Our sample is biased towards the manufacturing sector, and strongly biased
towards large firms and one of central Mexico’s economic centres. A focus on
manufacturing firms appears common in existing 3PL surveys such as Van Laarhoven
et al. (2000), Lieb and Randall (1996) and Boyson et al. (1999). This observation
provides a reasonable basis for comparing our data with these studies. Besides, the
composition of the manufacturing companies in our sample closely resembles the
composition of the manufacturing sector on a national level. Our sample is only
slightly biased with regard to the food industry (8 per cent more than the national), the
fabrication of apparel (4 per cent more than the national), the chemical industry (10 per
cent more than national) and the fabrication of mineral products (8 per cent less than
the national).
Our focus on larger firms is also similar to other important published 3PL surveys,
most notably Boyson et al. (1999) and Lieb and Randall (1996), providing a reasonable
basis for comparison. Nevertheless, future studies should shed more light on the
practice of small firms, especially in countries such as Mexico where these small firms
account for a large part of economic activity.