Joshua’s research is in the field of Demography, Demographic Economics, and Development Economics, with an emphasis on the causes and economic effects of fertility change. His focus is on four major research areas:  1) macroeconomics effects of fertility decline in low- and middle-income countries, 2) climate change and fertility, 3) health shocks (primarily COVID-19 and malaria) on fertility and prenatal mortality, and 4) gender discrimination on birth and economic outcomes.

He is the co-creator of the Canning-Karra-Wilde (CKW) model, one of the leading tools used to calculate the Demographic Dividend. He has published in leading journals in both the fields of economics and demography, such as the American Economic Review, the European Economic Review, Demography, and the Population and Development Review. He is currently one of two Editors of the Population and Development Review.  He also co-chairs the IUSSP Panel on Covid-19, Fertility, and the Family. 

He recently brought a £1.7 million UKRI Frontier Research Grant (converted from an ERC Consolidator Award) to LCDS at the University of Oxford to study the determinants of natural sex ratios at birth through the SEXRATIO project. He is jointly a Research Scientist at the Population Research Center at Portland State University, and a Research Fellow at the IZA Institute for Labor Economics. Before joining LCDS, he was the Deputy Head of the Laboratory of Fertility and Well-Being at the Max Planck Institute for Demographic Research, and an assistant professor of Economics at the University of South Florida.  He regularly consults for leading international organizations, such as the World Bank and the United Nations.