How much of US productivity growth comes from the IT sector?
Core argument: The IT sector's total factor productivity rose 178% over the 36 years since the start of 1988, versus 12% for all non-IT sectors combined, while aggregate TFP increased 40%.
For a given % change in any particular sector’s TFP, the effect on aggregate TFP is equal to the sector-level change multiplied by a weight equal to the ratio of that sector’s nominal gross output to the total nominal value added of the entire private business sector. The total change in aggregate TFP is the sum of the weighted changes in sector-level TFPs. The “Domar weights,” [which] sum to more than one since the numerator includes sales of intermediate goods instead of only value added, incorporate the effects of sectoral linkages—when sector i becomes more productive, the sectors that use the output of sector i become more efficient and expand production, as do the sectors that use the output of those sectors as inputs (including possibly sector i), and so on. Fig.3, panel A shows that aggregate TFP has increased by a factor of 1.4, or 40%, in the 36 years since the start of 1988, while the IT sector’s TFP has increased by a factor of about 2.78, or 178%. In contrast, TFP in all the non-IT sectors combined has increased by a factor of only about 1.12, or 12%. Fig.3, panel B shows that the IT sector has contributed approximately 17 percentage points to cumulative TFP growth since 1988, and the non-IT sectors about 20 percentage points. Thus the IT sector accounts for roughly 45% of cumulative aggregate productivity growth.

