The Relationship between the Physical Quality of Rice and the Market Price: A Case Study in Savannakhet, Laos, Using a Bayesian Approach

The visual characteristics of rice grains play a primary role in determining the market price, and are used for grading systems in many rice-consuming countries. Laos is a rice-consuming country in Southeast Asia, but it does not have a functioning grading system. This study investigated the relationship between the physical quality of milled rice grains and the market price based on the Bayesian approach in Savannakhet, Laos. We collected 30 rice samples and their market prices from 12 shops, including imported rice from Thailand and Vietnam. The rice samples were scanned using a Grain Scanner, and the proportion of head rice (HR, %) was determined using physical traits (length, shape, color, etc.) based on the 'Thai standard' grading criteria. The relationship between the HR ratios and market prices was modeled with the Bayesian approach. For Laos's product, the market price and HR ratio were lower than those for Thailand's product. Based on the Bayesian framework, the results of Markov Chain Monte Carlo simulations indicated that (1) the market price of Thailand's product was mostly determined by the HR ratio, but other factors, such as aroma, were also suggested, especially in high-quality rice grains; (2) Laos's product showed a positive correlation, but other factors had a greater influence on Laos's product than Thailand's product; and (3) no clear relationship was found in Vietnam's product due to the limitation of a small number of samples, which was also considered a difference in consumer needs. These results indicated that the relationship between rice quality and market price for Laos's product was unstable compared to that for Thailand's product. To promote a more market-oriented agricultural sector, this pilot study has been broadened to examine other factors and extended to other cities or regions in Laos.