They make adjustments for three familiar problems -- the non-inclusion of household labor, the calculation of government output as equal to cost, and the treatment of R&D (and other "intangible capital") spending as an intermediate rather than capital good. The first issue is self-explanatory; the second is equivalent, for purposes of measuring growth, to an assumption of constant productivity in government; and the third means that R&D expenditures are not counted in final output. Hobijn and Steindel adjust for these problems by adding R&D-type expenditures to GDP; assuming that about one-quarter of women's wages represents the market value of foregone household labor (don't ask me how they came up with that number, or how they decided that men's household labor has no value); and assuming that government productivity grows at the same rate as for the nonfarm business sector.
Their results? For 1983-2003, the adjusted and published series correlate almost exactly (0.99) at an annual level. (This isn't surprising given how the adjusted series is constructed.) But over time, the divergence is significant -- the upward adjustments for government productivity and the faster growth of R&D expenditures compared with GDP outweigh the downward adjustment due to a rising proportion of women in the workforce. So annual growth over those two decades runs about 0.5 percentage points, or 15 percent, higher with the adjusted series than with the published one. That's not a trivial difference.
This is obviously of interest to anyone working on constructing alternative measures of GDP. But to me it raises bigger conceptual questions (questions that Hobijn and Steindel don't get into, of course, since being mainstream guys they're chasing the mirage of "welfare"). If short-term fluctuations are robust to alternative measurements but long-term growth is not, shouldn't quantitative economics focus on the former? Is there a firm conceptual basis for talking about long-term growth as something we can even measure at all? Or was Keynes right when he said,
To say that net output to-day is greater, but the price-level lower, than ten years ago or one year ago, is a proposition of a similar character to the statement that Queen Victoria was a better queen but not a happier woman than Queen Elizabeth — a proposition not without meaning and not without interest, but unsuitable as material for the differential calculus.