Calculate a confidence interval for a model output by repeatedly replacing the parameters in a fitted model object with a draw from the multivariate normal distribution of the maximum likelihood estimates, then recalculating the output function.

## Arguments

- x
Output from

`flexsurvreg`

or`flexsurvspline`

, representing a fitted survival model object. Or a list of such objects, defining a multi-state model.- B
Number of parameter draws to use

- fn
Function to bootstrap the results of. It must have an argument named

`x`

giving a fitted flexsurv model object. This may return a value with any format, e.g. list, matrix or vector, as long as it can be converted to a numeric vector with`unlist`

. See the example below.- cl
Width of symmetric confidence interval, by default 0.95

- attrs
Any attributes of the value returned from

`fn`

which we want confidence intervals for. These will be unlisted, if possible, and appended to the result vector.- cores
Number of cores to use for parallel processing.

- sample
If

`TRUE`

then the bootstrap sample itself is returned. If`FALSE`

then the quantiles of the sample are returned giving a confidence interval.- ...
Additional arguments to pass to

`fn`

.

## Value

A matrix with two rows, giving the upper and lower confidence limits respectively. Each row is a vector of the same length as the unlisted result of the function corresponding to `fncall`

.

## Examples

```
## How to use bootci.fmsm
## Write a function with one argument called x giving a fitted model,
## and returning some results of the model. The results may be in any form.
tmat <- rbind(c(NA,1,2),c(NA,NA,3),c(NA,NA,NA))
bexp <- flexsurvreg(Surv(Tstart, Tstop, status) ~ trans, data=bosms3, dist="exp")
summfn <- function(x, t){
resp <- flexsurv::pmatrix.fs(x, trans=tmat, t=t)
rest <- flexsurv::totlos.fs(x, trans=tmat, t=t)
list(resp, rest)
}
## Use bootci.fmsm to obtain the confidence interval
## The matrix columns are in the order of the unlisted results of the original
## summfn. You will have to rearrange them into the format that you want.
## If summfn has any extra arguments, in this case \code{t}, make sure they are
## passed through via the ... argument to bootci.fmsm
bootci.fmsm(bexp, B=3, fn=summfn, t=10)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> 2.5% 0.08592861 0 0 0.1375007 0.06010952 0 0.7355608 0.9103557 1
#> 97.5% 0.09767351 0 0 0.1713291 0.08964429 0 0.7652248 0.9398905 1
#> [,10] [,11] [,12] [,13] [,14] [,15] [,16] [,17] [,18]
#> 2.5% 3.724345 0 0 1.965259 3.340625 0 3.920215 6.225585 10
#> 97.5% 3.879065 0 0 2.259760 3.774415 0 4.160991 6.659375 10
bootci.fmsm(bexp, B=3, fn=summfn, t=5)
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9]
#> 2.5% 0.2517227 0 0 0.2579086 0.2297033 0 0.4145488 0.7130623 1
#> 97.5% 0.3156585 0 0 0.2714704 0.2869377 0 0.4902755 0.7702967 1
#> [,10] [,11] [,12] [,13] [,14] [,15] [,16] [,17] [,18]
#> 2.5% 2.711962 0 0 1.049453 2.617790 0 0.9831934 2.144306 5
#> 97.5% 2.967353 0 0 1.101155 2.855694 0 1.1868829 2.382210 5
```