msm: crudeinits.msm – R documentation

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crudeinits.msm

Calculate crude initial values for transition intensities

Description

Calculates crude initial values for transition intensities by assuming that the data represent the exact transition times of the Markov process.

Usage

crudeinits.msm(formula, subject, qmatrix, data=NULL, censor=NULL, censor.states=NULL)

Arguments

`formula`	A formula giving the vectors containing the observed states and the corresponding observation times. For example, `state ~ time` Observed states should be in the set `1, ..., n`, where `n` is the number of states. Note hidden Markov models are not supported by this function.
`subject`	Vector of subject identification numbers for the data specified by `formula`. If missing, then all observations are assumed to be on the same subject. These must be sorted so that all observations on the same subject are adjacent.
`qmatrix`	Matrix of indicators for the allowed transitions. An initial value will be estimated for each value of qmatrix that is greater than zero. Transitions are taken as disallowed for each entry of `qmatrix` that is 0.
`data`	An optional data frame in which the variables represented by `subject` and `state` can be found.
`censor`	A state, or vector of states, which indicates censoring. See `msm`.
`censor.states`	Specifies the underlying states which censored observations can represent. See `msm`.

Details

Suppose we want a crude estimate of the transition intensity q_rs from state r to state s. If we observe n_rs transitions from state r to state s, and a total of n_r transitions from state r, then q_rs / q_rr can be estimated by n_rs / n_r. Then, given a total of T_r years spent in state r, the mean sojourn time 1 / q_rr can be estimated as T_r / n_r. Thus, n_rs / T_r is a crude estimate of q_rs.

If the data do represent the exact transition times of the Markov process, then these are the exact maximum likelihood estimates.

Observed transitions which are incompatible with the given qmatrix are ignored. Censored states are ignored.

Value

The estimated transition intensity matrix. This can be used as the qmatrix argument to msm.

Author(s)

C. H. Jackson chris.jackson@mrc-bsu.cam.ac.uk

Examples

data(cav)
twoway4.q <- rbind(c(-0.5, 0.25, 0, 0.25), c(0.166, -0.498, 0.166, 0.166),
c(0, 0.25, -0.5, 0.25), c(0, 0, 0, 0))
statetable.msm(state, PTNUM, data=cav)
crudeinits.msm(state ~ years, PTNUM, data=cav, qmatrix=twoway4.q)

msm

Multi-State Markov and Hidden Markov Models in Continuous Time

v1.6.8

GPL (>= 2)

Authors

Christopher Jackson <chris.jackson@mrc-bsu.cam.ac.uk>

Initial release

2019-12-16