An interesting conversation arose on a listserv I monitor about someone doing industry research at the SIC level. This led to conversations about why. I wrote:
NAICS was supposed to supersede SIC as of the 1997 Economic Census.
SIC, last updated in 1987, won't be revised, but NAICS will, every five years (2002, 2007).
That said, a lot of data are still in SIC.
Someone noted that the business analysts, all "recent business school grads", are only being taught SIC, not NAICS.
Others noted the D&B Market Identifiers File 516 database on Dialog uses both NAICS and SICs but other D&B products on Dialog only use SICs, as does the print D&B Industry Norms/Key Business Ratios.
The SEC still uses SIC codes, though "value-added vendors allow for searching by NAICS.
So why does SIC linger? One vendor reportedly suggested that while the government pushed for NAICS, the private sector is still happy with SICs. Companies such as D&B and RefUSA have each developed extended codes; e.g. SIC 7389-11, which differ from each other, of course.
I suspect that SIC will eventually shrink away, but may take a while. As one librarian noted: "Despite any residual warm feelings for SIC codes--extended or otherwise--that we may have, the SIC manual has no future. The Feds (OMB) are not going to revise it, whereas the NAICS codes will be updated every five years. As the years go by SICs will get more and more out of date. One only has to look at earlier SIC manuals to see how certain industries wither and flourish over the decades since the first one in 1939."