Vertical Product Differentiation and North-South Trade Harry Flam and Elhanan Helpman The American Economic Review, Vol. 77, No. 5 (Dec., 1987), pp. 810-822         http://www.jstor.org/pss/1810210

On the Measurement of Intra-Industry Trade David Greenaway and Chris Milner The Economic Journal, Vol. 93, No. 372 (Dec., 1983), pp. 900-908         http://www.jstor.org/pss/2232755

Vertical and Horizontal Intra-Industry Trade: A Cross Industry Analysis for the United Kingdom David Greenaway, Robert Hine and Chris Milner The Economic Journal, Vol. 105, No. 433 (Nov., 1995), pp. 1505-1518        http://www.jstor.org/pss/2235113

U.S. Protection and Intra-Industry Trade: The Message to Developing Countries Edward John Ray Economic Development and Cultural Change, Vol. 40, No. 1 (Oct., 1991), pp. 169-187        http://www.jstor.org/pss/1154522