getMIX_UNI.addpara function

Get Additional Parameters Related to Interval-specific Slopes, Interval-specific Changes and Values of Change-from- baseline for a Mixture Model or Multiple Group Model with Latent Change Score Models for Longitudinal Outcome

This function derives additional parameters for a mixture model with latent change score models as submodels. In particular, it specifies the means and variances of interval-specific slopes, interval-specific changes, and values of change-from-baseline.

getMIX_UNI.addpara(
  dat,
  nClass,
  curveFun,
  intrinsic,
  t_var,
  records,
  growth_TIC,
  decompose,
  starts
)

Arguments

• dat: A wide-format data frame, with each row corresponding to a unique ID. It contains the observed variables with repeated measurements and occasions for each longitudinal process, and time-invariant covariates (TICs) if any. It takes the value passed from getMIX() or getMGroup().

• nClass: An integer specifying the number of classes for the mixture model or multiple group model. It takes the value passed from getMIX() or getMGroup().

• curveFun: A string specifying the functional form of the growth curve. Supported options for latent change score models include: "quadratic" (or "QUAD"), "negative exponential" (or "EXP"), "Jenss-Bayley"

  (or "JB"), and "nonparametric" (or "NonP"). It takes the value passed from getMIX() or getMGroup().

• intrinsic: A logical flag indicating whether to build an intrinsically nonlinear longitudinal model. It takes the value passed from getMIX() or getMGroup().

• t_var: A string specifying the prefix of the column names corresponding to the time variable at each study wave. It takes the value passed from getMIX() or getMGroup().

• records: A numeric vector specifying indices of the study waves. It takes the value passed from getMIX()

  or getMGroup().

• growth_TIC: A string or character vector specifying the column name(s) of time-invariant covariate(s) contributing to the variability of growth factors if any. It takes the value passed from getMIX() or getMGroup().

• decompose: An integer specifying the decomposition option for temporal states. Supported values include 0 (no decomposition), 1 (decomposition with interval-specific slopes as temporal states), 2 (decomposition with interval-specific changes as temporal states), and 3 (decomposition with change-from-baseline as temporal states). It takes the value passed from getTVCmodel(). It takes the value passed from getMIX() or getMGroup(). The argument is set as NULL when the submodel is a latent change score model.

• starts: A list of initial values for the parameters, either takes the value passed from getMIX() or getMGroup(), or derived by the helper function getMIX.initial() or getMGroup.initial().

Returns

A list containing the specification of the means and variances of interval-specific slopes, interval- specific changes, and values of change-from-baseline for latent change score models.