21COE, University of Tokyo

MMRC Discussion Paper No. 39

MMRC
DISCUSSION PAPER SERIES

MMRC-F-39

Productivity Convergence at the Firm Level
Before March 31

Faculty of Economics, University of Tokyo, andEconomic and Social Research Institute, Cabinet Office,
Government of Japan
After April 8

Policy Board, Bank of Japan
Kiyohiko G. Nishimura
Faculty of Business and Commerce, Keio University
Takanobu Nakajima
International Graduate School of Social Sciences, Yokohama
National University
Kozo Kiyota
March 2005

Productivity Convergence at the Firm Level
Kiyohiko G. Nishimura †Takanobu Nakajima ‡Kozo Kiyota§
March 12, 2005

Abstract
Productivity convergence among countries has been investigated extensively with mixed
results. This paper extends the analysis to the firm level to shed light on the debate ofconvergence or non-convergence. We find productivity convergence among firms widelyin Japan, in both manufacturing industries and non-manufacturing ones. We obtain theseresults taking explicit account of exiting firms as a source of selection biases. The convergence rate is much faster among firms than countries. We also find that there are substantial
differences among industries in the convergence speed. IT industries that heavily rely ontechnological progress show faster rates of convergence.
Key words: firm-level productivity, convergence, technology diffusion, selection bias
JEL classification code: D21 (Firm Behavior); D24 (Production; Capital and Total
Factor Productivity; Capacity); O47 (Measurement of Economic Growth; Aggregate Productivity); L11 (Production, Pricing and Market Structure; Size Distribution of Firms)

 Views expressed here are strictly personal and in no way represent those of Economic and Social ResearchInstitute, University of Tokyo, Keio University, or Yokohama National University. This paper is a part of ourongoing joint research with Flora Bellone, Patrick Musso, and Michel Quéré of Institut de Droit et d’Economie dela Firme et de l’Industrie.
†
Faculty of Economics, University of Tokyo and Economic and Social Research Institute, Cabinet Office,
Government of Japan‡ Faculty of Business and Commerce, Keio University§ International Graduate School of Social Sciences, Yokohama National University¶ Takanobu Nakajima, Faculty of Business and Commerce, Keio University, 2-15-45 Mita Minatoku, Tokyo,108-8345, Japan; nakajima@fbc.keio.ac.jp, +81-3-5427-1231(Tel), +81-3-5427-1578(Fax).

1

Introduction“Comparisons of productivity performance across countries are central to many of the questions concerning long-run economic growth” (Bernard and Jones, 1996, p. 1216). Thus, there
has been a large body of literature that investigated cross-country productivity convergence bothat the country level (Dollar and Wolff, 1988; Dorwick and Nguyen, 1989; Wolff, 1991) and at
the industry level (Baumol, 1986; Bernard and Jones, 1996; Pascual and Westermann, 2002).
Bernard and Jones found little evidence of convergence in manufacturing. 1 Others have obtained results that support productivity convergence in countries with lower productivity at theinitial period but growing rapidly in the subsequent periods.
However, it should be noted that the growth of a country results from the growth of industries, which comes from the growth of firms. Ultimately, the productivity growth of a country is
attributed to the productivity growth of firms. Thus, to examine characteristics of across-country
productivity convergence, it is of the utmost importance to examine characteristics of the productivity convergence among them. If productivity convergence is important across countries,
it should be all the more important within a country.
In spite of this importance, there has been little empirical work at the firm level on productivity convergence whose scope is wide enough to cover a major part of an entire economy,
including not only manufacturing but also non-manufacturing sectors. This wide coverage isnecessary to assess macroeconomic effects of technology diffusion. Although there are somerecent studies of productivity convergence at the firm or establishment levels, they are also
narrow in their scope in that the studies only focused on manufacturing sector. 2This paper fills this gap between theory and empirical analysis. We examine the growth of
productivity at the firm level using a large-scale data base of firms, covering not only manufacturing but also non-manufacturing industries. The data used in this paper is a micro databaseof firms called Kigyou Katsudou Kihon Chousa Houkokusho (The Results of the Basic Surveyof Japanese Business Structure and Activities) prepared by the Research and Statistics Depart1 However, their finding is controversial. Sørensen (2001) criticized in his comment that the established evi-

dence of non-concurrence in manufacturing by Bernard and Jones heavily depended on the choice of base year.
Pascual and Westermann (2002) stressed the importance of similar technologies in productivity convergence, disaggregating the industry classification in more detail.
2 For instance, see Fukao and Kwon (2004) for Japan and Griffith, Redding and Simpson (2002) for the United
Kingdom.

1ment, Ministry of Economy, Trade and Industry (METI) for the period 1994-2000.
This paper is, to the best of our knowledge, the first study to analyze technology diffusion
with careful consideration on the effects of entry/exit. Note that countries hardly enter/exit
while firms often do. Recent studies by Aw, Chen and Roberts (2001) and Kimura and Kiyota(2004) confirmed that not only firms’ own productivity growth but also entries/exits playedlarge roles in aggregate (national-level) productivity growth. This paper shows that the analysis
without taking account of the effects of exits causes a 1.5 percent point downward bias in the
speed-of-convergence.
The results of this paper indicate that there exists strong evidence of productivity convergence among firms in most industries. Further, the speed of convergence of firms is faster thanhas been observed in previous national- or industry-level studies which indicate an average 10.3
percent annual rate.
This paper is organized into five sections as follows. The next section explains the model,
data and econometric issues. Section 3 reports the estimation results of the baseline model. Section 4 discusses the results obtained in this paper, with special emphasis on industrial differencein the speed of convergence. The final section concludes the paper.

2

Productivity Convergence among Firms

2.1 Model
The simple model of productivity convergence proposed by Bernard and Jones (1996)is our initial model. This model has been extensively utilized in the studies of cross-country productivity
convergence studies. It has also been employed in recent establishment- or firm-level productivity studies (Fukao and Kwon, 2004; Griffith, Redding, and Simpson, 2002). The strength of
this approach is that the specification does not depend on the form of production function.
Let us denote TFP (total factor productivity) for a firm i in year t by

it . The TFP growth isassumed to be described as:ln i ti  ln 1t 1  ln it 1  ln i t 1  ln it (1)where ln 1t 1  ln i t 1 represents a catch-up variable, which represents the distance in productivity between firm 1 with the highest productivity and firm i. The speed of catching-up
2

therefore is captured by  while the asymptotic rate of productivity growth of firm i is denotedby i . Finally, ln it represents the disturbance term.3
This framework yields the following catch-up path of productivity:

where itln i tii t 1t , respectively. In the long-run, the annual average TFP

it  1t and it 1  1   ln it 1  ln it 

growth rate of firm i relative to firm 1 between year 0 and year T is written as1
ln i T  ln i 0 TT 1  1T  ln i0  T1

T

1

1

 T

i

 1  ln i This is the basis of familiar convergence models of long-run average growth on initial level andwe specify a baseline model as follows.
ln iT1ln i T  ln i 0 Twhere catch-up is denoted by a negative coefficient ofiT N 0 .

0 1 ln i0  i T 
1(2)

1  1  T  T . We assume

2.2 Econometric Issues
The standard procedure of a cross-country productivity convergence is to estimate equation (2)and then to get the estimate of the speed-of-convergence  from the estimate of

1 . However,this procedure cannot be applied to cross-firm convergence directly, since we have a problemof data truncation in firm data that is not present in country data. In the case of country data,
whether or not a particular country is in the data set we consider is not correlated to the country’s
productivity level. In contrast, whether or not a particular firm is in the data set is quite likely to
be correlated to the firm’s productivity level. If a particular firm’s productivity goes under somethreshold level, this usually implies a serious profitability problem for the firm. Then, the firm
is likely to be closed down and/or bankrupt so that it drops out of the data set we consider. This
3 There are other factors influencing productivity movement, such R&D activities and patent purchases.

In acompanion paper (Nishimura, Nakajima and Kiyota, 2005), we explicitly consider effects of these factors. However, for the sake of simplicity, we assume that effects of these factors are represented by the disturbance termln it .

3

correlation between data truncation and productivity may produce a well-known bias of sample
selection if we estimate equation (2) by an ordinary least squares (OLS). 4
Let us consider firms’ entry and exit patterns between year 0 and year T , which are classified
into three types as summarized in Table 1. Type-1 firms are survivors that continue to stay in themarket between year 0 and year T . Type-2 firms are exiters that stay in year 0 but exit from themarket before year T . Type-3 firms are entrants that start their business after year 0. Whether
or not productivity is observed depends on the patterns of entry and exit. The entry and exit
variations lead to the missing data for the dependent or independent variables. This is often
called a sample selection problem.
Table 1: Entry, Exit, and Observability of Variables
Year 0Year T

i0

iT

x i0

yiT

Type-1 Survivors

observable

observable

observable

observable

Type-2 Exiters

observablemissing

observablemissing

Type-3 Entrants

missing

observablemissing

missingIndependent variables Dependent variables

The sample selection problem does not always cause a biased estimator. Let yi T
 0  1  and x i 0ln i T ,1 ln i0 . Hereafter, “ ” denotes a transpose. The regression equationis rewritten as:
yi T


x i0

 iT 

We first consider the firms that are observed in year 0 (Type-1 and Type-2 firms in Table 1). For
these two types of firms, the independent variables x i0 are always observable. The problem isthat we cannot observe yi T for Type-2 firms because Type-2 firms exit from the market between
year 0 and year T .5
Suppose that the firm i’s survival in year T (s iT

1) depends on the productivity and other4 For more detail, see Heckman (1976).
5 If firm i exits from the market between year 0 and year T , 

iT it is not observable, and the growth rate of TFP, ln iT cannot be defined. This means that yiT is a missing variable.

4




firm characteristics in year 0, Z i0
si T1 ln i0  z 1i 0  z 2i 0    :1 if Z i 0   iT  0
 E  iT Z i0 0otherwise0 and N 0 1

iT

(3)

Assume that  i T  i T  is independent of Z i 0 and bivariate normal with zero means. This inturn implies thatE  yiT Z i0  i T 
x i0

  iT 

where  is some parameter that satisfies E  i T

iT 

 iT .6

If 

0, E  yiT Z i0  i T 

Z i0 andiT , E  yi T Z i 0  si T E  yi T Z i 0 E  yiT x i0 

 . Since si T is a function ofx i0

E  yiT Z i0  i T . Therefore, E  yi T Z i 0  si T 

OLS using only Type-1 firms yields a consistent estimator when 
In contrast, if 0.

0, we have, using iterated expectations,xi 0

E  yiT Z i0  si T 
where h  Z i 0  si T 

 . That is,
x i0


x i0

  E  iT Z i 0 si T   h  Z i0  siT (4)

E  iT Z i0  s iT . OLS using the observed data thus produces inconsistentestimates of .
It is, however, possible to estimate    consistently by a maximum likelihood (ML) method.

The log-likelihood function of the sample selection model for firm i, ln

ln

ln 

i

¼
Z i0
  yi T xi¼ 0 

1 2

 i , is  12 y x   ln 2 
iT

¼

i0

ln  Z i0  

2

if si T1

if si T0

where  is the standard cumulative normal distribution function. The key estimate(5)
isobtained from the ML estimate of the parameters of equation (5) using the data set including
both surviving (Type 1) firms and exiting (Type 2) firms.
So far, we have not considered the effect of entry. However, entrants (Type-3 firms in Table
1) are not likely to have biased effects on the speed-of-convergence equation. As explained before, exiting firms may cause a bias if we estimate equation (2) by OLS using only the observed
data (that is, surviving firms), because exiting firms’ dropping out of the observed data set islikely to be correlated to their productivity level. In the case of entries, we do not have such
6 The assumption that i T  iT  is bivariate normal means E iT iT   iT for some number  T . For moredetail, see Wooldridge (2002, p. 562).

5

correlation. In fact, Nishimura, Nakajima and Kiyota (forthcoming, Figure 2 and 3) find nosystematic relationship between new entries and productivity levels after entry: new entrants do
not always have significantly higher (or lower) productivity than existing firms. 7 If there is no
systematic relationship between entry and productivity after entry, or entry is randomly determined independently of subsequent development, then the above-mentioned ML method yields
a consistent estimator. More detailed explanation will be provided in the Appendix below.

2.3 Data
The micro database of Kigyou Katsudou Kihon Chousa Houkokusho (The Results of the Basic
Survey of Japanese Business Structure and Activities) prepared by METI (1996-2002)was used
for this study. This survey was first conducted in 1991, again in 1994, and annually thereafter.
The main purpose of the survey is to capture statistically the overall picture of Japanese corporate firms in light of their activity diversification, globalization, and strategies on R&D andIT.
One of the strengths of this survey is its sample coverage and information reliability. The
survey covers both manufacturing and non-manufacturing firms with more than 50 employees
and with capital of more than 30 million yen. 8 Industry data is available at a 3-digit level.
Another strength of this survey is that it is based on firm rather than establishment. Japanese
Census of Manufactures omits information about establishments not engaged in manufacturing
activities such as headquarters, sales blanches and R&D institutions. It is clear, that the simple
aggregation of manufacturing plants does not always depict the true picture of a “firm” unless
it is a single-plant firm. In that sense, our data captures the activity of firms more accurately
than studies which use data based only on the manufacturing plant census. A limitation of thesurvey is the lack of sufficiently-detailed information on financial and institutional features suchas keiretsuNOTE: This term needs to be defined if the audience may potentially be wider thanjust Japan.). Similarly, information on finance, location, and intermediate inputs is not detailed
enough to investigate these variables fully.
7 However, this result may be specific to Japanese firms in our data set, and may not be generalized. Aw etal. (2001, Table 5) found that new entrants were, on average, less productive than existing firms in Taiwanesemanufacturing.
8 Some industries such as finance, insurance, and software services are not included.

6

From this survey, we develop a longitudinal panel data set for the years from 1994 to 2000,
following procedures used by Nishimura et al. (forthcoming). 9 We dropped the firms from oursample set for which the firm-age (the year of the survey minus the year of establishment), total
wages, tangible assets, value-added (sales minus purchases), and/or the number of workers are
not positive and in cases with incomplete replies. However, such anomalous data are rather rare,
and thus the number of firms in our final data set exceeds 22,000 each year.

2.4 Productivity Measurement
To make comparisons of productivity across firms and time-series, we employ the multilateralindex method in computing TFP developed by Caves, Christensen and Diewert (1982) andextended by Good, Nadiri, Roeller and Sickles (1983). 10 The advantage of a multilateral index
is that we do not assume any specific production function, which is in line with the baselinemodel described in Section 2.1.
This multilateral index uses a hypothetical firm that has the arithmetic mean values of log
output, log input, and input cost shares over firms in each year. Each firm’s output and inputs aremeasured relative to this hypothetical firm. The hypothetical firms are chain-linked over time.
Hence, the index measures the TFP of each firm in year t relative to that of the hypothetical firmin year 0 (initial year).
Specifically, the TFP index for firm i in year t is defined as:
ln it



              tln Q itln Q tln Q

ln Q

ln X i j t

ln X j t

1

1

J

j 1
t

1
i j t2J1 j 1

 jt

1
j
2

j

1

ln X jln X j1(6)

9 Detailed description of our data set is found in Nishimura et al. (forthcoming) as well as that of methods used

to construct TFP measures.
10 There is an alternative method that is based on the econometric estimation of production functions, which
is proposed by Olley and Pakes (1996) and extended by Levinsohn and Petrin (2003). However, this frameworkhas to specify a production function, which is not consistent with our baseline model. Moreover, because of thelimited availability of intermediate inputs, their method was not feasible. Therefore, we employ a multilateralindex method in the present study.

7where ln Q it , ln X i j t , and i j t are the log output, log input of factor j , and the cost share of factor

j for firm i, respectively. ln Q t , ln X j t , and  j t are the same variables for the hypothetical firmin year t and are equal to the arithmetic mean of the corresponding variable over all firms inyear t.
The first term of the first line indicates the deviation of the firm i ’s output from the outputof the hypothetical firm in year t. The second term means the cumulative change in the outputof the hypothetical firm from year 0 to year t. The same operations are applied to each input jin the second and the third lines, weighted by the average of the cost shares.
Output is defined as value-added while inputs are capital and labor. As for other additional
data and their manipulation, we adopt the methodology described in Nishimura et al. (forthcoming).

3

Estimation Results

3.1 Sample Selection Biases Caused By Exits
Since we explicitly consider possible biases caused by exits, our baseline model consists of aspeed-of-convergence equation and a selection one. From equation (2), the speed-of-convergenceequation is specified as follows:ln i Twhere0

 1 ln i0  i T (7)ln iT indicates the TFP growth of firm i from year 0 to year T , i 0 represents theinitial level TFP, andi T represents error term.

11 In the estimation, we use

it instead of i t for

simplicity. This does not cause any problems, since the log form means that the estimatedusing i t is not different from

1 using it (it simply shifts

1

0 ).

The selection equation captures the effects of exiting decisions of exiting firms. Dunne,
Roberts and Samuelson (1989) find that plant size, age, and ownership type (single-plant firm or
multi-plant firm) are statistically significant determinants of plant growth and failure. Following
the findings of Dunne, Roberts, and Samuelson, we assume that exit depends on three factors:
firm age ( AG E), employment scale (L), and multi-plant dummy (D mul ti that takes value one
if a firm has multi-plant and zero for otherwise). In addition, we assume that natural selection
11 Although we focus on TFP, we obtained almost the same results for labor productivity.

8

mechanism works: firms with lower productivity exit from the market. Thus, the selectionequation for the exiting firms is represented as follows:
si T

multi
1 if 0  1 ln i0  2 ln AG E i0  3 ln L i0  4 Di0
 iT  00otherwise.

Table 2 reports the estimation results of the baseline model with and without selection equations. The results without the selection equation (Model 0) is generated by OLS while theresults with the selection equation (Model 1) is generated by ML estimation using equation (5)as explained in the previous section.
To obtain the speed-of-convergence, we first estimate
1 and :relationship between

1

1 , and then compute  using the1  1  T  T . Note that the baseline model without

the selection equation uses only Type-1 (surviving) firms so that we lose 8649 observations ofType-2 (exiting) firms.
Table 2: Baseline Model and Sample Selection Bias
Model 0Model 1

Selection equation

No

Yes

1

-0.071***-0.080***(0.002)(0.002)—-0.75***

(0.013)


8.8%

10.3%

N

10237

18886

—

313.39***LR test for H0 : 

0Note: Standard errors are in parenthesis. *** indicates significance level at 1%.

Two findings stand out from this table. Firstly, in both Models 0 and 1, we observe thestrong evidence of productivity convergence. However, the speed-of-convergence is different
between the two. The convergence speed is faster in Model 1 than in Model 0. Furthermore,
the coefficient of  is significantly negative. A log-likelihood ratio (LR) test for H 0 : 

0is rejected at the 1 percent level. This implies that there exists a statistically significant sample
9selection bias, causing about a 1.5 percentage point downward bias to . Thus, the results
clearly show the necessity to incorporate the selection equation in the analysis of firm-level
speed of productivity convergence.
Secondly, the speed of productivity convergence is significantly faster than the speed reported in the previous country-level studies. While, for instance, Dorwick and Nguyen (1989)
reported that the speed-of-convergence among countries was 2.5 percent annually, the resultof Model 1 shows that the speed of convergence is 10.3 percent. At first glance, this seems avery high rate, but it is not so high if one looks at its order of magnitude. Suppose that the
productivity level of firm i is 10 while that of the most productive firm is 100. If the speedof-convergence is 10.3 percent (i.e., 0103), it still takes about 23 years for firm i to catchup to the most productive firm. 12 Note that whether or not a firm can survive for more than
23 years is an important issue. Nishimura et al. (forthcoming, Table 3) confirmed that in Japan
about half of new firms exited from the market within five years. 13
Moreover, we should take account of the difference between firm-level analyses and countrylevel ones. Diffusion of technological knowledge can be much faster among firms within thesame country than among different countries because of so-called ”border effects.” The recent
studies on international economics emphasize the importance of ”border effects”: the tradeflows within the same country is much larger than the transaction between different countries.
For instance, McCallum (1995) found that trade flows among Canada’s different provinces were
22 times as large as trade between the Canadian provinces and U.S. states, despite that there
is virtually no trade barrier between these two countries. Engel and Rogers (1996) found thatprice adjustment suffered from ”border effects”, as well. They argue that national borders aswell as distance was an important impediment of price diffusion between different cities locatedin different countries. Similar arguments can be applied to the technology diffusion. Since wefocus on the diffusion within an industry in Japan, we expect that the speed of convergence ismuch faster than that of cross-country studies. 14
12 It takes more than 27 years to catch up to the most productive firm if the speed-of-convergence is estimated as
8.8 percent (Model 0).
13 This is not a Japan specific fact. In France, about 70 percent of new firms exited from the market within 10
years. See, Bellone, Musso and Quéré (2003) for more detail.
14 Another possibility is an effect of aggregation bias. The productivity growth of cross-country studies captures
not only productivity growth itself but also macroeconomic effects such as business cycles and sectoral shifts,
which might cause underestimation of the productivity growth.

103.2 Robustness Checks
The Choice of the Base Year
Our results may be sensitive to the choice of the base year. For instance, in his comments on
Bernard and Jones (1996), Sørensen (2001) finds that whether or not we observe convergence
depends crucially on the choice of the base year. To check the sensitivity of our results to the
choice of the base year, we changed the base year from 1994 to 1995, examined the productivity
growth between 1994 and 2000, and re-estimated the baseline model.
Table 3: Robustness Check: Base Year and ThresholdL  55

Base year = 1995
Model 0Model 1Model 1

Selection equation

No

Yes

Yes

1

-0.073***-0.081***-0.079***(0.002)(0.002)(0.002)—-0.713***-0.76***(0.014)(0.013)




8.7%

9.9%

10.2%

N

11449

19200

18235

—

230.87***321.80***LR test for H0 : 

0Note: Standard errors are in parenthesis. *** indicates significance level at 1%.

Table 3 presents the estimation resultsof changing the base year from 1994 to 1995. The
results indicate that the speed-of-convergence is not very sensitive to the choice of the baseyear. The estimated speed-of-convergence (9.9 percent) is almost the same as the speed-ofconvergence obatained in the baseline model (10.3 percent). Moreover, the coefficient of  issignificantly negative and a LR test for H0 : 

0 is rejected at a 1 percent level. Thus, ourresult is robust for the choice to base year.
Table 3 presents the estimation resultsof changing the base year from 1994 to 1995. The
results indicate that the speed-of-convergence might be sensitive to the choice of the base year,
as is often observed in the literature. However, the result of significant selection bias still holds
11true. Even after we change the base year, the coefficient of  is significantly negative and a
LR test for H0 : 

0 is rejected at a 1 percent level. Moreover, the estimated speed-of-

convergence, , is faster in Model 1 than in Model 0. Thus, although the speed-of-convergencemight depend on the base year, the existence of the downward bias to , due to selection bias,
does not depend on the choice of base year.
ThresholdAs indicated before, the survey covers both manufacturing and non-manufacturing firms withmore than 50 employees.15 One may be concerned with this truncation based on the thresholdof 50 workers. In our data, firms with less than 50 workers are not covered in the survey, andthus a firm whose employment is reduced below this level is regarded as an exiting firm.
To check the sensitivity of our results with respect to this particular threshold of 50 workers,
we re-estimated the baseline model for firms with more than 55 workers. The last column inTable 3 reports our estimation results. Despite the fact that 651 firms are eliminated from oursample, the speed-of-convergence is almost the same as the baseline model. Thus, our results
are not sensitive to the threshold of truncation.
Endogeneity
Finally, one may raise the issue of endogeneity: ln i 0 andi T in the baseline model (7) might

be correlated. To examine possible effects of this endogeneity, we applied instrumental variable(IV) methods to the speed-of-convergence equation (7).
In obtaining IV estimators, we employed Heckman’s two-step estimation procedure (Heckit)
rather than ML. In Section 3, we have used the ML method since this one-step procedure is generally more efficient than the two-step method of so-called Heckit estimation. 16 However, here
we use the Heckit framework since it provides a straightforward extension to the case of endogeneity, which is unfortunately not the case in the ML method.
We first estimated the Mills ratio using probit model and the Mills ratio is used as an additional variable to estimate the speed-of-convergence equation. Instruments utilized are industry
15 There is also a truncation based on the amount of paid capital. However, since paid capital is usually not agood indicator of firm size in practice, this truncation is considered not as serious as the truncation based on thenumber of employees.
16 See Johnston and DiNardo (1997, p. 450) and Davidson and MacKinnon (1993, p. 545).

12

average capital stocks excluding firm i , modified industry average employment excluding firm i,
returns-on-assets, and those deemed foreign-ownership dummy firms. Industry average capital
excluding firm i ( K i t ) and industry average labor excluding firm i ( L it ) are defined as follows:
K it

1

N 1

N 1
j 1 j i

K j t  Ki t

and L it

N 1

1

N 1

j 1 j i

L j t  L itwhere N is the number of firms in an industry. In computing these industry averages of capitaland labor, a firm’s own capital and labor are subtracted to remove endogenous factors.
Table 4 presents the estimation results of Heckit and IV estimators. It is remarkable to notethat the results from IV, taking account of Endogeneity, are almost the same as the results from

Heckit ignoring endogeneity. This in turn implies that possible endogeneity between ln i0 andi T does not lead to a significant bias, if any, in the speed-of-convergence estimation. Thus, wehave ignored endogeneity as a problem in this paper.
Finally, the coefficient of

1 from Heckit is smaller than the coefficient from ML in Table 2

reflecting the difference in estimation methods. In the remaining part of this paper we used ML
estimation using (5) as our baseline model since the one-step ML approach is more efficientthan the two-step Heckit approach.
Table 4: Robustness Check: Endogeneity
Model 1 Model 1
Selection equation

Yes

Yes

Estimation

HeckitIV-0.075-0.076(0.002)(0.006)-0.039-0.040(0.005)(0.007)



9.5%

9.6%

N

18886

18886

1

Mills ratio

Notes:
1 Standard errors are in parentheses.
2 Heckit: Heckman’s two-step estimation method is used forthe estimation.
3 IV: Instrumental variable method is used for the estimation.
4 For the IV results, standard errors are not adjusted.

13

3.3 Difference in Productivity Convergence across Industries
To examine the difference in the speed-of-convergence across industries, we include industry
dummies to the baseline model for both constants and initial TFP levels. Thus, constants andinitial TFP levels are now represented as:  1 D1       j D j0and  1 D1 ln i 0       j D j ln i 0

1 ln i0where D j is a dummy variable that takes the value one if firm i belongs to industry j . The
speed-of-convergence of industry j ,  j , is represented as:j T 1  1    

 
1

T

j

1

if  j is statistically significant at 10% level;otherwise.

Table 5 reports the number of industries by the magnitude of the speed-of-convergence,
. Out of 70 industries, nearly two-thirds of the industries report less than 15 percent and 7

industries report more than 20 percent. Note that firms in manufacturing present a faster rate ofconvergence than firms in non-manufacturing. Similarly, firms in IT industries tend to converge
faster than firms in non-IT industries.
Table 5: Distribution of the Speed-of-convergence (the number of industries)
Speed-of-convergence ( j ) based on Model 1
 3%

 5%

 10%

 15%

 20%

20% 

All industry

2

32

1

10

18

7

Manufacturing

1

11

0

9

17

3

Non-manufacturing

1

21

1

1

1

4

IT industry

0

1

0

2

3

1

Non-IT industry

2

31

1

8

15

6

14

4

Discussion

4.1 Importance of Technology Diffusion
We have confirmed strong evidence for productivity convergence among Japanese firms. But
why is productivity convergence important? One reason may be that technology diffusion behind productivity convergence expands opportunities for secondary firms to catch up to the leading firm. Suppose that there was no technology diffusion. Without the diffusion, the secondary
firms could not catch up to the leading firm without conducting their own R&D investment
or purchasing technology through patents, which is very costly for new entrants and existingsmall- and medium-sized firms.
The same argument can be applied to the difference between developed and developing
countries. Without technology diffusion, developing countries can catch up to developed countries only when they can afford to innovate or purchase technologies. This is also pointed out
by Helpman (1993). His theoretical analysis shows that to tighten intellectual property rights
benefit developed countries and hurt developing countries under some rates of imitation.
We should note, however, that instant technology diffusion causes yet a different problem.
If technology diffuse too easily, no firms would have an incentive to conduct R&D investment.
However, our results clearly indicate technology diffusion is not instantaneous but rather takes
a long time. Thus, a technological advantage of a leading firm can still exist for a long time,
which gives firms enough incentives to create innovative technologies. 17

4.2 Difference in Selection Biases among Industries
Section 3.1 has shown that estimation without the selection equation causes a 1.5 percent point
downward bias in the speed of convergence. We still have similar sample selection biases when
we allow for different speeds of convergence in different industries.
Table 6 reports OLS regression results ignoring selection biases, that is, OLS without selection equations. The speed-of-convergence is much slower than the results presented in Table
5. Out of 70 industries, more than three-fourth of the industries report less than 15 percent andonly two industries report more than 20 percent. The results clearly indicate that the estima17 In a companion paper (Nishimura et al., 2005), we examine the difference of the effects between diffusion andinnovation in more detail.

15

tion of productivity convergence without the selection equation underestimates the speed-ofconvergence.
Table 6: Distribution of the Speed-of-convergence without Selection Equation
Speed-of-convergence ( j ) based on Model 1
 3%

 5%

 10%

 15%

 20%

20% 

With selection equation

2

32

1

10

18

7

Without selection equation

1

30

10

20

8

1

4.3 Determinants of Industry Differences: Manufacturing, IT, and Overall Growth
Tables 5 and 6 indicate that there exist large sectoral differences in the speed-of-convergence.
There are at least three reasons. Firstly, the speed-of-convergence is different between manufacturing and non-manufacturing. Previous firm- or plant-level studies mainly focused on manufacturing firms (plants) and they did not give us much information about non-manufacturingsectors. Table 5 clearly shows a large difference between manufacturing and non-manufacturingfirms.
Secondly, the difference between IT and non-IT industries matters. As we confirmed inTable 5, IT industry firms tend to catch up rapidly compared with non-IT industry firms. The
existence of sectoral difference may be partly attributed to IT effects.
Finally, the speed-of-convergence is different between growing and declining industries.
Table 7 presents the distribution of the speed-of-convergence, by industry productivity growth.
Industry productivity growth is defined as the average of the productivity growth of firms in anindustry. The table classifies industries into three groups: (1) of a negative productivity growthrate, (2) of a less than overall average growth rate (2.4 percent), and (3) of a more than or equal
to overall average growth.
Table 7 indicates that the very rapid convergence is found in two polar cases: declining
industries and rapidly-growing industries. In the declining industries having very rapid convergence, the observed high rate of convergence might be due to a “productivity collapse” of16

Table 7: Distribution of the Speed-of-convergence, by the Industry Productivity Growth
Speed-of-convergence ( j ) based on Model 1
Industry productivity growth

 3%

 5%

 10%

 15%

 20%

20% 

 0 % (declining industries)

1

5

0

2

1

3

 2.4% (steadily growing industries)

1

18

1

5

11

0

0

9

0

3

6

4

 2.4 % (rapidly growing industries)

leading firms rather than true catch-up of secondary firms. This is an interesting possibility thatwill be a topic of future research.
In the modest-rate range, the relatively fast productivity catch-up is mainly observed in
the growing industries; while the relatively slow catch-up occurred in the steadily growing
industries. To sum up, these results suggest that at least a part of the sectoral difference can be
explained by the difference between growing and declining industries.

5

Concluding Remarks

This paper has examined the growth of productivity at the firm level, especially focusing on
the effects of convergence. Our findings are summarized as follows. Firstly, the productivity
convergence among firms exists not only in manufacturing but also in non-manufacturing industries. In addition, the speed-of-convergence is faster than the speed observed in the previous
national- or industry-level studies, which indicate an annual average rate of 10.3 percent.
Secondly, analysis without considering the effects of exits causes a statistically significant
sample selection bias in the speed-of-convergence estimation. We have used sample selection
models to correct the bias and have found a 1.5 percent point downward bias in the speed-ofconvergence in the analysis without the selection equation.
Finally, we have found a wide difference in the speed of productivity convergence amongindustries. IT industries tend to have faster rates of productivity convergence than non-IT industries. Similarly, manufacturing industries tend to have faster rates of convergence than nonmanufacturing industries.
17

Two policy implications may be suggested from our analysis. Firstly, tightening intellectual
property rights should be discussed more carefully. While the intellectual property rights could
promote innovation (through R&D), the lack of technology diffusion prevents secondary firms
from catching up to a leading firm. Since secondary firms are likely to be new entrants and/or
small- and medium-sized firms, strong protection on intellectual property could be harmful for
their growth.
Secondly, policy makers should recognize that not only innovation but also diffusion is an
important source of productivity growth. The promotion of innovation is an important policy
but it is important to also address a policy toward technology diffusion so that firms don not haveto always invent everything by themselves. The combination of diffusion as well as innovation
enables us to use limited resources more effectively.

18

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20

Appendix
We have assumed in the text that there is no systematic relationship between entry decision andproductivity after entry, or in other words, that entry is randomly determined independently ofvariables that determine productivity after entry. Under this assumption, the ML method yields
a consistent estimator.
To see this, suppose that, in addition to Type-1 and Type-2 firms, there are Type-3 firms(entrants after period 0. Assume that the firm i ’s existence in year 0 depends on the productivityand other firm characteristics in year 0, Z i0
i01 ln i 0  z 1i0  z 2i 0 

1 if Z i 0   i0  0 E  i0 Z i 0 0otherwise

Type-1 and Type-2 firms have i0   :

0 and

i0

 N 0 1

1, while Type-3 firms have i 0

0. Assume that (i) iT  i T  is independent of Z i 0 and bivariate normal with zero means as before and assume

further that (ii) there is no systematic relationship between entry decision and productivity after
entry, which is formally represented as an assumption thati0 is independent ofiT  andiT

as well as Z i0 . This implies
E si T Z i 0  i 0 E  Z i 0  

iT Z i 0  i0 E  Z i 0  

iT Z i0 

Z i 0 

so that the ML method applied to estimate siT using only Type-1 and Type-2 firms yields a
consistent estimator.
Similarly, sincei0 has no correlation withE  yiT Z i0  i T  i 0 
where T is such that E  iT
E  yiT Z i0  i T iT E xi 0

iT andi T , we have iT Z i0  i T  i0 x i0  iT  iT as before. This in turn implies that E  yi T Z i 0  i T  i 0 E  yiT Z i 0  si T , which is equivalent to equation (4). Thus, the ML method

applied to estimate yiT using only Type-1 and Type-2 firms yields a consistent estimator.
This property is particularly important in our estimation, since crucial information about
Type-3 firms in the estimating equation (2) is missing as exemplified in Table 1.

21