2.1 Human capital and regional economic development
It is widely recognised in the literature that, in addition to private benefits from human capital accruing to individual workers, there are social benefits to having a sizeable pool of individuals with high human capitals within a region (Lucas
1988; Rauch
1991). It is argued that the beneficial effects of human capital are higher in dense economic environments such as cities because face-to-face interactions between individuals are less costly and happen more frequently. Such interactions speed the transmission of new ideas and knowledge in a regional economy. An overview of the theoretical work on the mechanism involved can be found in Duranton and Puga (
2004). Moretti (
2004a) gives an overview of empirical research on these human capital spillovers. Essentially, as workers become more productive in these urban environments, higher net wages will be paid by firms, thus attracting more workers. City land rents then increase to the point where an individual migrant faces the same real wage level across the economy, thereby bringing migration towards the city to a halt (Moretti
2004b). Through this process, the externality of human capital is internalised within the economy.
Human capital spillover is the mechanism through which the human capital stock exerts its effect on the economy. Assuming the process of internalisation described above, spillovers are often studied through the development of individual wages and land rent premiums in relation to regional aggregate human capital levels, using Mincerian frameworks (Rauch
1991; Acemoglu and Angrist
2000; Moretti
2004a,
c; Glaeser and Maré
2001; Shapiro
2006). The wage effect of a relatively large supply of highly skilled workers consists of two components: a supply effect and a spillover effect. If complementarities between skill levels in the labour market are sufficiently high, and substitution between the skill levels is low, an oversupply of highly skilled workers will lead to lower wages (through lower marginal productivity) for this group. Higher wages for the other skills groups within the local economy can be expected as a result of the high complementarities. The spillover also serves to increase general productivity, for example through learning in dense environments. Any empirically measured effect of a region’s endowment of highly skilled inhabitants on skill-specific wage rates is therefore the sum of these two effects (Moretti
2004b). The positive effects on wages from the presence of a large stock of highly educated workers, as are generally found in the literature, are an indication that the spillover effect is sufficient to overcome any negative supply effect. However, greater insight is needed into the underlying mechanism. Broersma et al. (
2015) show, for example, that, for the Netherlands, an important component of the wage spillover effect results from interactions between individuals within firms rather than interactions between individuals co-located within a region.
Wage and land rent signals may, however, be distorted by institutional issues related to the functioning of labour and housing markets such as central wage bargaining and planning restrictions on real estate development. Central wage bargaining negates regional differences in productivity levels. Constraints on local real estate development make the responses of land rents to productivity shocks hard to identify. A number of studies have therefore focused specifically on the effect of human capital endowments on either skill-specific or overall employment growth.
1
Human capital spillovers do not necessarily translate into employment growth. Combes et al. (
2004) point out that technological development may be labour saving, or that labour supply may be inelastic. Suedekum (
2009) notes that the employment effects of human capital spillovers may be driven by complementarities between skills groups. Also, a relatively skill-abundant local economy may, as a result of the negative supply effect on wage rates, attract fewer additional highly skilled workers (Suedekum
2009). A variety of studies have, however, demonstrated that high human capital endowments do have positive effects on subsequent city employment growth (Glaeser and Saiz
2004; Suedekum
2009; Glaeser et al.
1995; Shapiro
2006; for the Netherlands specifically see Marlet and Woerkens
2007).
Other studies have focussed on the effects on different skills groups. For Germany, it was found that the presence of highly skilled workers has positive effects on the employment opportunities for medium and lower skilled workers (Suedekum
2009; Schlitte
2010). Berry and Glaeser (
2005), however, note an increasing accumulation of skilled workers in US metropolitan areas that are already well endowed with highly skilled inhabitants. Accumulation, or specialisation, in this context is studied by looking at the coefficient value of the lagged dependent variable in a model explaining levels or shares of human capital in cities. A value that is greater than one (the result in Berry and Glaeser
2005) implies an increasing concentration over time, but is also indicative of an explosive time series. Poelhekke (
2006) noted that these results therefore need to be interpreted with some care: the share of skilled individuals cannot increase indefinitely, something the analysis by Berry and Glaeser (
2005) suggests. Nevertheless, it was demonstrated that, in the period studied (1970–2000), skilled US cities became more skilled. This, however, was not due to the presence of skilled individuals as such. Rather, as Poelhekke (
2006) concludes based on an analysis of the same Berry and Glaeser dataset, other city-specific factors seem to be in play.
Shapiro (
2006) also notes that a positive relationship between human capital and city growth may be driven by other factors that affect both, such as amenities or the city’s industry structure. Glaeser (
1999) has pointed out those cities with high endowments of amenities have grown faster than low-amenity cities. He notes that urban rents have increased faster than wages, suggesting that the desire to live in urban areas has increased for reasons beyond productivity increases. Poelhekke (
2006) highlights the importance, as a pull factor in the localisation of skills, of the low-skilled service sector—i.e. the presence of local consumption opportunities. Bils and Klenow (
2000) find a positive relationship between educational level and economic growth at the country level, but suggest that causality might in fact run the other way: that economic growth causes an increase in the average regional education level.
Spatial mobility may be a crucial factor in this respect. It has been demonstrated that regional human capital endowments can stimulate growth, as was discussed above. However, equally, human capital has been shown to flow to regions that are doing well (Duranton and Puga
2004; Faggian and McCann
2006,
2008,
2009; Carlino and Mills
1987). This spatial mobility of human capital has consequences for its relationship with regional economic development since structural outflows of human capital can negatively affect innovative capacity (Nijkamp and Poot
1998; Faggian and McCann
2009). Rodríguez-Pose and Vilalta-Bufí (
2005) found that job satisfaction and migration measures contributed substantially to explaining regional GDP, over and above the more traditional measures of human capital endowments. Therefore, it seems that attention should be paid not just to existing endowments, but also to what attracts human capital to regions and whether these highly skilled workers are then able to utilise their skills in the regional economy.
Population and regional employment growth are thus found to be strongly related: directly through supply effects and spillovers, but also indirectly as a result of the aforementioned city-specific attractions and amenities. One line of literature has sought to more explicitly take these interrelationships into account, starting with Carlino and Mills (
1987).
2 Following this approach, Boarnet (
1994), Boarnet et al. (
2005) and Gottlieb (
1995) among others have pointed to the role that neighbouring areas play in employment and population growth. Boarnet (
1994) highlighted spatial specialisation (working against living) in multi-centric metropolitan areas and finds that employment growth depends on the population growth in nearby residential areas. Gottlieb (
1995) demonstrates that firms take the residential amenities in housing locations likely to be of interest to their staff into account in making location decisions, and that this extends to cities within commuting distance. Focussing on population growth, Partridge et al. (
2007a,
b) show that, for Canada, substantial, both positive and negative, effects may result from being close to larger metropolitan areas. In some cases, suburban areas are able to profit from providing residential opportunities for those working in the larger cities.
From this, we conclude that several factors are relevant in our study into the relationship between a city’s skills structure and the inflow of graduate human capital. Firstly, not only existing stocks but also the flows of graduate human capital are important in explaining regional development. Reverse causality may play a role, with human capital being attracted to successful regions and cities. These two variables are therefore best treated as endogenous. Secondly, it is important to control for factors that may drive both the skills structure and the inflow of graduate human capital. An important insight is that aspects that can be thought of as purely residential amenities may also affect the placement of employment. Thirdly, on the spatial scale of the Dutch city, we can expect strong interrelationships to exist between a city and other places, both close by and within commuting distances. In the next section we discuss how these matters were translated into our econometric approach.
2.2 Analysing the skills structure in Dutch cities: approach and expectations
In this study, we focus on the recursive relationship between a city’s employment skills structure and the inflow of graduate human capital onto the city’s labour and housing markets. Our analysis will be based on a sample of 287 Dutch cities, for which we have data spanning the period 1998–2008. In this section we outline our econometric approach. A discussion of our operationalisation and the dataset can be found in Sect.
3.
The main focus of our analysis is identifying the structural determinants of graduate inflow and a city’s skills structure. Therefore, in this paper, we analyse differences between cities, in terms of the spread of skills in total city employment and the inflows of human capital, rather than by considering annual growth rates.
In our modelling strategy, we have to be mindful of a number of potential econometric pitfalls. Firstly, the sought-after relationship is potentially obscured by endogeneity. In a number of similar studies, simultaneity was dealt with by lagging the exogenous variables by a considerable length of time. We model outcomes for the endogenous city-specific skills structure and graduate inflow using exogenous variables with ten-year lags.
3 We also enter the lagged dependent variable into our models.
We apply a seemingly unrelated regression (SUR)
4 model, taking into account the correlation that might exists between these equations as a result of endogeneity. We have applied the following specifications. Firstly we have an equation that defines
\(\hbox {JobHigher/Lower}_{{i},{t}+10}\)—which is total city employment at higher and scientific skill levels, relative to the total number of jobs at medium, lower or elementary levels, in city
i at time
t:
$$\begin{aligned} \hbox {JobHigher/Lower}_{{i,t}+10}= & {} \beta _{0}+ \beta _{1}\hbox {GrWork/Liv}_{{i,t}}+\beta _{2}\hbox {WCGrWork/Liv}_{i,t}\\&+\beta _{3}\hbox {JobHigher/Lower}_{{ i,t}} + X_{{i,t}}\theta +\varepsilon _{{i,t}+10} \end{aligned}$$
with
i denoting the city index,
\(i = 1,{\ldots },287\); and
t the year of observation.
\(\hbox {GrWork/Liv}_{{i,t}}\) denotes the lagged key explanatory variable. It is computed as the ratio of the inflow of recent graduate human capital into the city’s labour market to the inflow of recent graduate human capital into the city’s residential area. All other explanatory variables in the model are lagged to the base year and taken to be exogenous. We include a spatial lag of the key explanatory variable
\((\hbox {WCGrWork/Liv}_{{i,t}})\) following Boarnet (
1994) and Boarnet et al. (
2005).
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\(\hbox {JobHigher/Lower}_{{i,t}}\) denotes the lagged dependent variable, which is intended to control for persistence in the city skill structure. Matrix
\(X_{{i,t}}\) contains the other exogenous variables
6 for city
i, such as the education breakdown of the resident population—with the share of medium educated omitted, city size, labour and housing market characteristics and the number of graduates from a local higher education institution, plus spatially lagged values for a number of these variables. We also include year dummies.
The second equation describes the endogenous variable
\(\hbox {GrWork/Liv}_{{i,t}+10}\), in which
\(\hbox {JobHigher/Lower}_{{i,t}}\) is entered as main explanatory variable. The equation otherwise has a similar structure as the employment skills structure equation, including a lagged dependent variable, and the matrix
\(X_{{i,t}}\) containing a set of additional exogenous variables:
$$\begin{aligned} \hbox {GrWork/Liv}_{{ i,t}+10}= & {} \gamma _{0}+\gamma _{1}\hbox {GrWork/Liv}_{{ i,t}}+\gamma _{2}\hbox {WCGrWork/Liv}_{{ i,t}}\\&+\gamma _{3}\hbox {JobHigher/Lower}_{{i,t}} + X_{{ i,t}}\xi +\eta _{{i,t}+10}. \end{aligned}$$