Median Rank for Multiple Censored Data

This example compares the median rank calculation for multiple censored data.

Table 3.1 on page 78 in book “Reliability & Life Testing Handbook Vol 2” by Dr. Kececioglu, Prentice-Hall, 1994.

The coordinates of each point in the following plot shows the failure time and the corresponding median rank.



The differences between the results in Weibull++ and the book are due to the method of calculating the median ranks (MR). In the book, the following approximation method is used.


 * $$MR_{i}\approx \frac{MON_{i}-0.3}{N+0.4}$$

where $$MR_{i}\,\!$$ is the median rank at the $$ith\,\!$$ failure time; $$MON_{i}\,\!$$ is the mean order number; $$N\,\!$$ is the total samples. For the step by step calculation of mean order number (MON), please refer to the book “Reliability & Life Testing Handbook Vol 2” by Dr. Kececioglu, Prentice-Hall, 1994.

In Weibull++, the following exact method is used.


 * $$MR_{i}= \frac{1}{1+\frac{N-MON_{i}+1}{MON_{i}}F_{0.5,m,n}}$$

where $$m=2(N-MON_{i}+1), n=2xMON_{i}\cdot F_{0.5,m,n}\,\!$$ is the 50 percentile of a F distribution with degree of freedom of m and n.