摘要：Most empirical work in agricultural economics tries to explain or to project the use of agricultural inputs and outputs. The measurement of any of these is fraught with numerous difficulties. For capital, they tend to be the worst. - For all other input or output quantities some proxies are observed and collected in official statistics on an annual basis like purchases of fertilizer, production of grains, use of land and labour. For capital we can also observe yearly purchases of investment goods. Because these are used over several years, however, we cannot identify capital input with investments. Only some part of this year’s investment purchases can be imputed to represent present capital use and there is a myriad of ways to do so.
