getMED.initial function

Compute Initial Values for Parameters of Longitudinal Mediation Models

This function computes the initial values of the parameters for a longitudinal mediation model.

getMED.initial(
  dat,
  t_var,
  y_var,
  m_var,
  x_type,
  x_var,
  curveFun,
  records,
  res_scale,
  res_cor
)

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 multiple longitudinal processes and a baseline predictor when applicable. It takes the value passed from getMediation().

• t_var: A vector of strings, with each element representing the prefix for column names related to the time variable for the corresponding longitudinal variable at each study wave. It takes the value passed from getMediation().

• y_var: A string specifying the prefix of the column names corresponding to the outcome variable at each study wave. It takes the value passed from getMediation().

• m_var: A string specifying the prefix of the column names corresponding to the mediator variable at each study wave. It takes the value passed from getMediation().

• x_type: A string indicating the type of predictor variable used in the model. Supported values are "baseline"

  and "longitudinal". It takes the value passed from getMediation().

• x_var: A string specifying the baseline predictor if x_type = "baseline", or the prefix of the column names corresponding to the predictor variable at each study wave if x_type = "longitudinal". It takes the value passed from getMediation().

• curveFun: A string specifying the functional form of the growth curve. Supported options include: "linear"

  (or "LIN"), and "bilinear spline" (or "BLS"). It takes the value passed from getMediation().

• records: A list of numeric vectors, with each vector specifying the indices of the observed study waves for the corresponding longitudinal variable. It takes the value passed from getMediation().

• res_scale: A numeric vector with each element representing the scaling factor for the initial calculation of the residual variance. These values should be between 0 and 1, exclusive. It takes the value passed from getMediation().

• res_cor: A numeric value or vector for user-specified residual correlation between any two longitudinal processes to calculate the corresponding initial value. It takes the value passed from getMediation().

Returns

A list containing the initial values for parameters related to growth factors and path coefficients of a longitudinal mediation model.