| Study | Country | Date of Data Collection | Sample Sizea | Urban/Rural | Study Design | WTJ/P |
|---|---|---|---|---|---|---|
| Positive Association Between Socioeconomic Status and WTJ/P | ||||||
| Haile M et al. (2014)29 | Ethiopia | 2013 | 845 | Rural | Cross-sectional community based survey | WTJ was 4.2 times higher in richest vs. 2nd poorest quintile (95% CI: 1.6, 10.9) |
| Asfaw A et al. (2004)30 | Ethiopia | 2000, 2001 | 550 | Rural | Cross-sectional community based survey | 1% increase in income increased the WTP by 8.4% |
| Ololo S et al. (2009)31 | Ethiopia | 2007 | 803 | Urban | Cross-sectional community based survey | WTJ was 2.7 times higher in richest vs. poorest quintile. (95% CI: 2.1, 6.7) |
| Zhang L et al. (2006)32 | China | 2002 | 2,830 | Rural | Cross-sectional household survey | WTJ was 1.37–1.66 times higher among farmers who owned luxury assets vs. those who did not |
| Ghosh S et al. (2011)33 | India | NS | 1,502 | Urban | Cross-sectional household survey | WTP was 2.1 times (P=.07) higher in richest vs. poorest quintile |
| Dong H et al. (2005)40 | Burkina Faso | 2001 | 2,414 | NS | Cross-sectional household survey | WTP was 1.7 times higher in richest vs. poorest (P<.01) |
| Onwujekwe O et al.42 | Nigeria | NS | 450 | Both | Cross-sectional household survey | WTP was 1.8 times higher in richest vs. poorest (P=.001) |
| Onwujekwe O et al. (2010)43 | Nigeria | NS | 3,070 | Both | Cross-sectional household survey | WTP was 1.7 times higher in richest vs. poorest quartile |
| Babatunde OA et al. (2012)45 | Nigeria | NS | 360 | Rural | Cross-sectional household survey | WTP was 2 times higher in richest vs. poorest quartile |
| Gustafsson-Wright et al. (2009)46 | Namibia | 2008 | 1,750 | NS | Cross-sectional household survey | WTP was 2.6 times higher in richest vs. poorest quintile; richest willing to pay 1.2% of income while poorest willing to pay 11.4% of income |
| Dror DM et al. (2007)47 | India | NS | 3,024 | Both | Cross-sectional household survey | WTP was 2 times higher in richest vs. poorest |
| Binnendijk B et al. (2013)48 | India | 2008–2010 | 7,874 | Rural | Cross-sectional household survey | Richest willing to pay more than poorest but poorest willing to pay higher proportion of total income |
| Shafie AA et al. (2013)49 | Malaysia | 2009 | 472 | NS | Cross-sectional household survey | WTP was 2 times higher in richest vs. poorest quintile |
| Parmar D et al. (2014)51 | Burkina Faso | 2004–2008 | 6,827 | Both | Cross-sectional household survey | WTJ was 0.27 lower in poor vs. rich (P=.001) |
| Negative Association Between Socioeconomic Status and WTJ/P | ||||||
| Oriakhi HO et al. (2012)36 | Nigeria | NS | 360 | Rural | Cross-sectional household survey | WTJ was 0.66 times lower in high- vs. low-income groups |
| Mixed Results or No Association | ||||||
| Bukola A (2013)35 | Nigeria | NS | 900 | Both | Cross-sectional household survey | 53% decrease in WTP with 1 unit increase in income quintile in rural areas; conversely, 77% increase in WTP with 1 unit increase in income quintile in urban areas |
| Eckhardt M et al. (2011)36 | Ecuador | 2006 | 153 | Rural | Cross-sectional household survey | No difference in WTJ by income groups (P=.23) |
Abbreviations: CI, confidence interval; NS, not stated in article; WTJ, willingness to join; WTP, willingness to pay.
↵a Sample size is the number of households.