Two authors (CMW and LW) independently reviewed studies for compliance with the selection criteria. Papers that passed the screening of title and abstract underwent full article review. The reference lists of the articles selected for final inclusion were also checked along with directly relevant review articles identified. The authors independently extracted study data including: 1) study objective(s); 2) study setting; 3) study design and population size; 4) incentives provided to supervisors; 5) inclusion and exclusion criteria for different DOT strategies; 6) comparator group(s); 7) study outcomes & results; 8) study limitations; 9) main conclusion(s) and 10) study funding source(s). Disagreements in article selection and data extraction were settled through discussion.