVAL

THE KAPLAN MEIER METHOD

ASSUMTIONS MADE IN USING LIFE TABLE