摘要：One potentially serious problem in evaluating the effectiveness of extension programs is that participants are not picked at random. Self-selection can be a problem, and it can be compounded if extension officials concentrate on the most progressive farms. This study explores the relationships between adoption of maize high-yielding varieties (HYVs) and participation in field trials intended to foster HYV usage, drawing on data from Swaziland. Results indicate that it is impossible to say if field trials had any effect on adoption. Participating farms used more HYVs, but this could have been due to self-selection or the government's selection process.
