1. Nick Bloom, Stanford University, Labor Topics, 2011 1 LABOR TOPICS Nick Bloom Skill Biased Technical Change (SBTC)

2. Nick Bloom, Stanford University, Labor Topics, 2011 2 Why care about skill-biased technical change? It is a major topic in the literature – over 100 papers in the last two decades. There are a number of outstanding questions on this that careful micro-data work can address Key political phenomena – Governments around the world have faced criticism that while their economic policies have increased the distribution of earnings (or employment).

3. Nick Bloom, Stanford University, Labor Topics, 2011 3 Why this SBTC occurred Skill Biased Technical Change (SBTC) Changes in wage equality

4. Nick Bloom, Stanford University, Labor Topics, 2011 4 Wage inequality over time Source: Autor, Katz and Kearney (2008, RESTAT)

5. Nick Bloom, Stanford University, Labor Topics, 2011 5 Wage inequality has been rising over time In the US wage (and consumption) inequality has risen since the 1960s Note the fall in female wage discount despite rising labor participation Source: Autor, Katz and Kearney (2008, RESTAT)

6. Nick Bloom, Stanford University, Labor Topics, 2011 6 What about by educational group: college/high school Source: Autor, Katz and Kearney (2008, RESTAT) Residual inequality is the variance of the error term (e i,t ) from a Mincer wage equation:Log(w i,t ) = α+βX i,t +e i,t

7. Nick Bloom, Stanford University, Labor Topics, 2011 7 This occurred throughout the period from 1960s Source: Autor, Katz and Kearney (2008, RESTAT) Note: The CPS data is available both from the NBER data section, and Census data from the Michigan IPUMS data site. Residual inequality is the variance of the error term (e i,t ) from a Mincer wage equation:Log(w i,t ) = α+βX i,t +e i,t

8. Nick Bloom, Stanford University, Labor Topics, 2011 8 This increase in inequality was particularly a phenomena of top half of the earnings distribution Source: Autor, Katz and Kearney (2008, RESTAT)

9. Nick Bloom, Stanford University, Labor Topics, 2011 9 Inequality also rising across educational groups Source: Autor, Katz and Kearney (2007, RESTAT) In a standard Mincerian regression the returns to a year of education rose from about 7.5% in 1980 to about 10% by 1995.

10. Nick Bloom, Stanford University, Labor Topics, 2011 10 At the same time the quantity of skills has increased Source: Acemoglu (2002, JEL)

11. Nick Bloom, Stanford University, Labor Topics, 2011 The increase in skills happened both across and within industries 11 Autor, Katz and Krueger (1998, QJE)

12. Nick Bloom, Stanford University, Labor Topics, 2011 The skills increase also happened within plants 12 Source: Dunne, Haltiwanger and Troske (1997, Carnegie Rochester Conference Series )

13. Nick Bloom, Stanford University, Labor Topics, 2011 13 The international evidence SBTC seems to have afflicted both global superpower nations The UK experienced similar wage & employment trends as the US Canada and Australia also experienced a similar phenomena Across Europe there has been a more moderate wage experience – but typically more inequality in unemployment This seems to be consistent with the idea that institutions constrained wages changes in Europe so movements in unemployment occur instead

14. Nick Bloom, Stanford University, Labor Topics, 2011 14 Why this SBTC occurred SBTC caused this change in inequality Changes in wage equality

15. Nick Bloom, Stanford University, Labor Topics, 2011 15 What has caused this within and between group changes in inequality? A summary response (1)Technology changes in much of the 20 th century have been skill biased (2)This SBTC may have accelerated since the 1970s (3)The supply of skilled workers accelerated in the 1970s but slowed from the 1980s onwards Thus, skills demand has outstripped supply, particularly since the 1980s, raising between group (high/low education) inequality The same phenomena has also probably also occurred for unmeasured skills, raising within group inequality from 1970s onwards

16. Nick Bloom, Stanford University, Labor Topics, 2011 16 Why has technology been skilled biased (1/2)? There is no need for technological changes to be skill biased The industrial revolution in England increased the use of factories employing low skilled workers at the expense of craftsmen Luddite rebellions of 1811 and 1812 were in response to falling wages of skilled weavers as factories replaced traditional weaving Ned Ludd – probably a fictional character but the movement was a major issue for the British, and even during the Napoleonic wars required extensive troops to surpress

17. Nick Bloom, Stanford University, Labor Topics, 2011 17 Why has technology been skilled biased (2/2)? The support for 20 th Century SBTC is empirical – there has been a massive increase in the supply of skills (educated workers) at the same time as skilled wages has risen, at least since 1970s. This has happened in every sector of the economy – so a universal rise in both the quantity and price of skills. This must be a demand shift Evidence that SBTC driven earlier in the century due to electrification (Goldin & Katz, 1998 & 2007)

18. Nick Bloom, Stanford University, Labor Topics, 2011 18 Over the 20 th century skills premia has fluctuated Source: Goldin & Katz (2007) Variation in returns mainly due to change in relative supply of skilled and unskilled workers

19. Nick Bloom, Stanford University, Labor Topics, 2011 19 Also an interesting sharp-post war contraction in inequality – the Great Compression Goldin and Margo (1992) argue arises because of: Supply: Increased university enrollment (GI Bill), Demand: Increase in non-skilled labor demand from manufacturing Institutional: Unions strong post-war (low unemployment) and National War Labor Board

20. Nick Bloom, Stanford University, Labor Topics, 2011 20 Modeling the increase in returns to skills The traditional Solow model is skill neutral in technical change: Y=AK α L β H γ But the prior evidence suggests a strong skill biased component.

21. Nick Bloom, Stanford University, Labor Topics, 2011 21 Skill Biased Technical Change (SBTC) Can extend the Solow model to for skilled and unskilled labor L=[(A s L s ) σ + (A u L u ) σ ] 1/σ <1 SBTC in this setup would be the ratio A s /A u rising over time Can substitute into a production function & re-arrange in terms of wage premium. Katz and Murphy (1992, QJE) did this and estimated the following regression implied by this production function: Ln(W s /W u )= β 0 + β 1 (L C /L HS ) + D t + e t They found β 1 -2/3 and D t about 2.5% (2% on figures to 2005) Suggests that labor supply clearly matters, but there has been a steady trend favoring skilled labor over the last 40 years.

22. Nick Bloom, Stanford University, Labor Topics, 2011 22 Trends in college/high-school labor supply Source: Acemoglu and Autor, (2010) Skill rose strongly in 1970s because: Vietnam draft laws Higher education expansion interacting with post-war baby boom Can see 1970s rise in skills supply and falls in relative skilled wages against long-run trend

23. Nick Bloom, Stanford University, Labor Topics, 2011 23 Katz & Murphy (1992) results (updated by AA 2010) Source: Autor, Katz & Kearney (2008, RESTAT) Once you detrend skills supply and relative wages the relationship is clear. Need to interpret cautiously, though, as only about 40 observations with serially correlated errors So predicted college/high school wage gap from a trend plus college/high-school skills supply looks a good fit But - need to interpret cautiously, as only about 40 observations with serially correlated errors

24. Nick Bloom, Stanford University, Labor Topics, 2011 24 Why this SBTC occurred SBTC caused this change in inequality Changes in wage equality

25. Nick Bloom, Stanford University, Labor Topics, 2011 25 Why did this SBTC occur?

26. Nick Bloom, Stanford University, Labor Topics, 2011 26 Why did this SBTC occur - summary? (1)Proximate cause appears to be cheaper capital and/or computers (2)But why is this skill-biased? Several arguments: a)Skills directly complement capital b)Skills directly complements computers c)Skills needed for rapid change – post 1970s had rapid change (3)Other factors that appear to play an additional (more minor) role: Labor market institutions (minimum wage and Unions) Trade with developing countries, e.g. China (4)But why did capital (particularly PCs) become cheaper? One view is the direction of technology is endogenous – the rise in skills promoted SBTC to occur

27. Nick Bloom, Stanford University, Labor Topics, 2011 27 (a) Capital complementarity (1/2) One plausible idea is that capital is more complementary to skilled labor then unskilled labor. Krussell, Ohanian, Rios-Rull and Violante (2000, Econometrica) Y=K α (λ[μK s ρ + (1-μ)L s ρ ] σ/ρ + (1- λ )L u σ ) 1/σ If σ>ρ then reductions in the cost of K increase the demand for L s Effectively this replaces A s /A u with the price of capital

28. Nick Bloom, Stanford University, Labor Topics, 2011 28 (a) Capital complementarity (2/2) Krussell et al. (2000) then provide evidence for a long-run fall in the cost of capital providing results for the model matching the data So neat model and plausible results. But there is an identification problem as the impact of the cost of capital is killed by a time trend (Acemoglu (2002, JEL), so can not be certain.

29. Nick Bloom, Stanford University, Labor Topics, 2011 29 (b) Computer capital complementarity (1/3) Worker-level evidence Krueger (1993) shows that people using computers earn higher wages, and this wage premium has increased over time. Consistent with computers playing an important role, but also with computers proxying unobserved skills – for example DiNardo and Pischke (1997) show similar phenomena is true for pencils. R&D also correlated 0.8 with computer use Machin & Van Reenen (1998) Computers or pencils?

30. Nick Bloom, Stanford University, Labor Topics, 2011 30 (b) Computer capital complementarity (2/3) Industry level evidence A number of papers also show that: All industries show an increase in skills demand and skill premium This rise is faster in industries increasing computerization faster The drawback to this evidence is that: Unobserved – could have been something else driving both Increase in computerization in the 1980s also predicts skills premium increases in the 1960s In summary, appears likely computerization is strongly linked with SBTC, but hard to prove definitively

31. Nick Bloom, Stanford University, Labor Topics, 2011 31 (b) Computer capital complementarity (3/3) Most recently Autor, Levy and Murnrane (2003) use the Dictionary of Occupational Titles to allocate cognitive and manual repetitive and non- repetitive tasks to jobs Idea is repetitive tasks can be replaced by computers, non- repetitive ones can not Find that wages and employment in repetitive tasks fallen fastest – leading to a polarization of employment: lovely and lousy jobs as christened by Goos and Manning (2008) for the UK

32. Nick Bloom, Stanford University, Labor Topics, 2011 32 Source: Autor, Katz and Kearney (2007, RESTAT) Evidence that employment is polarizing since the early 1990s – employment growth strongest below 30 th percentile above the 75th The polarization of employment (US data)

33. Nick Bloom, Stanford University, Labor Topics, 2011 33 Source: Acemoglu and Autor (2010, HLE) The polarization of employment (International data)

34. Nick Bloom, Stanford University, Labor Topics, 2011 34 Source: Acemoglu and Autor (2010, HLE) The polarization by occupation (US data)

35. Nick Bloom, Stanford University, Labor Topics, 2011 35 (c) Skills are needed to deal with change The Nelson and Phelps (1966) hypothesis is that change is complex and skilled people are better at dealing with this The acceleration hypothesis Consistent with evidence that higher skilled employees are increasingly in demand as firms rapidly changing technologies Problems are that periods of 1970 to 1995 are associated with sluggish TFP growth – hard to reconcile this with radical technological change So in summary seems plausible but hard to fully pin down

36. Nick Bloom, Stanford University, Labor Topics, 2011 36 What about other factors – trade unions? Trade unions have been weakening since the 1970s while the absolute level of the minimum wage fell strongly in the 1980s This almost certainly played a role in the particularly poor performance of the lower earnings quartiles in the 1980s. But: unions weakened only in the 1980s while the changes in inequality started in the 1970s unions only likely to effect lower quartiles, while higher quartiles is where most of the action was

37. Nick Bloom, Stanford University, Labor Topics, 2011 37 What about other factors – minimum wage? Real value of the minimum wage fell throughout the 1980s as this was not indexed and frequently not updated. This almost certainly played a role in particularly poor performance on the lowest quartile in the 1980s. But problems with MW as a complete story: MW only started to decline in real-value in 1980s Other countries – like the UK – had no MW until late 1990s

38. Nick Bloom, Stanford University, Labor Topics, 2011 38 What about other factors – international trade(1/2) ? Trade from China, India and other countries could also play a role? Literature generally discounts this as a major force as skill levels and high-skilled wages have risen in almost every industry (including all the non-tradable sectors) Also trade generally has limited predictive power: e.g. Berman, Bound and Griliches (1994, QJE), Autor, Katz and Krueger (1997, QJE) and Machin and Van Reenen (1998 QJE) The basic Hecksher-Olin model would not predict this within industry effects (predicts between industry effects going against within industry)

39. Nick Bloom, Stanford University, Labor Topics, 2011 39 What about other factors – international trade(2/2) ? But: Could possibly be due to outsourcing within non-tradable industries More generally the empirical evidence is primarily in late 1990s before Chinese imports really took off. Since then entire industries have virtually disappeared (furniture, toys, textiles etc..) So trade is probably an increasingly big factor: Bloom, Draca and Van Reenen (2011) finding major effects only post 2000 (particularly 2005)

40. Nick Bloom, Stanford University, Labor Topics, 2011 40 Endogeneous technical change Final question is why did SBTC occur in the 1970s? Acemoglu (1998, QJE and 2002 RESTUD) and others have a number of papers around the idea of endogenous technical change – idea that increased supply of graduates led to technical change Related idea is endogenous technical adoption – different countries adopt different technologies endogenously An interesting area of research and plausible hypothesis but with limited empirical evidence beyond particular examples like drugs (Acemoglu and Linn, 2004 QJE) and air-conditioners (Newell, Jaffe and Stavins, 1999 QJE)