apv_se function

Bootstrap standard errors for SITAR peak velocity and age at peak velocity

apv_se bootstraps a SITAR model to generate standard errors for age at peak velocity (apv) and peak velocity (pv).

apv_se(object, fun = getPeak, nboot = 10, seed = NULL, plot = FALSE, ...)

Arguments

• object: SITAR model.

• fun: function to extract apv and pv from velocity curve (default getPeak), alternative getTakeoff or getTrough.

• nboot: number of bootstrap samples (default 10).

• seed: integer to initialize the random number generator (default NULL).

• plot: logical to control plotting (default FALSE).

• ...: optional arguments defining the velocity curve to be bootstrapped (plot.sitar arguments xfun, yfun, subset, ns

  or abc), and graphical par parameters.

Returns

a 2x2 array giving the mean and standard error of apv and pv, with attribute "bs" a tibble containing the bootstrap estimates of apv and pv, with NAs removed.

Details

If plot is TRUE, the original velocity curve is plotted along with each bootstrap sample's pv versus apv.

Examples

data(heights)
## fit sitar model for height
model <- sitar(x = age, y = height, id = id, data = heights, df = 4)

## bootstrap standard errors for age at peak velocity and peak velocity
output <- apv_se(model, nboot=3, seed=111, plot=TRUE)

Author(s)

Tim Cole tim.cole@ucl.ac.uk