"The gap between richer (high- and upper-middle-income) and poorer (lower-middle- and low-income) countries remained largely unchanged over time."
www.healthaffairs.org/doi/epdf/10....
"The gap between richer (high- and upper-middle-income) and poorer (lower-middle- and low-income) countries remained largely unchanged over time."
www.healthaffairs.org/doi/epdf/10....