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Right censoring occurs when the exact survival time becomes incomplete at the
right side of the follow-up period. For example, if a patient is still alive at the end
of a study. Left censoring occurs when the survival time becomes incomplete at
the left side of the follow-up period. For instance, when the event of interest occurs
before this particular observation enters a study and the exact time is unknown.
Independent censoring, also called noninformative censoring, means the censor-
ing is independent with the event of interest. For example, administrative censoring
is one kind of independent censoring, e.g. a subject has not yet had an event due to
the administrative termination of a study. By contrast, dependent censoring, also
called informative censoring, means the censoring is dependent on the event.
If there is more than one risk that can trigger the event of interest, we call those
risks competing risks. When one risk happens, it will prevent the other risk from
happening.
2.3.2 Basic functions and curves
In order to model the time until the event occurs, several basic functions are intro-
duced:
1. Probability density function (pdf),
ж = (2-5)
A probability density function indicates the instantaneous death rate at time t.