Figure 2. Pooled Overall Survival by Quality Adjustment Scores.

All studies are listed in the References list at the end of this article. Quality was assessed on a 16-point scale with higher scores indicating less potential for confounding or bias. Studies were classified as low-quality (≤6 points), medium-quality (7 points), and high-quality (≥8 points). See eTable 5 in Supplement 1 for factors used in scoring and eTable 9 in Supplement 1 for quality scores of individual studies. Some studies had multiple comparisons and, to differentiate them, superscript letters are noted by each comparison. The distinctions can be found in eTable 8 in Supplement 1.