# Hazard ratio as a function of time from a parametric survival model

Source:`R/hr_flexsurvreg.R`

`hr_flexsurvreg.Rd`

Hazard ratio as a function of time from a parametric survival model

## Usage

```
hr_flexsurvreg(
x,
newdata = NULL,
t = NULL,
start = 0,
ci = TRUE,
B = 1000,
cl = 0.95,
na.action = na.pass
)
```

## Arguments

- x
Object returned by

`flexsurvreg`

or`flexsurvspline`

.- newdata
A data frame with two rows, each specifying a set of covariate values. The hazard ratio is calculated as hazard(z2)/hazard(z1), where z1 is the first row of

`newdata`

and z2 is the second row.`newdata`

must be supplied unless the model`x`

includes just one covariate. With one covariate, a default is constructed, which defines the hazard ratio between the second and first level of the factor (if the covariate is a factor), or between a value of 1 and a value of 0 (if the covariate is numeric).- t
Times to calculate fitted values for. By default, these are the sorted unique observation (including censoring) times in the data - for left-truncated datasets these are the "stop" times.

- start
Optional left-truncation time or times. The returned survival, hazard or cumulative hazard will be conditioned on survival up to this time. Predicted times returned with

`"rmst"`

,`"mean"`

,`"median"`

or`"quantile"`

will be times since time zero, not times since the`start`

time.A vector of the same length as

`t`

can be supplied to allow different truncation times for each prediction time, though this doesn't make sense in the usual case where this function is used to calculate a predicted trajectory for a single individual. This is why the default`start`

time was changed for version 0.4 of flexsurv - this was previously a vector of the start times observed in the data.- ci
Set to

`FALSE`

to omit confidence intervals.- B
Number of simulations from the normal asymptotic distribution of the estimates used to calculate confidence intervals or standard errors. Decrease for greater speed at the expense of accuracy, or set

`B=0`

to turn off calculation of CIs and SEs.- cl
Width of symmetric confidence intervals, relative to 1.

- na.action
Function determining what should be done with missing values in

`newdata`

. If`na.pass`

(the default) then summaries of`NA`

are produced for missing covariate values. If`na.omit`

, then missing values are dropped, the behaviour of`summary.flexsurvreg`

before`flexsurv`

version 1.2.