# brokenstick: A package for irregular longitudinal data.

Source:`R/brokenstick-package.R`

`brokenstick-pkg.Rd`

The broken stick model describes a set of individual curves by a linear mixed model using second-order linear B-splines. The main use of the model is to align irregularly observed data to a user-specified grid of break ages.

## Details

The brokenstick package contains functions for fitting a broken stick model to data, for predicting broken stick curves for new data, and for plotting the results.

## Note

This work was supported by the Bill & Melinda Gates Foundation. The contents are the sole responsibility of the authors and may not necessarily represent the official views of the Bill & Melinda Gates Foundation or other agencies that may have supported the primary data studies used in the present study.

## brokenstick functions

The main functions are:

`brokenstick()` | Fit a broken stick model to irregular data |

`plot()` | Plot observed and fitted trajectories by group |

`predict()` | Obtain predictions on new data |

`summary()` | Extract object summaries |

The following functions are user-oriented helpers:

`coef()` | Extract estimated parameters |

`fitted()` | Calculate fitted values |

`get_knots()` | Obtain the knots from a broken stick model |

`get_omega()` | Extract variance-covariance of random effects |

`get_r2()` | Obtain proportion of explained variance |

`model.frame()` | Extract model frame |

`model.matrix()` | Extract design matrix |

`residuals()` | Extract residuals from broken stick model |

The following functions perform calculations:

`set_control()` | Set controls to steer calculations |

`control_kr()` | Set controls for the `kr` method |

## References

van Buuren, S. (2023). Broken Stick Model for Irregular Longitudinal Data.
*Journal of Statistical Software*, 106(7), 1--51.
doi:10.18637/jss.v106.i07

van Buuren, S. (2018). *Flexible Imputation of Missing Data. Second Edition*.
Chapman & Hall/CRC. Chapter 11.
https://stefvanbuuren.name/fimd/sec-rastering.html#sec:brokenstick