可以理解为贸易的广度和深度,或者贸易的广义边界和集约边界,广义边界一般指新市场志的开辟和新产品的出口,集约边界一般指在同一市场原有贸易的增加.你可参考一下FEERSTERN 指数,具体计算公式有好几种,是当前贸易研究的热点.

There are many possible ways to
define the extensive margin (counting categories
exported, counting categories over a certain
size, weighting categories in various ways). We
measure the extensive margin in a manner consistent
with consumer price theory by adapting
the methodology in Robert C. Feenstra (1994),
which appropriately weights categories of
goods by their overall importance in exports to
a given country. The quality margin is not directly
observable but can be inferred by examining
projections of price and quantity on GDP
and its components. That is, if large exporters
systematically sell high quantities at high
prices, this is consistent with these exporters
producing higher-quality goods. We also show
alternatively how to interpret the projections of
price and quantity in terms of unmeasured,
within-category variety.