Characteristics of included studies not suitable for meta-analysis (non-universal health care systems).

Quality scores range from 1 (lowest quality) to 6 (highest quality).aOdds ratio for increase per $10,000 income.CI, confidence interval; non-UHCS, non-universal health care system; NR, not reported; OR, odds ratio; SEER, National Cancer Institute's Surveillance, Epidemiology and End Results database; SEP, socioeconomic position.