Because the data are only from respondents to the CNUS, and are not weighted (see the discussion at www.
About 88% of the plants responding to the CNUS used computer networks (see Table 1).
Production workers accounted for about one-quarter (27%) of employment among CNUS respondents in the manufacturing sector.
Plants that responded to the CNUS are substantially larger than the typical manufacturing plant.
There may also be sample bias in the reduced CNUS sample we use to estimate the two-stage model.
The 1999 CNUS was mailed to the plants in the ASM sample.