Agricultural price transmission across space and time: The case of cowpea and yam markets in Nigeria
The transmission of price changes to markets has attracted renewed interest since the international food price spikes of 2007 to 2011. In response to this, this paper investigates the long-run behaviour of Nigerian cowpeas and yam tuber retail prices across space and time from 2000 to 2015. We employed the augmented Dickey-Fuller unit root test, the Johansen co-integration test, the Granger causality test, the vector error-correction model (VECM) and variance decomposition analysis. The Johansen co-integration test confirmed the presence of a long-run relationship across the markets, while the VECM revealed that the speed of adjustment to equilibrium after price shocks in the yam and cowpea markets varied across space (market) and period (time), with the food crisis in the period pre-2007 to 2011 fastest and the food crisis in the period 2007 to 2011 slowest. We are of the opinion that the presence of a long-run relationship in Nigerian cowpea and yam markets is a call for participants to explore opportunities for gainful trade.