The window with settings for
life tables is accessed via the menu
Life tables are created for time ranges with equal spans, provided by the researcher. The ranges can be defined by giving the step. For each range PQStat calculates:
standard error of the survival function;
standard error of the probability density;
standard error of the hazard rate
In the case of a lack of complete observations in any range of survival time range there is the possibility of using correction. The zero number of complete cases is then replaced with value 0.5.
We can illustrate the information obtained thanks to the life tables with the use of several charts:
Patients' survival rate after the transplantation of a liver was studied. 89 patients were observed over 21 years. The age of a patient at the time of the transplantation was in the range of yearsyears. A fragment of the collected data is presented in the table below:
The complete data in the analysis are those as to which we have complete information about the length of life after the transplantation, i.e. described as „death” (it concerns 53 people which constitutes 59.55% of sample). The censored data are those about which we do not have that information because at the time when the study was finished the patients were alive (36 people, i.e. 40.45% of them). We build the life tables of those patients by creating time periods of 3 years:
For each 3-year period of time we can interpret the results obtained in the table, for example, for people living for at least 9 years after the transplantation who are included in the range [9;12): \item the number of people who survived 9 years after the transplantation is 39, \item there are 7 people about whom we know they had lived at least 9-12 years at the moment the information about them was gathered but we do not know if they lived longer as they were left out of the study after that time, \item the number of people at the risk of death in that age range is 36, \item there are 14 people about whom we know they died 9 to 12 years after the transplantation, \item 39.4% of the endangered patients died 9 to 12 years after the transplantation, \item 60.6% of the endangered patients lived 9 to 12 years after the transplantation, \item the percent of survivors 9 years after the transplantation is 61.4% 5%, \item 0,08 0.02 is the death probability for each year from the 9-12 range. The results will be presented on a few graphs:
The probability of survival decreases with the time passed since the transplantation. We do not, however, observe a sudden plunge of the survival function, i.e. a period of time in which the probability of death would rise dramatically.