This study attempts to address the issues of "reliability" and "robustness" in the supply parameters using pooled time series data for wetland rice in Java. In particular, the sensitivity of the yield and input demand elasticities are evaluated due to differences in specification of farmers' expectations variables, alternative data sources, (dis)aggregation of inputs, and functional forms. The analysis indicates that the yield and fertilizer input elasticities are fairly robust across different specifications. However, the estimates of labor demand elasticities are quite sensitive to data and model specifications.