param_current: A numeric vector of regression parameters, in the order β,γ. The γ vector is obtained from the matrix form. In matrix form, the gamma parameter matrix rows correspond to parameters for the Y* = 1
observed outcome, with the dimensions of Z. In matrix form, the gamma parameter matrix columns correspond to the true outcome categories j=1,…,n_cat. The numeric vector gamma_v is obtained by concatenating the gamma matrix, i.e. gamma_v <- c(gamma_matrix).
obs_Y_matrix: A numeric matrix of indicator variables (0, 1) for the observed outcome Y*. Rows of the matrix correspond to each subject. Columns of the matrix correspond to each observed outcome category. Each row should contain exactly one 0 entry and exactly one 1 entry.
X: A numeric design matrix for the true outcome mechanism.
Z: A numeric design matrix for the observation mechanism.
sample_size: An integer value specifying the number of observations in the sample. This value should be equal to the number of rows of the design matrix, X or Z.
n_cat: The number of categorical values that the true outcome, Y, and the observed outcome, Y* can take.
Returns
COMBO_EM_function returns a numeric vector of updated parameter estimates from one iteration of the EM-algorithm.