Mixed-Effects Tobit Joint Models for Longitudinal Data with Skewness, Detection Limits, and Measurement Errors

Figure 1

The histograms (a,b) of viral load measured from RNA levels (in natural ln scale) and standardized CD4 cell count in plasma for 44 patients in an AIDS clinical trial study. Profiles (c,d) of viral load (response) in ln scale and CD4 cell count (covariate) for three randomly selected patients. The vertical and horizontal lines in (a) and (c) are below the detectable level of viral load (3.91=ln(50)).

(a) Histogram of viral load in ln scale

(b) Profiles of viral load in ln scale

(c) Profiles of CD4 cell count

(d) Histogram of CD4 cell count