Keywords

1 Introduction

In many places in the literature it is emphasized that concentration is a prevalent and ubiquitous feature of the geographical distribution of economic activity. This is true at all geographic levels (regional, national, international) and at all levels of industrial aggregation; with the possible exception of some primary industries. This general observation is a strong indication that there are economies connected to concentration of activities, were larger regions are premiered over smaller. There are many studies that are concerned with the sources of these economies and the effects that they have on efficiency and growth. One such effect is the translation of efficiency to wage levels. Research connected to the prevailing wage differences within nations is important for a better understanding of regional development, which in turn will have an effect on national welfare.

The regional difference in wages between larger and smaller regions can be broadly attributed to two sources. The first source is the fact that average regional productivity differs between regions. The second source is that the industrial composition differs between regions.

According to economic theory it is expected that productivity is higher in larger regions due to different kinds of economies of agglomeration. The conventional macroeconomic view is that productivity growth in turn drives wage growth. Also, larger regions are able to host a larger array of sectors compared to smaller regions. Output from sectors demanding a large local or regional market can only locate in larger regions.

Given the above discussion it is clear that there exist a basic link between market-size and diversity. The extent of diversity is limited to an upper level due to the presence of fixed costs in the individual intermediate input-producing firms. This relationship implies that the size of a region will decide the degree of diversification in intermediaries. This has an impact on the productivity of all firms in the region. Thus, agglomeration provides a large market and thereby enabling the support of a wide variety of differentiated inputs. As a result of economies of scale and increasing returns, the productivity of firms in the larger agglomerations can be expected to be higher. This gives a rationale for why many firms tend to locate in agglomerations.

This leads us to the purpose of this paper were the aim is to explain the regional differences in wages, productivity and industrial composition. The paper tests the dependence of wages, productivity and industrial composition effects on regional size which in turn is measured with a market potential measure. In addition, in the estimation we control for regional differences in education, employment shares, average firm size and self-employment.

There exists a large and expanding literature concerning the regional differences in productivity and wage rates. Ciccone and Hall (1996) was not the first study that examined the relationship between productivity and economies of agglomeration, but surely one of the most influential. In this seminal study agglomeration was approximated by economic density, calculated as employment per acre.

Since then several studies have deepened and broadened the literature in these matters. Glaeser and Mare (2001) for example used wage data to investigate the wage premium paid to workers in larger cities.

More recent studies by Ciccone (2002); Rice et al. (2006) and Combes et al. (2008) argue that spatial differences in income can be ascribed to productivity differences. Higher or lower productivity is in turn assumed to be reflected in value added per unit of labor, or in earnings. Their analyses have focused on three main explanations for spatial differences in wages and productivity: (1) agglomeration economies (2) skill or industry composition and (3) exogenous regional characteristics. This paper adheres to this literature, but extends it by introducing accessibility to Gross Regional Product (GRP) as a measure for regional market potential.

The paper is structured as follows. It continues in Sect. 2 with a more in-depth discussion on the relationship between agglomeration, productivity and industry composition. The relationship of the paper to the existing literature is discussed. Also, the selection of the control variables is discussed. In Sect. 3 the data used is presented in conjunction with a descriptive analysis. Section 4 present the empirical results from the estimated models. Section 5 offers some additional tests of the robustness of the results. The closing section summarizes the conclusions and gives suggestions for interesting future research.

2 Regional Differences in Wages

As has been briefly discussed in the introduction, regions with larger market size on average can be expected to have a higher average wage level, due to different forms of scale economies. This section will continue the arguments as well as motivate the various control variables used in the present study. Furthermore, a short description of the features of the Swedish labor market is also offered.

2.1 Agglomeration Economies

Economies of agglomeration means that cost reductions occur because economic activities are located in proximity to each other. The concept itself goes back to Weber ([1909] 1929) and Marshall (1920). Economies of agglomeration are also sometimes referred to as external economies of scale. That is, the agglomeration economies are external to the individual firms. Consequently, over time an abundance of concepts and elaborations of the general concept of agglomeration economies have evolved. (see McDonald 1997)

Ohlin (1933), categorized economies of agglomeration into four types: (1) economies of scale within the firm, (2) localization economies, which are external to the individual firm and arise from the size of the local industry to which the firm belongs, (3) urbanization economies, which are more general in that it refers to cost reductions that are external to the local industry and arise from the size of the local economy as a whole and (4) inter-industry linkages, which arise from transportation cost savings in purchases of intermediate inputs.

Before Ohlin’s categorization, Marshall (1920) had already suggested three reasons for cost reductions to occur in an agglomeration. The first reason is due to knowledge spillovers, i.e. the spread of advances/innovations in production is assumed to be influenced by distance. The second explanation is the existence of a broad market for specialized skills. Specialized employees gain from having nearby access to many jobs that match their specialty. The benefits also go in the other direction. Firms benefit from having accessibility to a large pool of specialized employees matching their requirements. The third reason is the existence of backward and forward linkages between firms that are located in proximity to each other. The proximity means that the transport of inputs and outputs will be relatively inexpensive.

Hoover (1937), later made use of Ohlin’s second and third categories, localization economies and urbanization economies, as he elaborated and popularized the two concepts. Hoover’s definitions are the ones most often used to this present day. Localization economies can be captured by independent and similar small businesses in the form of positive external economies by locating in proximity of each other. This proximity between similar firms creates a market for specialized services, which can be provided by other independent firms as long as the total demand is great enough. In addition, it is possible to build up a local pool of labor with specialized skills. In this way, the businesses can take advantage of scale economies in production without resorting to large plants. The actual advantage over large-scale plants is that independence and flexibility are retained. Urbanization economies can bring about scale advantages that benefit a wider group of businesses. If, for example, general manufacturing increases in a particular area, the business services and workforce improve in size and variety. These advantages do not only relate to one sector of industry but to all. If educational standards improve, or if trucking companies expand their route network, every business will benefit.

Further, agglomeration economies can be differentiated as being predominantly static or dynamic in nature. In general a static economy of agglomeration is associated with a onetime shift in costs or productivity whereas a dynamic economy of agglomeration influences costs and productivity through time. Dynamic agglomeration economies are usually connected to the production and use of knowledge. This is at the heart of the endogenous growth theory (Romer 1986; Lucas 1988). Knowledge spillovers are an essential ingredient in this theory and since spillovers are facilitated by proximity between people and firms concentration and agglomeration are key concepts.

The empirical literature that aims to identify the sources of economies of agglomeration is reviewed in Rosenthal and Strange (2004).

2.2 Wages and Regional Characteristics

As hinted above some sources of regional wage differences work through scale economies. But there are several different ways for those to manifest themselves. For instance, differences in wages across regions could directly reflect spatial differences in the skill level and composition of the workforce. Theory argues that the division of labor, which leads to productivity gains, is limited by the extent of the market. Then naturally, workers in larger markets may enjoy higher wages because of greater possibilities for the division of labor.

According to Combes et al. (2008) there are reasons to believe that workers may spread across employment areas so that the measured and un-measured productive abilities of the local labor force may vary. Industries are not uniformly spread across regions and they require different combinations of labor skills. Accordingly, one should expect a higher mean wage in areas specialized in more skill-intensive industries. This brings us into the discussion on industry composition and wages.

Different industries or sectors differ in their ability to pay high wages. The difference in this ability may come from the competitive situation in that particular industry or the availability of factor inputs. Since regions differ in their industry structure, it is likely that some of the regional wage differences can be explained by these structural differences. Thereby some part of the wage differences across areas reflects spatial differences in industry structure. These differences may not be directly connected to regional productivity differences.

Combes and Overman (2004) argues that failure to control for heterogeneous skill composition between regions may significantly limit the interpretation that can be given to regional differences in labor productivity or wages. Hence, higher wages or productivity might not reflect real externalities if not taking labor skill composition into account.

Non-market interactions such as technological externalities, and in particular those originating from human capital, may also play an important role in explaining wage differences between regions (Rauch 1993). Sianesi and van Reenen (2003) presents a detailed literature review which provide strong evidence in favor of the view that the amount of human capital is positively correlated to productivity. Rauch (1993) argues that the level of human capital is a local public good, hence, regions or cities with higher levels of education attainment should consequently have higher wages. Rauch base this argument on 1980 US cross-sectional data on a regional level. Glaeser and Mare (2001) suggest that urban workers are more productive because cities enable workers to accumulate more human capital. This accumulation can work through more effective knowledge spillovers, proximity between skilled workers and between knowledge-intensive firms, in regions where knowledge are abundant and dense. These spillovers rely on face-to-face contacts that are more likely to occur in such knowledge-intensive regions. Knowledge can be transmitted either as a by-product that is non-intentional or in more formal types of collaborations.

Previous studies point to yet another regional characteristic that have a positive effect on productivity and wage levels. This characteristic is firm size. The size of a firm influences the possibility to exploit internal economies of scale, and as a consequence, positively influence labor productivity. Extensive research in the field confirms that larger firms tend to pay higher wages than smaller ones; see Moore (1911), later confirmed by Mellow (1982); Brown and Medoff (1989); Troske (1999) among several others. Average firm size in a region is, hence, an important component when explaining regional wage variation. According to Glaeser et al. (1992) firm size may also affect the level of productivity if it is related to market power, where the effect itself is ambiguous a priori. A large monopolistic firm may have higher incentive to conduct R&D due to a higher probability of retrieving the returns (Romer 1990) while at the same time small firms may experience a higher market pressure to innovate in order to stay competitive (Porter 1990).

Wages should logically also be influenced by the level of (un-)employment in the region. If the scarcity of labor increases wages go up, while if it decreases they will fall. In 1994 Blanchflower and Oswald presented their book “The Wage Curve”, where they established a negative relation between unemployment and wages across regions over time.Footnote 1 Blanchflower and Oswald (1994) found that the employment elasticity of wages is, for most countries, approximately −0.1, with the US and UK being the main focus of the study. Since then several studies have been presented with mixed conclusions. A study by Albæk et al. (2000), analyzing pooled data on regional wage formation in the Nordic countries during the 1990s, systematically deviate from the results presented by Blanchflower and Oswald (1994). Even though Albæk et al. (2000) found a significant negative relationship between real wages and unemployment at the regional level, this relationship becomes unstable once accounting for regional fixed effects. The authors explain these results by the historically strong labor unions that negotiate wages at the national level in the Nordic countries. This negotiating model implies that there is only a small local wage drift influenced by the regional labor market conditions. According to Nijkamp and Poot (2005) the variation in findings within this field is a response to heterogeneity among the studies in terms of the type of data used and differences in model specification. In order to verify this Nijkamp & Poot performed a meta-analysis revealing that the wage curve is a robust empirical phenomenon. However, they also found clear evidence of a publication bias and when correcting for this bias the elasticity becomes less than −0.07.

Some emphasis should also be put on the rate of self-employment when explaining regional variations in wages. According to research, self-employment can work in dual ways when influencing regional wages. On the one hand high unemployment rates in a region may cause entrepreneurial activities, such as self-employment, to increase. This is referred to as a so called refugee effect, since the prospect of other forms of employment is small. The relationship between wage rates and unemployment is expected to be negative. On the other hand, higher levels of self-employment may be a sign of true entrepreneurial ventures, referred to as a entrepreneurial effect, which, in the long-run, will reduce unemployment Thurik et al. (2007) and hence have positive effect on the regional wage level. There exists considerable theoretical and empirical support for both of these views.

While Oxenfeldt (1943) argues that low prospects for wage-employment will cause a higher self-employment level, Audretsch and Fritsch (1994) on the contrary found that this relation is negative. In a recent study Thurik et al. (2007) tested this ambiguity by using a two-equation vector autoregression model, for a panel of 23 OECD countries over the period 1974–2002. The result reveal that changes in unemployment have a positive impact on changes in self-employment rates, while simultaneously changes in self-employment rates have a negative impact on unemployment. However, the latter effect is stronger than the first one.

In addition, due to the assumption of total labor mobility the role of amenities will according to Roback (1982) also influences regional wage differences. In Roback’s model, worker utility depends on the wage level, the price of land, and a vector of potential lifestyle or amenity characteristics. Wages and rents must adjust to equalize utility in all occupied locations. Otherwise some workers would have an incentive to move. Roback (1982) and more recent studies such as Graves et al. (1999) have included variables such as: education levels, crime rates, number of people living under the poverty line, congestion levels, local unemployment, weather conditions, population density and size etc., as proxies for the role played by amenities when investigating regional wage differences.

Criticism towards the “city size wage premium” has also been raised since it is plausible to imagine that workers with above average ability and motivation have a “lifestyle” preference for living in larger regions. Glaeser and Mare (2001) however, reject the argument that such omitted ability bias explains the city wage premium. They do so because including direct measures of ability (the AFQT test), instrumenting for place of birth, and then studying wages all fails to eliminate this wage premium.

There is also ample evidence of inter-industry wage differences that are related to institutional features such as unionization and not to productivity (Wheaton and Lewis, 2002) or industry composition.

2.3 The Functioning of the Swedish Labor Market

To enable us to fully interpret the results it is of some importance to take a closer look at the Swedish labor market and its dynamics. At the heart of “the Swedish model” is a system of collective bargaining between trade unions and employers’ associations. Sweden distinguishes itself from most other countries in that the level of membership unions and other labor markets organizations is extremely high. Due to historical traditions the Swedish labor market has become centralized. Central wage agreements are set by the labor unions and representatives from the employers to obtain low levels of income differences compared to most other countries.

Calmfors (1993a, b) argues that a highly centralized wage setting system causes wage levels to increase considerably slower compared to not so centralized systems. This leads to higher employment levels, which is at the heart of the Swedish model.

Calmfors (1993a, b) further states that the highest level of real wage increases is obtained in a system which lies in-between decentralization and centralization, i.e. wage agreements at the industry level. Up until 1983 the Swedish wage setting system was a text-book example of a highly centralized negotiation scheme (Lindgren 2006). Since then Sweden has moved towards a more decentralized system. At present, once framework agreements are set centrally for the corresponding employment sectors, individual collective agreements can be negotiated between employers and trade unions at a local level. A standard collective agreement is therefore not automatically applicable to all regions or to an entire industrial sector. The system is thus more flexible than before.

3 Data and Descriptive Analysis

As stated in the theoretical background, we assume that variation in average earnings mainly comes from two sources; (1) differences in the wage rates paid to workers in a given sector arising from productivity deviations across regions, (2) and differences in the industrial composition between regions. To be able to discriminate between these sources we use a method applied in Rice et al. (2006). Analogous to that study we decompose regional wages into two components, referred to as the productivity and industry composition indices. We do this in order to assess the impacts on these indices by agglomeration effects as well as the different control variables presented in the previous section. Swedish regional data from 2004 are used for this study, were the definition of a region is municipalities with local governments. There are 290 such regions in Sweden.

The decomposition is described in the following seven equations.

We start with four definitions (Eqs. 8.1, 8.2, 8.3, and 8.4).

$$ w_r^s = \mathrm{ wage} \ \mathrm{ in} \ \mathrm{ sector}\;s\;\mathrm{ in} \ \mathrm{ region}\;r $$
(8.1)
$$ e_r^s = \mathrm{ employment} \ \mathrm{ in} \ \mathrm{ sector}\;s\;\mathrm{ in} \ \mathrm{ region}\;r $$
(8.2)
$$ {E_r} = \sum\limits_s {e_r^s = } \;\mathrm{ total} \ \mathrm{ employment} \ \mathrm{ in} \ \mathrm{ region} \ r $$
(8.3)
$$ \sigma_r^s = \frac{e_r^s }{E_r } = \mathrm{ employment}\;\mathrm{ share}\;\mathrm{ in}\;\mathrm{ sector} \ s\;\mathrm{ in} \ \mathrm{ region} \ r $$
(8.4)

Next, using the definitions in Eqs. 8.1 and 8.2 we construct a measure for the average wage level in sector s.

$$ {{\bar{w}}^s} = \frac{{\sum\limits_r {e_r^sw_r^s} }}{{\sum\limits_r {e_r^s} }} = \mathrm{ average} \ \mathrm{ wage} \ \mathrm{ in} \ \mathrm{ sector} \ s $$
(8.5)

Using 8.2 and 8.3 we form the total employment share in sector s.

$$ {{\bar{\sigma}}^s} = \frac{{\sum\limits_r {e_r^s} }}{{\sum\limits_i {E_r } }} = \mathrm{ share} \ \mathrm{ of} \ \mathrm{ total} \ \mathrm{ employment} \ \mathrm{ in} \ \mathrm{ sector} \ s $$
(8.6)

Combining Eqs. 8.5 and 8.6 gives us the decomposed wage identity.

$$ {{\bar{w}}_r} = \mathop{{\sum\limits_s {w_r^s\sigma_r^s} }}\limits = \sum\limits_s {w_r^s} {{\bar{\sigma}}^s} + \sum\limits_s {{{\bar{w}}^s}\sigma_r^s} + \sum\limits_s {\left( {w_r^s - {{\bar{w}}^s}} \right)\left( {\sigma_r^s - {{\bar{\sigma}}^s}} \right)} - \sum\limits_k {{{\bar{w}}^s}{{\bar{\sigma}}^s}} $$
(8.7)

where \( {{\bar{w}}_r} \) is the average wage in region r. \( \sum\limits_s {w_r^s} {{\bar{\sigma}}^s} \) denotes the productivity index, where the industrial composition is assumed fixed at the average national level across regions. Thus, the variation in this index reflects the regional productivity differences. \( \sum\limits_s {{{\bar{w}}^s}\sigma_r^s} \) is the industrial composition index in which regional differences is attributed to differences in the composition of sectors in different regions. In this index the wages across sectors are assumed to be fixed at the average national level. The variation in this index represents the variation of the regional industry composition. The remaining terms in Eq. 8.7 represents the covariances between the industry employment shares and wages in region r.

Table 8.1 below presents the variables that we are using in the empirical analysis.

Table 8.1 Description of variables used
Full size table

In Figs. 8.5, 8.6, and 8.7 found in Appendix 1 the correlation between the three variables wage, productivity index, and industrial composition index and our measure of market potential is displayed. The three figures all reveal a weak but positive relation to market potential.

The correlation matrix presented in Table 8.5 naturally show strong correlations between the three dependent variables, since the indices are derived from average wage. The correlation coefficients between the dependent variables and the market potential variable, accessibility to GRP, vary between 0.559 and 0.331. Two of the control variables, average firm size and self employment have a strong correlation vis-à-vis the three dependent variables. The self employment variable is the only variable that shows a negative relationship. This seems to indicate a “refugee” effect in terms of entrepreneurial activities. Education also presents high correlation values.

Furthermore, the descriptive statistics presented in Table 8.6 in Appendix 1 show that there is a large variation in the variables across Swedish regions. This is especially true for the control variables accessibility to GRP and education, but also in terms of the average wage level itself. This supports the idea that Sweden is characterized by substantial income disparities; wages in the lowest earning region is 55 % lower than the level earned in the highest wage region.Footnote 2

On the following two pages four different maps are provided in order to show the geographic distribution of the dependent variables. All the 289 included Swedish regions have been divided into four groups depending on their performance. High performing regions are marked in darker colors, group 3 and 4 respectively The real values and level of the intervals for the four different groups can be seen in Fig. 8.8 in Appendix 2.

Figure 8.1 displays the national variation in terms of average wages. One can see that it is especially areas in the three large city regions Stockholm, Gothenburg and Malmo which are marked as top-ranking. The map suggests that agglomeration in general has a substantial correlation with earnings since all dark areas are regions where Sweden’s larger cities can be found; such as Linkoping/Norrkoping, Jonkoping and Karlstad etc. In terms of the lowest earning regions one can say that they often are rural, low populated regions with tendency to be located in the northern parts of Sweden. The fact that some of the northern regions are placed within group 3 and 4 can be explained by the high proportion of employed within the high-technology mining industry were wages traditionally has been very high.

Fig. 8.1
figure 00081

Average wage

Full size image

When it comes to productivity, Fig. 8.2 reveals that it is once again predominately the regions within the large city areas that on average have a higher productivity index compared to the rest of Sweden. Once more the smaller regions far from a large market show the lowest levels of productivity. One can also observe that some of the “mining-municipalities” has a lower productivity level compared to wage, which can support the idea that there is a wage-premium in these areas to enable them to attract labor.

Fig. 8.2
figure 00082

Productivity index

Full size image

Figure 8.3 illustrates the geographical variation in terms of industry composition were more or less the same pattern is found as in terms of the wage and productivity distribution.

Fig. 8.3
figure 00083

Industry composition index

Full size image

Finally, in Fig. 8.4 the accessibility to GRP clearly show that southern Sweden has a higher market potential than the south, this is most pronounced for regions situated in proximity to either Stockholm, Gothenburg or Malmo. All of the regions within these city areas belong to the highest rated group. The further away you get from these areas you will experience a fall in accessibility and market potential. Spikes in accessibility is then found in those regions that host medium-sized cities; e.g. Linkoping/Norrkoping, Jonkoping and Karlstad.

Fig. 8.4
figure 00084

Accessibility to GRP

Full size image

4 Empirical Results

Next let us turn to the empirical analysis of regional wages, productivity and industry composition. In the empirical models the estimated parameters are expressed as elasticities since all variables are logged.

The regression models to be estimated are:

$$ ln \ wage = {\beta_0} + {\beta_1}ln \ Fsize + {\beta_2}ln \ Semp + {\beta_3}ln \ Edu + {\beta_4}ln \ Empshare + {\beta_5}ln \ AccGRP + \varepsilon $$
(8.8)
$$ ln \ prod = {\beta_0} + {\beta_1}ln \ Fsize + {\beta_2}ln \ Semp + {\beta_3}ln \ Edu + {\beta_4}ln \ Empshare + {\beta_5}ln \ AccGRP + \varepsilon $$
(8.9)
$$ ln \ comp = {\beta_0} + {\beta_1}ln \ Fsize + {\beta_2}ln \ Semp + {\beta_3}ln \ Edu + {\beta_4}ln \ Empshare + {\beta_5}ln \ AccGRP + \varepsilon $$
(8.10)

In order to check the robustness of the findings, the regression models are tested using three different methods. First a standard OLS approach is applied followed by spatial lag (SL) and spatial error (SE) models, adjusting for possible spatial autocorrelation. The SL and SE results can be found in Appendix 3. Additionally, instrumental variable (IV) estimation is applied to test for possible endogeneity problems.

4.1 Ordinary Least Squares

Table 8.2 below presents the OLS results for all the three regression models.

Table 8.2 Estimation results using OLS
Full size table

In Table 8.2, the OLS regression estimates are presented. The results clearly show that the three dependent variables, average wage, productivity and industry composition indices are significantly linked to the regional attributes.

The table displays that market potential, which is measured as accessibility to GRP, affects both productivity and industrial composition, and hence, the regional variation in average wages. The estimated elasticities reveals that a twice as large market potential is expected to have approximately 1.7 % higher wages. The productivity index is expected to be 1.8 % higher, and the industrial composition index is expected to be 0.9 % higher.

When comparing these results to earlier studies made in other countries, the elasticities seem to be lower in the case of Sweden. Factors that can explain this is (1) the use of accessibility to GRP as a measure of market potential, and (2) the functioning of the Swedish labor market, were wage differences traditionally has been comparatively low.

Table 8.2 also reveals how the control variables influence the regional variation in the dependent variables. As can been observed, all of the variables, with the exception of industry composition in relation to education, turn out to have a significant effect on wages, productivity and industry composition, respectively.

The results show that educational level in municipalities influence wages. It is, however, the productivity index which is most influenced by a high share of educated people in the region with an elasticity of 10.5 %, while there is no influence on the industrial composition index.

The second explanatory variable is average firm size in each municipality, which also turns out to have a significantly positive effect on all three dependent variables. Yet as in the case of education, the effect is found to be smallest for the industrial composition index. The results points to that there are significant effects from scale economies which are internal to the firms.

When it comes to the share of employed persons within the municipality the results are similar to that of the firm size variable. Higher competition among the employers to attract labor seems to increase wages.

The final control variable is the share of self-employed persons in a municipality. For all three dependent variables the effect is negative and significant. In particular, the negative influence is found to be the largest in terms of average wages. This supports the so called “refugee effect” discussed in earlier sections. Another explanation for the negative relation can also be the structure of the data set, were one cannot separate between incomes from self-employment or regular employment. For example an individual running his/her own business can withdraw or withhold money in irregular intervals, which implies that 1 year the dividend might be very high while being very low in a second period. If many self-employed chose to use the firm dividend to take out a small proportion as income during our reference year, this could then affect the outcome.

The explanatory powers of the regressions are very high for average wage and productivity where the R2 is 71 % or higher. The weaker relationship for industry composition is confirmed by a lower R2.

4.2 Testing for Endogeneity: IV Results

A problem connected to an analysis of the role played by agglomeration for productivity and income, relates to the fact that it is very hard to differentiate between two possible explanations for a positive correlation between productivity and agglomeration. Productivity and income may be high because of agglomeration effects; which is the underlying idea in this paper. However, there is also a possibility that agglomeration arises due to the fact that wages and productivity are high due to for example a positive regional specific shock which in turn attracts labor and firms. A recent study by Fu and Ross (2007) tests the above stated endogeneity problem; if wage premiums in clusters are caused by agglomeration economies or of regional characteristics, such as labor heterogeneity. Their result show that the causality runs from agglomeration to wage, and not the other way around.

However, if any of our local characteristics is endogenous in relation to the dependent variables, our models might omit unobserved abilities that will influence the results. If such omitted variables are also correlated with any right hand side variables, then a bias can result. Reverse-causality is hence potentially still a problem which must be tested for.

Furthermore, due to the model set-up another possible bias might arise. The reason is that we do not fully control for the type of labor or firms that are located in the agglomerations, hence there may be a selection bias present. Since some people and firms are more productive than others, this can result in varying levels of productivity and wages. This could explain the wage premium found in larger regions if we assume that more high-performing firms and individuals are located there. A study by Combes et al. (2009) however, confirms that productivity differences, and thus wage differences, predominantly can be explained by the presence of agglomeration economies.

The choice of the instruments is based on the assumption that the instrumental variables represents an exogenous regional characteristic that has lasting influence on localization decisions, and thus on agglomeration, but not on the present level of productivity and income. The instruments chosen are therefore: (1) municipal 1950 population, (2) population 1950 within 1 h driving distance, (3) municipal land area, (4) land area within 1 h driving distance, (5) dummies for municipalities belonging to Stockholm, Gothenburg and Malmo regions. The validity of these instruments refers to that they all in some way reflect the potential market size of a region. See Table 8.3 below for the IV results.

Table 8.3 IV Estimation results for the wage equation
Full size table

The IV estimates corroborates the findings from the OLS regressions presented in Table 8.2. However, when comparing the results to the OLS estimates there are some deviations in the elasticities for the control variables. In a majority of the cases the deviations among the elasticities are within the +/− 0.2 to 0.8 percentage bound. Especially it is for the self-employment, employment share and average firm size were the largest variations in comparison to the OLS results occur. The negative effect of self employment on average wages is 1.2 % higher than when estimating without instruments.

As stated earlier we have also used different spatial estimation techniques for both the OLS and IV regressions. Even though tests have indicated that there may be some problems with spatial regimes the results from these regressions do not differ in any significant way from the OLS estimations. (see Appendix 3, Table 8.7, 8.8, 8.9, 8.10, 8.11, and 8.12). This confirms the robustness of the results.

In summary we confirm earlier research by concluding that denser, larger firm dominating, more educated, and high employment areas are characterized by a higher wage on average.

5 Conclusion

The focus of this study has been to estimate regional agglomeration effects in Sweden. We have investigated how concentration and agglomeration influence regional wage levels. In addition, the regional average wage level has been decomposed into a regional productivity index and a regional industrial composition index.

In the productivity index the industrial composition are held constant and the average wage in a region is only influenced by the regional wage level per sector. The industrial composition index on the other hand, is calculated holding industrial sector wages constant across regions. The index is thus only influenced by industry composition. Using these indices we control for the fact that regions have different industry compositions and that the average regional productivity differs between regions.

In the empirical estimations we use the average regional wage level and the two indices as dependent variables. The major explanatory variable is our measure of agglomeration. As a proxy for agglomeration we use accessibility to gross regional product (GRP). This accessibility is calculated using municipal GRP for all regions and discounting them in space according to the driving time distance. Therefore, the measure takes into account both size effects and the spatial layout of the municipalities.

Also, in the regression analysis we control for other factors that may influence wage, productivity and industrial composition effects. These control variables are the education level in each municipality, the share of the working age population that holds a job, average firm size and the degree of self-employment.

The general result of the analysis is that economies of agglomeration are a prevalent feature across regions in Sweden. The results indicate that regional size (as measured by accessibility to GRP) influences productivity as well as industrial composition, and hence, the regional variation in average wages. The estimated elasticities show that a twice as large region is expected to have approximately 1.7 % higher wages. The productivity index is expected to be 1.8 % higher, and the industrial composition index is expected to be 0.9 % higher.

With reference to similar studies in other countries our estimated elasticities appear small. There are at least two factors that can potentially explain this result. The first is dependent on how agglomeration itself is measured. We use an accessibility measure while in the literature it is more common to use variables measuring regional size or density. The other factor has to do with the distribution of wages in Sweden. It is a well known fact that wage disparities are relatively small in Sweden. Wages are set in a collective bargaining between different unions and employer organizations.

Turning to the control variables, the education level in municipalities influence wages and, in particular, the productivity index (about twice as large effect), while there is no influence on the industrial composition index.

The share of employed people has a significant effect on all three dependent variables, but the size of effect on the industrial composition is about one third of the size compared to the other two.

The average size of the firms in each municipality has a significantly positive effect on all three dependent variables, but once again, the effect is the smallest for the industrial composition index. This points to that there are significant effects from scale economies that are internal to the firms.

The last explanatory variable is the share of self-employed people. For all three dependent variables the effect is negative and significant. In particular, the negative influence is the largest on the average wages.

In the estimation we have used some different spatial estimation techniques. Even though tests have indicated that there may be some problems with spatial regimes the results from these regressions do not differ in any significant way from the OLS estimations.

In addition, in the empirical analysis we have also used an instrumental variable approach to investigate possible bias from reverse causality from the dependent variables to the independent ones. Results indicate that this bias is probably small.

In this study, we have estimated relationships for the aggregate economy. Of course, it is quite possible that agglomeration effects differ between industries. Therefore, one way forward is to perform this kind of analysis on industrial aggregates. Especially, it should be interesting to compare different kinds of service sectors since it can be argued that they are more dependent on proximity to larger markets. Also, sectors with a high knowledge or R&D intensity may have more to gain from agglomerations, where knowledge spillovers can be expected to be more important.

One other possible way to continue and broaden the analysis is make use of the fact that our agglomeration proxy has the form of an accessibility variable. Since this variable is calculated using the time distance of the road network between municipalities it is possible to assess effects on wages, productivity and industrial composition from changes in the quality of the road infrastructure.