Fewer than half of all 4-digit SIC categories have direct NAICS counterparts or can be reconstructed by adding whole NAICS codes together. Another group can be approximated within 3 percent of sales using whole NAICS codes. You can identify which these are by looking for the
(almost comparable) symbols in the Bridge Between NAICS and SIC
. For the remaining SIC codes, identified with
(not comparable), the bridge data allow you to determine what proportions of particular NAICS contribute to a given SIC. Note that any proration you do is subject to considerable error, and prorating on sales or employment may give significantly different results.