HAZARD

HAZARD (LET)

Let Subcommand

Compute the hazard for a set of failure times.

The hazard is constructed as follows:
1. Sort and rank the N failure times from shortest to longest failure time. Note that the hazard can accomodate data where the time may be a censoring time rather than a failure time (i.e., the unit was taken out of service before it failed).

2. Calculate a hazard value at each of the failure times. Note that the hazard is only caclulated at failure times, not censoring times. The hazard is:
   100.0*(1/(N-K+1)

   where K is the rank of the failure time. This expresses the hazard as a percentage. You can express the hazard as a proportion by omitting the multiplication by 100.

LET <y> = HAZARD <x> <tag>             <SUBSET/EXCEPT/FOR qualification>
where <x> is the variable containing the failure times;
            <tag> is a variable that indicates whether the corresponding element of <x> is a failure time or a censoring time;
            <y> is a variable where the hazards are saved;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

A value of 0 for <tag> is used to signify a censoring time and a value of 1 for <tag> is used to signify a failure time. Dataplot uses 0.5 as the cutoff. That is, any value greater than or equal to 0.5 is interpreted as a failure time.

LET Y = HAZARD X CENSOR
LET Y = HAZARD X CENSOR SUBSET CENSOR = 1

Hazards are only computed for failure times (i.e., where = 1), not censoring times. The saved hazards () are set to 0 for censoring times. If you just want to keep the hazards at failure times, do something like:
LET Y = HAZARD X CENSOR
RETAIN Y SUBSET CENSOR = 1


The censoring times do affect the value of the hazard since they are used in determining the rank. If you only want the failure times to be used in the calculation of the hazard, do something like the following:

LET Y = HAZARD X CENSOR SUBSET CENSOR = 1
RETAIN Y SUBSET CENSOR = 1

None

None

CUMULATIVE HAZARD	= Compute the cumulative hazard for a variable.
HAZARD PLOT	= Generate a hazard plot.
PROBABILITY PLOT	= Generate a probability plot.
WEIBULL PLOT	= Generate a Weibull plot.
INTERARRIVAL TIME	= Compute the interarrival times of a variable.

Reliability

1998/5

SKIP 25
READ HAHN.DAT Y TAG
LET TAG = 0 SUBSET TAG = 2
LET Z = HAZARD Y TAG