TABLE 3—

Reviews That Considered the Health Impacts of Income Inequality

Author	Critical Appraisala	Review Quality Summaryb	Included Study Quality	Context	Summary of Insights
Kondo et al.76	2–4, 6, 7,c 8,c 9–11	Moderate	Unclear	Mostly high-income countries, but some Latin American and Eastern European countries and China	There was an adverse effect of income inequality on health, especially when the Gini was > 30 and after 1990 and where time lags were accounted for.
Kondo et al.77	2–4, 6, 7,c 8,c 9–11	Moderate	Unclear	Mostly high-income countries, but some Latin American and Eastern European countries and China	The health–income inequality relationship was stronger with larger population units (for SRH), and lag, threshold, and period effects all remained important explanatory factors after adjusting for area size.
Adjaye-Gbewonyo and Kawachi78	2,c 4, 5, 9, 10, 11c	Low	Not reported	United States, Great Britain, China, Japan, Australia, and South Africa	Greater relative deprivation was associated with higher mental ill health, higher mortality, and lower SRH.
Furnee and Pfann79	2,c 5, 9c	Low	Not reported	Europe (mostly northern Europe) and United States	Self-rated health at lower income levels was worse in more unequal countries.
Judge et al.80	4,c 9,c 10, 11c	Low	Not reported	Large range of countries included in panel data, including low- and middle-income nations	Greater income inequality in high-income countries was associated with higher mortality and lower life expectancy but the sample and measures were limited.
Lynch et al.39	9,c 10, 11c	Low	Not reported	Wide range of countries, but most were high-income	There was little evidence that income inequality is a major generalizable determinant of population health difference within or between rich countries, but there was stronger evidence that greater poverty is.
Macinkoet al.81	2, 4,c 9,c 10, 11c	Low	Not reported	Not clear	The relationship between income inequality and health was unclear.
Pickett and Wilkinson82	10	Low	Not reported	High-income countries	There was sufficient evidence to conclude that income inequality causes lower life expectancy in high-income countries.
Spencer83	4, 7,c 8,c 9, 10, 11c	Low	Unclear	Mostly Europe and North America, with some studies of Australia and Japan	Greater income inequality and less redistribution were associated with higher infant mortality rates in high-income countries.
Wilkinson and Pickett84	7,c 8,c 9,c 10, 11c	Low	Not reported	Wide range of countries, but mostly high-income	There were more studies than not showing a strong association between income inequality and mortality when large population units were compared and where potential mediators were not adjusted for.
Rowlingson85	10, 11	Low	Not reported	Not clear	There was evidence of a link between income inequality and worse health.
Kim56	2, 4, 9–11	Low	Not reported	Higher-income countries, especially Nordic countries	In high-income counties, income inequality was associated with worse infant and child mortality, but not at other ages. The Scandinavian welfare regime was associated with better infant and child mortality but not at other ages.
Lago et al.86	2,c 9–11	Low	Not reported	Not clear	Income inequality was associated with greater health inequality across the population and worse population health.

Note. SRH = self-rated health.

^aCritical appraisal criteria: 1 = an a priori design for the review was provided; 2 = a comprehensive search was undertaken (including relevant search terms and at least 2 databases); 3 = studies were selected for inclusion by at least 2 independent researchers; 4 = there were clear inclusion and exclusion criteria; 5 = the status of publication (e.g., gray literature) was ignored in the inclusion and exclusion criteria; 6 = the data were extracted independently by at least 2 researchers; 7 = the scientific quality of the included studies was assessed and documented; 8 = the scientific quality of the included studies was used appropriately in formulating conclusions; 9 = the methods used to combine the findings of studies was appropriate; 10 = the likelihood of publication bias was assessed (if possible); 11 = there were no important conflicts of interest that may have had an impact on the conclusions.

^bQuality assessment: all (very high); at least 2, 4, 7, 8, 9 (high); at least partially 2, 4, 7, 8, 9 (moderate); all others (low).

^cDenotes a partially fulfilled criterion.