Calculation of median, Q1, and Q3 with survival probabilities in Nonparametric Distribution Analysis (Right-Censoring)

You can use survival probabilities in nonparametric distribution analysis (right censoring) with the Kaplan-Meier estimates to calculate the median, the first quartile (Q1), and the third quartile (Q3):
  • The median is the time associated with the first survival probability in the table less than or equal to 0.50.
  • Q1 is the time associated with the first survival probability in the table less than or equal to 0.75.
  • Q3 is the time associated with the first survival probability in the table less than or equal to 0.25.
For example, suppose you have the following output:

Distribution Analysis: Temp100

Variable: Temp100

Censoring Censoring Information Count Uncensored value 34 Right censored value 6 Censoring value: Cens100 = 0

Nonparametric Estimates

Characteristics of Variable Standard 95.0% Normal CI Mean(MTTF) Error Lower Upper Q1 Median Q3 IQR 44.7813 4.43366 36.0914 53.4711 24 38 54 30
Median = 38
The first survival probability in the table that is less than or equal to 0.50 is 0.475. The time associated with this survival probability is 38; therefore, the median is 38.
Q1 = 24
The first survival probability in the table that is less than or equal to 0.75 is 0.75. The time associated with this survival probability is 24; therefore, Q1 is 24.
Q3 = 54
The first survival probability in the table that is less than or equal to 0.25 is 0.25. The time associated with this survival probability is 54; therefore, Q3 is 54.

If the survival probability cannot be found in the table, then the quartile or median value is displayed as an *. For example, in the following table, there is no survival probability less than or equal to 0.25, so Q3 is *.

Distribution Analysis: Temp80

Variable: Temp80

Censoring Censoring Information Count Uncensored value 37 Right censored value 13 Censoring value: Cens80 = 0

Nonparametric Estimates

Characteristics of Variable Standard 95.0% Normal CI Mean(MTTF) Error Lower Upper Q1 Median Q3 IQR 63.7123 3.83453 56.1968 71.2279 48 55 * *
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