DPRIETI Discussion Paper Series 11-E-047

Evidence of a Growing Inequality in Work Timing Usinga Japanese Time-Use Survey
KURODA Sachiko
Waseda University

YAMAMOTO Isamu
Keio University

The Research Institute of Economy, Trade and Industry

http://www.rieti.go.jp/en/

RIETI Discussion Paper Series 11-E-047
April 2011

Evidence of a Growing Inequality in Work Timing
Using a Japanese Time-Use Survey
KURODA Sachiko (Waseda University)a

YAMAMOTO Isamu (Keio University)b

Abstract

Using data from a Japanese time use survey, we show a noteworthy increase in the share of
employees working unusual hours (late night and early morning) over a period of a decade since themid 1990s. When controlling for changes in hours worked, however, we find that the notable
increase in the fraction of people working unusual hours was for low-income nonregular employees(part time, temporary and contract workers), while relatively higher-income regular employees’
work timing remains stable. These observations imply that there is a trend of diversification of work
timing in Japan between regular and nonregular employees. A possible explanation is that theincrease in the average hours worked per weekday by regular employees, possibly because of the
spread of the five-day workweek since the 1990s, increased the demand for services and goods
during unusual hours, as they returned home. An Oaxaca–Blinder type decomposition suggests thatsuch an increase in the average hours worked by regular employees explains partially the rise in theemployment rate of nonregular employees at unusual times. We also suggest that the negative
income effect induced low-wage nonregular employees to take jobs at night to earn a wage
premium.

RIETI Discussion Papers Series aims at widely disseminating research results in the form of professional
papers, thereby stimulating lively discussion. The views expressed in the papers are solely those of theauthor(s), and do not represent those of the Research Institute of Economy, Trade and Industry.



The micro data used in this paper are data from the Survey of Time use and Leisure Activities (Statistics Bureau, Ministryof Internal Affairs and Communications; MIAC). The authors would like to thank the MIAC for providing these data. The
authors would like to thank Ryo Kambayashi, Akira Kawaguchi, Daiji Kawaguchi, Yuichiro Mizumachi, Masayuki
Morikawa, Fumio Ohtake, Yoichiro Shimada, Kotaro Tsuru, Ryuhei Wakasugi, Kazuo Yamaguchi and participants at the
Study Group for Labor Market Institution Reform in Japan at REITI, the 31th IATUR conference, and the Japanese
Economic Association Annual Meeting for their valuable comments. The remaining errors are solely of our own.
ab

Waseda University, 1-6-1 Nishiwaseda Shinjyuku-ku Tokyo 169-8050, Japan (e-mail:s-kuroda@waseda.jp)
Keio University, 2-15-45 Mita Minato-ku Tokyo 108-8345, Japan (e-mail:yamamoto@fbc.keio.ac.jp)

I. Introduction
The 24-hour lifestyle has become deeply rooted in some societies around theworld. Japan is a prime example. Nowadays, many businesses such as evening andweekend banking, 24-hour customer services, convenience stores, and all-night movie
theatres operate outside standard hours in Japan. The 24/7 convenience stores, forexample, have increased tremendously in number within Japan in recent decades.
According to a report issued by the Japan Franchise Association, there were 6308
convenience store outlets in Japan in 1983, and rapid growth since then has increased
the total to 42 629 stores in 2009.1 In Metro Tokyo, there are some areas where it is
impossible to walk 30–40 meters without passing a convenience store. From theconsumer’s point of view, such 24-hour businesses offer a high degree of convenienceespecially for two-income families with little time to spare during the workday.
However, longer and nonstandard hours in such businesses are required by the workers
who work at those hours, which reflects the main characteristics of the service:simultaneity. This implies that the number of people who work at unusual hours is also
growing.
There are legitimate questions, however, as to what extent people actually work
unusual hours, how far has employment shifted toward unusual hours, and also, themain reason behind the expansion in operating hours. Is it globalization, the advent oftechnology such as mobile phones and the internet, changes in open-hour legislation orlabor market regulation, or a huge negative demand shock that hit the economy from theearly 1990s changed Japanese lifestyles? Detailed answers to these questions remain
elusive. This paper uses a Japanese time use survey to examine how the timing of workin Japan has changed since the 1990s and attempts to identify the driving forces behindthe 24-hour society.

1

Among them, 7-eleven leads the market with 12 743 stores (as of March 2010) in Japan, comparedwith only 6547 stores in the US.

1

There is little research that focuses on the timing aspect.2 The exceptions are
pioneering studies by Hamermesh (1999a, b, 2002) that focused on US workers. Using
the Current Population Survey (CPS) for 1973–1991, Hamermesh (1999a) found thatthe share of US workers working late-night hours declined gradually over time.3 Given
the anecdotal evidence above, Japan seems to be heading in the opposite direction fromthat of the US. This paper uses detailed Japanese time use micro data to assess
empirically whether this conjecture is correct. Specifically, the data we use are from theSurvey on Time use and Leisure Activities, a time use survey conducted by the Japanese
government’s Statistics Bureau within the Ministry of Internal Affairs andCommunications (MIAC) since 1976. Respondents to the survey, nearly 200,000
Japanese citizens, annotate their activities in 15-minute increments over two
consecutive 24-hour periods. This paper uses data from the 1996, 2001, and 2006
surveys.
The results of this paper are as follows. First, we show that Japan experienced anoteworthy increase in the share of workers working at unusual times (late night andearly morning) over the period of a decade from the mid 1990s. Second, whencontrolling for changes in hours worked, however, we found that a notable increase in
the fraction of people at work at such unusual times was evident for low-income
nonregular employees (part time, temporary and contract workers) while relatively
higher-income regular employees’ work timing remains stable. These observations
imply that there is a trend of diversification of work timing in Japan between regularand nonregular employees. Third, the increase in the average hours worked per weekday
by regular employees, possibly because of the spread of the five-day workweek since2

Much of the literature in economics that makes use of time use surveys is based on analysis thatmeasures an aggregate of work time and leisure time. Sociology, however, has a longer history ofliterature analyzing activities by time of the day. For example, Szalai (1972) showed that in the US,
activities for each time slot differ depending on the city, while Presser (1987) analyzed the timing of
the work of spouses. The survey by Gershuny and Sullivan (1996) is also of interest.
3

The series of papers by Hamermesh do not use time use surveys but rather information on theusual start and end times of working hours extracted from questions in the CPS.

2

the 1990s, increased services and goods demands at later hours as workers returned
home. An Oaxaca–Blinder type decomposition suggests that such an increase in the
average hours worked by regular employees explains partially the rise in theemployment rate of nonregular employees at unusual times. We also suggest that thenegative income effect induced low-wage nonregular employees to take jobs at night toearn a wage premium.
This paper is organized as follows. In Section II, we explain the theoreticalunderpinnings of our analysis, and in Section III, we provide an overview of our data. In
Section IV, we examine how the timing of work in Japan has changed over the period ofa decade from the mid 1990s. In Section V, we further analyze the data to identify themain factors that lead people to work at unusual hours. We end with our conclusions in
Section VI.
II. Theoretical Underpinnings
Following Winston (1982) and Hamermesh (1999a), we assume that individual ichooses daily the timing of work so as to maximize the following utility function
Vi  U it (1  Lit , Cit ),subject to  ( wit Lit  Cit )  0,t  1,,24(1)

where Lit is an index function that takes the value 1 if individual i is working at time t(an hour block of time within the 24-hour day), and 0 otherwise; wit is the wage rate if
individual i is working at time t, Cit is consumption at time t, and the consumer goods
price is 1 for simplicity. We assume here that leisure and consumption areintertemporally additively separable, and thus that leisure and consumption are
separable at each t. Because we are considering a utility function for one day only, we
do not use a discount rate. We also assume that fatigue does not impact the choice
between consumption and leisure for individual i at time t, because we are addressing
decisions for each time block. When the following equation is satisfied, individual iworks at time t.

(U it / Lit ) /(U it / Cit )  wit(2)
3

The above equation is based on the same logic as the corner solution in astandard labor supply model for an individual’s decision on whether to participate in thelabor market (whether to work or not work), with the only difference being that thedecision is on whether to work at time t. The left-hand-side term in equation (2) is thereservation wage of individual i at time t. Just as each individual has a different
reservation wage, each time t has a different reservation wage, even for the same
individual. In other words, the perceived disutility of an individual will differ dependingon the work timing.
We next consider the demand side. We assume that the firm engages in
profitable production activity during various blocks of time throughout the day. The
profit function of firm j is given by j  j (a j1 N 1 ,  , a j 24 N 24 ; w)(3)

where Nt is the number of workers at time t, ajt is labor’s contribution to firm j’s profit attime t, and w is the average wage of workers employed by firm j.
The equilibrium is shown by the standard implicit contract model of Rosen(1986). That is, the labor demanded by firm j at time t, holding other conditions
constant, is supplied by the worker, out of those with the lowest reservation wages attime t, with the highest ajt.
The labor market’s wage premium  t at time t is determined by the distributionof workers’ reservation wages at time t and by the distribution of ajt. The wage at each t
is given by wit  wi (1   t ) . Like Hamermesh (1999a), we assume that there are time
periods t where firms cannot fully meet their demand for labor when  t = 0. In otherwords, there are time periods that are undesirable as a time to work for a large numberof workers although firms can profit from operating at those times, and the wage
premium (  t '  0 ) then serves to motivate workers to supply labor at those times.4
4Here, we assume that  t is determined by the labor market, although the overtime premium thatapplies to hours worked beyond the legal workweek is actually prescribed by law in many countries,
and Japan is no exception to this. According to Japan’s Labor Standards Act, legal work hours areeight hours per day and 40 hours per week, and firms must pay an overtime premium of at least4Holding other conditions constant, it is lower-income workers who will be motivated bya wage premium to work at times when the marginal disutility of labor is high, i.e., atundesirable work times.
Using this model, Hamermesh (1999a) made the following three assumptions:(1) workers’ preferences do not change over time; (2) the higher the proportion ofworkers with relatively low human capital endowment working at a given time, the lessdesirable is that time for workers as a time to work; and (3) technical innovations have auniform impact on the average productivity of workers across different time blocks, andimpact the productivity of workers in various time blocks. Under these assumptions,when average real wages increase (decrease) within an economy, the share of workers
who work at undesirable times should decrease (increase) because of the income effect.
Moreover, when income inequality increases, higher income workers take work at
desirable times while low-income workers are likely to take work at undesirable times(to earn a wage premium), and this would lead to a widening discrepancy in work
timing across income levels. Hamermesh (1999a) found a decline in the number ofworkers who worked during the undesirable times with a high marginal disutility oflabor,5 along with an increase in average real wages and also suggested that this trend isstronger for individuals with higher incomes, consequently suggesting a widening
discrepancy in the timing of work based on income level.

25 % for any hours that exceed this. If this overtime work is done during late-night hours (defined asfrom 10:00 pm to 5:00 am), the required premium is at least 50 % (a 25 % premium for late-nightwork and a 25 % premium for overtime work). Kawaguchi, Naito, and Yokoyama (2009) showedthat nearly all of the wage premia actually paid in Japan were above the 25 % level. It is unclear
whether the legally prescribed wage premium is higher than that determined by the labor market (i.e.,than the potential wage premium).
5

Using the CPS and data from the FBI crime report on the number of murders by region,

Hamermesh (1999b) showed that the fraction of people at work late at night was lower for regionswith higher murder rates. This could be interpreted as corroboration that late-night work has a highmarginal disutility of labor. Additional trials in Hamermesh (2002), which extended the CPS data set
to 1997, also showed a decline in late-night work by US males.

5This paper focuses on the growing number of nonregular employees withrelatively lower wages in the Japanese labor market. We here define nonregular
employees as nonstandard workers, consisting of part time, temporary and contract
workers. From the early 1990s, Japan experienced a long-term economic slump, Japan’sso-called ‘lost decade and a half’. During this period, average real hourly wages havedeclined. Moreover, many firms reduced personnel expenses by cutting back in hiring
regular employees representing high fixed costs and hiring instead inexpensive
nonregular employees with relatively low skills. This practice was particularly common
for new hires, especially among new graduates who entered the labor market during theprolonged recession looking for regular full-time jobs. Accordingly, the share ofnonregular male employees has expanded significantly; from 8.9 % in 1996 to 18.59 %in 2006 (figures are from the Labor Force Survey and the Special Survey of the Labour
Force Survey, MIAC). For those aged under 34, the share of nonregular male employees
has grown from 10.1 % to 22.1 % during the same period, partly as a consequence of
having no choice but to be hired as a nonregular employee, or otherwise be
unemployed.
Under these circumstances, we expect more nonregular workers have taken
late-night work because of negative income effects. This is because, in general, workers
who face real wage declines would either work longer hours or take jobs at undesirable
times with a wage premium (or both) in order to compensate for the (potential) income
losses. We expect this may be more likely to occur for nonregular employees, because
the average hourly wage of nonregular employees is roughly two-thirds of that ofregular employees and the wage gap has been widening during this period (see Ohta
2005 for example) 6 . For nonregular employees who desire to work as a regular
employee, the current wages must be much lower than their desirable level, whichconsequently would induce a negative income effect. We take a closer look at thisbelow, by separating our samples into regular and nonregular employees.
6

Since there is no ‘equal pay for equal job’ type regulation in Japan, the average hourly wage ofnonregular employees is considerably lower than that of regular employees.

6III. Data
Our data come from the Survey on Time use and Leisure Activities (STULA), a
Japanese time use survey conducted by MIAC. STULA has been conducted every five
years since 1976, in the year following the Population Census. It is a large-scale surveythat first selects approximately 6000 survey districts from those established for the
Population Census, out of which it selects approximately 70 000 to 100 000 households,
in which live about 200 000 to 270 000 household members who are at least 10 years
old. The sample size (number of households and household members) varies eachsurvey year. The survey is based on answers from individuals regarding a consecutive
two-day period that is set for each survey district, and thus the sample size isapproximately twice the number of household members surveyed. The survey covers
every day of the week during a nine-day period from late September to early October.
We use the latest three surveys conducted in 1996, 2001, and 2006.
The survey respondents recorded their activities, chosen from a list of 20
possibilities, for each 15-minute increment within the 24-hour day. Our measure ofhours worked corresponds to the category called work in STULA. The respondents are
given a detailed definition of work, which states that ‘work includes various types ofwork, such as regular work, preparatory work and clean-up work, overtime, take-home
work, part-time work, moonlighting, and help with the family business’. It does notinclude time taken for rest breaks or meals during the workday. In addition to theiractivities, respondents are asked other basic information such as age, level of education,
marital status, whether they have children, number of persons in the household,household annual income, number of employees in the workplace, and length of usual
workweek. For more information about STULA, see Kuroda (2010).
We limit our analysis to male employees, and exclude the self-employed.7 The
basic statistics for our sample are shown in Table 1.8

7Students are included in our samples. Because they are small in number, however, excluding themwould not change the findings of our paper.

7

IV. Timing of Work
Changes from 1996 to 2006
Figs 1(1) and 1(2) show the employment rate during the day, that is, the fractionof people at work (employment rate) for each 15-minute intervals in a 24-hour day in1996 and 2006 using weekday samples (from Monday through Friday). First, looking at
Fig. 1(1) for regular employees, the overall shape of the distribution shows theemployment rate is over 50 % from 8:00 am to 9:00 am, and rises to close to 85 % after
9:00 am. It then drops to about 30 % around noon (lunchtime), returns to nearly 85 %from 1:00 pm to 5:00 pm, and then gradually declines from the early evening. The slightdeclines around 10:00 am and 3:00 pm can probably be attributed to the large number of
employees who take a break around those times. Looking next at Fig. 1(2) for
nonregular employees, we find the overall shape of the distribution relatively similar tothat of regular employees. That is, the employment rate rises from morning and reaches
its peak before and after noon, and gradually declines from the early evening.
Changes in these employment rates by time of day also show a common trend
for both regular and nonregular employees. That is, the tails at both ends of the
distribution became fatter, as the employment rate from 6:00 pm until 6:00 am (evening,late night, and early morning) increase. This is the opposite of findings in Hamermesh(1999a), which show a decline in nighttime work in the US.
The extent of the change in the employment rates, however, is quite different
between regular and nonregular employees. For example, the fraction of people working
at midnight in 1996 was not very different between the two groups. In 2006, however,
the employment rate seems to be double for nonregular employees at midnight, whilethat of regular employees remains stable. A significant rise in employment rates during
unusual periods (especially from about 10:00 pm to 5:00 am) can be observed for thenonregular employees. Another notable feature that can be seen only for nonregular

8

Unless noted otherwise, all analysis from this point forward is based on calculations using weights

provided by the Statistics Bureau of the MIAC.

I

8employees is that the employment rates during daytime show a significant drop overthis decade.
To examine this more closely, Table 2 shows the employment rate for seventimes of the day in 1996, 2001, and 2006 for weekdays. The employment rate at 11:00
am declined 5.6 % for nonregular employees while the rate has not changed for regular
employees as seen in Fig. 1. Furthermore, the fraction of employees working at
midnight, very early morning (3:00 am and 5:00 am), evening (7:00 pm), and late night(10:00 pm to midnight) has risen over the 10-year period. In particular, those of
nonregular employees have shown substantial increases during late night and very earlymorning hours. The results of significance tests for differences between 1996 and 2006
are reported at the bottom of each row.
It is striking that the employment rate at 7:00 pm on weekdays has risen to35.6 % for regular employees in 2006. This implies that more than one-third of regularmale employees are working at 7:00 pm. It is important to note that Japan’s Labor
Standards Act was amended in 1988, and the legal workweek was shortened from 48
hours to 40 hours. This has led to wider adoption of the five-day workweek since the1990s, which has resulted in a substantial change in the allocation of work hours
between weekdays and weekends (Saturday). Kuroda (2010) found that the ratio offull-time workers working more than 10 hours per day during weekdays has increased
from 35 % in 1996 to 43 % in 2006, because many people have begun to squeeze theirwork into five days. The increasing fraction of people working at night may havesomething to do with the longer work hours within the day. Table 3 shows that the
average hours worked per day during weekdays has increased for regular employees
while that of Saturday has decreased from 1996 to 2006. Specifically, the hours worked
per weekday from Monday through Friday averaged 8.86 hours for regular employees
in 1996, but increased to 9.21 hours in 2006. In contrast, there was a decline in thehours worked on Saturday, because of the fact that more people are taking Saturday off.
Thus, one may argue that the observed change in the timing of work for regular9employees was because of the change in the number of hours worked resulting from
regulatory changes (and/or business cycles).
For nonregular employees, however, there is no trend in average work hours
except that a slight decline can be seen for Saturdays. As stated in the previous section,
workers who faced real wage declines are likely either to work longer hours or to takework at undesirable times with a wage premium to compensate for the income losses. It
seems, however, that the former effect cannot be seen for nonregular employees on
average. We further consider this point below. However, we first check to see if there
were any changes in the timing of work even after adjusting for the number of hours
worked in the next section.

Adjustment of the number of hours worked
We conduct an Oaxaca–Blinder type decomposition to compare the employment
rates between 1996 and 2006, which are adjusted for the difference in hours worked.
We first estimate the following probit modelPr( Lits )   ts H is  eits , t  1, ...., 24 , s  1996, 2006

(4)

where Lits indicates whether individual i is working at time t, taking a value of 1 forworking and 0 for not working, s is the survey year, His is the daily work hours ofindividual i in year s, and eits is the error term. Then, we decompose the changes in theemployment rate from 1996 to 2006 into explained and unexplained factors based on
Fairlie (2005) and Jahn (2008), as in equation (5). The explained factor Fe represents thechanges in the employment rate brought about by changes in the number of hours
worked. The unexplained factor Fu represents the rest of the factors that increased theemployment rate even when hours worked were fixed at the 1996 level.

Lt ,06  Lt ,96  F e ( H 06 , H 96 | ˆ t ,06 )  F u (ˆ t ,06 , ˆ t ,96 | H 96 )(5)

Table 4 shows employment rates by time after adjusting for hours worked. The
table suggests that most of the changes in the fraction of regular employees in each time
period can be explained by the ‘explained factor’, that is, the changes in the number of10

working hours. As for nonregular employees, however, the changes in the fraction ineach time period cannot be explained by the changes in the number of work hours. Thisimplies that the cause of the increasing fraction of nonregular employees working at
unusual times is due to other factors besides the changes in the length of hours worked.
In the next section, we focus on nonregular employees and look for the causes of theincreased fraction of employment at unusual hours.
V. Causes of Increased Employment Rates at Unusual Hours
Demographic change and possible causes
In addition to the number of working hours, the change in the timing of work
could also be caused by other factors, such as demographic changes in which people
marry later in life and have fewer children (which leads to an ageing society), orchanges in the occupational mix resulting from growth in the service industry. For
example, if there were a tendency for single workers to work late-night hours andelderly workers to work early-morning hours, the demographic changes associated withpopulation ageing and marrying later in life could possibly cause the late night andearly-morning employment rates to increase, even without any change in individuals’
lifestyles. It is also conceivable that an increase in the crime rate could necessitate morelate-night workers such as security guards, thereby raising the late-night employment
rate. We therefore check below to see if the trends seen in the previous section still holdeven after holding such changes constant.
We follow the same method taken in the previous section. Here, we modify
equation (4) as follows
Pr( Lits )   ts' X is  eits , t  1, ...., 24 , s  1996, 2006

(6)

where Xis is a set of variables that affect the employment decision of individual i at timet, and is is its coefficient vector. The variables we include in Xis are hours of work perday, age, education (university graduates = 1), marital status (married = 1), having achild less than six years old (having child = 1), and occupations (professional and11technical, managerial, sales, and blue collar; base = clerical). Because STULA does notcontain industry information, we also add the share of the service industry by prefecture
calculated from the Basic Survey on Wage Structure (Ministry of Health, Labour andWelfare) in order to control for structural changes in industries. STULA has information
on residential location by prefecture level; thus, we are able to match the data for eachsample.
Besides controlling for demographic and compositional changes, we add threevariables into Xis to identify the causes of the increased fraction of employment at
unusual hours: (a) the average number of hours worked by regular employees byprefecture, (b) the percentage of people who shop outside the hours of 8:00 am to 8:00
pm by prefecture, and (c) the male unemployment rate by region.
The average number of hours worked by regular employees is included in orderto capture long-working regular employees’ demand for services and goods on their
way home. As explained in the previous section, the average hours worked per weekday
by regular employees has increased in these years, possibly as a result of the spread of
the five-day workweek. This might have delayed the timing of leaving office on
weekdays, which implies that there should be plenty of demand for services and goods
at later hours, such as trains, buses, taxies, convenience stores, bars, restaurants, fast
food shops, and coffee shops. To motivate enough nonregular employees to work at
those times and meet this demand, firms would need to raise the late-night wage
premium.
Second, the percentage of people who shop outside the hours of 8:00 am to 8:00
pm is included to control for the effect of the open-hour legislation for large stores that
was abolished in 2000. Before 2000, large stores of more than 500 square meters were
under stringent control over opening hours by the Japanese government in order toprotect local small shops, and thus large stores were unable to operate after 8:00 pm.
After 2000, the legislation was deregulated, which enabled large stores to operate 24
hours per day in principle. To account for the effect of this deregulation, we calculate
the percentage of people who shop during the period from 8:00 pm to 8:00 am using

12

STULA, as a proxy for the needs of consumers shopping at night. In STULA, there isan activity called shopping among 20 possible activities. We use 1 to indicate anindividual who did shopping for at least 15 minutes from 8:00 pm to 8:00 am and 0
otherwise, and calculate the percentage of people who shop during the period byprefecture. In order to capture the effect of the changes in the legislation only, we use
only nonworker samples to calculate the shopping rate.
Lastly, we include regional male unemployment rates in order to control for thetightness of the local labor market.

Adjusted Timing of Work
Tables 5(1) to 5(4) show the results of the Oaxaca–Blinder decomposition of
nonregular employee’s employment rates for four undesirable times: (1) midnight, (2)3:00 am, (3) 10:00 pm and (4) 11:00 pm. First, looking at midnight in Table 5(1) whenthe employment rate increased by 4 % from 1996 to 2006, age is the only component
that significantly explains the increase in the employment rate. Because the average age
decreased from 45.6 to 42.3, the growing number of younger employees is one of thefactors explaining the rise in the employment rate of nonregular employees at midnight.
Otherwise, however, the table confirms that there is virtually no change even after
controlling for changes in demography and the occupational mix.
Table 5(2) for 3:00 am also shows that even after controlling for various factors,
two-thirds of the increase in the employment rate at this time is still unexplained. The
increase in the number of single workers is the only explained factor at this time, while
the blue-collar dummy shows a significantly negative contribution in the unexplained
factor.
Next, the results shown in Table 5(3) for 10:00 pm provide a somewhat different
picture in that most of the increase in the employment rate is explained by the changes
in the control variables. Increases in the percentage of young and single employees areagain significant at the 5 % level. Furthermore, the increase in the average hours
worked by regular employees explains almost three-quarters of the total change in the13employment rate. We interpret this finding to imply that there have been increases in the
demand for services and goods at later hours on the way home by regular employees
who work until night. It is inferred that the late night wage premium to meet thisdemand consequently induced nonregular employees’ labor supply at this time.
However, when we look at the result for 11:00 pm, age is the only variable thatis significant as the explained factor. Instead, the share of the service industry,
percentage of people shopping from 8:00 pm to 8:00 am, and regional unemployment
rate are significant as the unexplained factor.

Interpreting the increase in night work of nonregular employees
To summarize, the Oaxaca–Blinder type decomposition of the changes innonregular employee’s employment rates during undesirable times in Tables 5(1) to5(4) show that most of the increases are not explained by changes in demographic,
occupational, or industrial composition, as well as other factors such as deregulation ofoperating hours for large retailers. The exception is the regular employee’s working
hours that have a positive effect on the nonregular employee’s employment rate at 10
pm. How should we interpret these results?
One possibility is that the large unexplained factor leading to the increase innighttime employment rates is the negative income effects of nonregular employees,
which is the opposite of the phenomenon observed in the US. As we explained,
Hamermesh (1999a) found a decline in US employment rates at night along with anincrease in the average real wages. Conversely, the Japanese labor market experienced
declining real wages after the bursting of the bubble economy, which would haveinduced negative income effects on the timing of work especially for the low wage
earners such as nonregular employees. That is, the more the workers’ potential market
wages decline, the more they tend to take jobs at undesirable hours to compensate forthe (potential) income loss.
Another interpretation is related to the sustained recession in post-bubble Japanthat reduced the number of regular employees working daytime hours, while there was a14

trend among businesses, particularly in the service industry, to greatly expand operating
hours in the hope of sparking at least some demand. This may have resulted in the more
highly educated, higher income employees working during the desirable daytime hours
as regular employees, while the other workers, having been squeezed out, had no choice
but to work at other times.9 We assume these factors, coming both from the labor
supply and demand sides, brought about the increase in the employment rate ofnonregular employees at undesirable times.
Then, how should we evaluate these increases in employment rates ofnonregular employees at undesirable hours? As far as consumers who work overtime
are able to purchase services and goods on their way home, or the workers who fail tofind a job during daytime are able to get nonregular jobs at night, it may be a better
outcome for all workers. However, issues such as health problems caused by nighttime
work also cannot be ignored. It is sometimes argued that night work as well as long
working hours could adversely affect one’s health.
In fact, we can observe that the increase in the nighttime employment rate isaccompanied by longer working hours. Fig. 2 is a radar chart where we plot the average
daily work hours for those who work at each time of the day. It is found that the solidline (the average hours worked in 2006) expands to the northeast direction from thedotted line (those in 1996), which indicates the increasing average hours worked for
those who work from midnight to 6:00 am. This indicates that the average hours worked
for those working from midnight to early morning increased in 2006. Furthermore, Fig.
2 suggests that the average hours worked by nonregular employees who work frommidnight to early morning in 2006 is almost the same length as that of daytime regular
employees in 1996 (shown using triangle dots). It is important to note that we haveshown in Table 2 that the average hours worked by all nonregular employees is much
shorter than that of regular employees, and has not changed during the decade. However,Fig. 2 indicates that nonregular employees who work during undesirable night hours
9

An increase in the fraction of workers working at unusual times as a result of wider use of theinternet could be another possibility. This is an area for further study.

15

began to work as many hours in 2006 as that of daytime regular employees. Thisfinding may also be evidence of the negative income effect for those who work during
undesirable times as described in Section II. That is, workers who need to earn more at
low wage rates tend to work longer hours to earn more income.
VI. Conclusion
This paper aimed to understand Japanese worker’s recent lifestyle changes byobserving the timing of work during the day, using a Japanese time use survey from1996 to 2006.
We showed that Japan had a noteworthy increase in the share of employees
working at unusual times (late night and early morning) over a decade starting in themid 1990s. When controlling for changes in hours worked, however, we found that thenotable increase in the fraction of people at work at such unusual times was evident for
low-income nonregular employees while relatively higher-income regular employees’
work timing remained stable. These observations imply that there is a trend ofdiversification of work timing in Japan between regular and nonregular employees,
suggesting another aspect of inequality.10 The increase in the employment rate duringlate night and early-morning hours, which are generally thought of as undesirable hours
with a high marginal disutility of work, is an interesting result, because Hamermesh(1999a) found opposite results: a decline in the late night and early-morning
employment rate in the US.
Why has the employment rate for nonregular employees during late night andearly-morning hours increased in Japan? We pointed out a possible explanation in thatthe increase in the average hours worked per weekday by regular employees possibly
because of the spread of the five-day work week increased the demand for services andgoods at later hours as workers returned home. An Oaxaca–Blinder type decomposition10

Kuroda and Yamamoto (2010) showed that notable increases in the late night and very

early-morning employment rates since the mid 1980s was evident among full-time workers with lowlevels of both education and income in Japan.

16

suggested that such increases in the average hours worked by regular employees
explains partially the rise in the employment rate of nonregular employees at unusual
times. However, unexplained factors remain. We conclude that the remaining factor
relates to the negative income effect, which induces low-wage nonregular employees totake jobs at night to earn a wage premium. Another interpretation is that the job
opportunities are limited to nonregular work at night, thus people have no choice but toaccept jobs at those undesirable times because of the prolonged recession.
This growth in work timing differences during a sustained economic slump
could probably be interpreted as evidence that people were happy just to have theopportunity to work, even at undesirable times. If that is the case, income inequality islower than it would have been with absolutely no change in the work timing gap. In
other words, another way to frame these phenomena is that although gaps in the timingof work arose during Japan’s lost decade, this was a successful way to avoid
unemployment and brought the added benefit of suppressing the increase in income
inequality.
There has been an increase in health problems related to overworking and stressin Japan in the last several years; however, this may be related to the rising number ofpeople working late night and early-morning hours. Some interesting issues for further
study are the causes of differences in the timing of work and whether late-night work
has anything to do with Japan’s increase in overworking and stress-related healthproblems.

17

References
Fairlie, R. W. (2005) An extension of the Blinder-Oaxaca decomposition technique tologit and probit models, Journal of Economic and Social Measurement, 30,
305–316.
Gersbuny, J. and Sullivan, O. (1998) The sociological uses of time use diary analysis,
European Sociological Review, 14, 69-85.
Hamermesh, D. S. (1999a) The timing of work over time, The Economic Journal, 109,
37-66.
(1999b) Crime and the timing of work, Journal of Urban Economics, 45,
311-330.
(2002) Timing, togetherness and time windfalls, Journal of Population
Economics, 15, 601–623.
Jann, B. (2008) The Blinder-Oaxaca decomposition for linear regression models, The
Stata Journal, 8, 453-479.
Kawaguchi, D., Naitou, H. and Yokoyama, I. (2008) Labor market responses to legal
work hour restriction: evidence from Japan, ESRI Discussion Paper Series
No.202, Economic and Social Research Institute, Cabinet Office, Governmentof Japan.
Kuroda, S., (2010) Do Japanese work shorter hours than before? measuring trends inmarket work and leisure using 1976-2006 Japanese time-use survey, Journal ofJapaneseandInternational

Economies,

forthcoming(doi:10.1016/j.jjie.2010.05.001).
and Yamamoto, I. (2010) When do people work? evidence of growing
inequality in work timing using a Japanese time use survey, unpublished paper.
Ohta, K., (2005) Rise in earnings inequality in Japan-- a sign of bipolarization?, paper
presented at ESRI international conference Options for Sustainable Economic
Growth in Japan, Economic and Social Research Institute, Cabinet Office,
Government of Japan.
Presser, H. B. (1987) Work shifts of full-time dual-earner couples: patterns and contrasts
18

by sex of spouse, Demography, 24, 99-112.
Rosen, S. (1986) The theory of equalizing differences, in Handbook of Labor
Economics, (Eds) O. Ashenfelter and R. Layard, North-Holland, Amsterdam,
641-692.
Szalai, A. (1972) The use of time, Mouton, The Hague.
Winston, G. C. (1982) The timing of economic activities, Cambridge University Press,
New York.

19

Table 1: Basic statistics

Regular employees
Age

41.12

(10.98)43.28(15.18)

Education (university graduates = 1)0.34

(0.47)

0.19(0.39)

Marital status (married = 1)0.72

(0.45)

0.49(0.50)

Child (having child = 1)0.18

(0.38)

0.04(0.19)

Occupations

Professional + technical0.16(0.36)

0.10(0.29)

Managerial

0.04(0.19)

0.00(0.06)

Clerical

0.18(0.38)

0.10(0.30)

Sales

0.15

(0.36)

0.08(0.28)

Blue collar

0.48(0.50)

0.72(0.45)

8.98(3.28)

6.75(3.75)

Average hours worked per day

88801

Sample sizes

Notes:

Nonregular employees

Weekday (Monday through Friday) respondents.
Standard deviations are given in parentheses.

20

8052

Table 2: Employment Rate by Time

Regular employees
1996
2001
2006
96 --> 06
Nonregular employees
1996
2001
2006
96 --> 06

midnight

3:00 am

5:00 am

11:00 am

7:00 pm

10:00 pm

11:00 pm

0.036
0.042
0.042
0.006 **

0.024
0.025
0.029
0.004 **

0.032
0.032
0.035
0.003

0.853
0.841
0.853
0.000

0.305
0.340
0.359
0.054 **

0.077
0.092
0.094
0.017 **

0.054
0.063
0.062
0.008 **

0.041
0.062
0.084
0.043 **

0.025
0.045
0.057
0.032 **

0.038
0.691
0.056
0.620
0.066
0.635
0.028 ** -0.056 **

0.151
0.167
0.210
0.059 **

0.070
0.084
0.097
0.027 **

0.053
0.074
0.083
0.030 ***

Note: +, *, ** indicate 10, 5, 1 % statistical significance, respectively.

21

Table 3: Average Hours Worked Per Day

Weekday
Saturday
SundayRegular employees
1996
2001
2006
8.86
8.87
9.21
4.97
4.58
4.47
2.16
2.16
2.23

change96->060.34 **-0.49 **
0.07 *

Nonregular employees
1996
2001
2006
6.76
6.58
6.86
4.98
4.64
4.70
2.52
2.36
2.58

Note: +, *, ** indicate 10, 5, 1 % statistical significance, respectively.

22change96->060.10-0.28 *
0.07

Table 4: Employment Rate Decomposition (Adjusting the Number of Hours
Worked)midnight

3:00 am

5:00 amRegular employees
difference(explained)(unexplained)

0.006
0.002 **
0.004 +

0.004
0.002 **
0.002

Nonregular employees
difference(explained)(unexplained)

0.043
0.003
0.040 **

0.032
0.003
0.030 **

11:00 am

7:00 pm

10:00 pm

11:00 pm

0.003
0.000
0.003 ** 0.012 **0.002-0.012 **0.054
0.046 **
0.009 +

0.017
0.015 **
0.003

0.008
0.007 **
0.001

0.028
-0.0560.003
0.002
0.026 ** -0.059 **

0.059
0.011
0.049 **

0.027
0.003
0.024 *

0.030
0.003
0.027 **

Notes: ‘difference’ = employment rate at time t in 2006 – employment rate at time t in 1996.
+, *, ** indicate 10, 5, 1 % statistical significance, respectively.

23

Table 5: Employment Rate Decomposition (Adjusting for Demography and Other
Possible Changes)(1) Midnight

Mean
Year 2006

Dependent variable
Employment rate at midnight

Estimated coefficients

Oaxaca decomposition

Year 1996

Year 2006

Explained

UnexplainedYear 1996

0.084

0.041

-

-

0.00890.0336+(0.277)(0.198)--(0.015)(0.018)

6.861

6.762

0.1131**

0.0935**0.00160.0178(3.829)(3.647)(0.021)(0.019)(0.003)(0.030)42.29745.645-0.0112*-0.0132*

0.0059+0.0117(14.825)(15.180)(0.005)(0.006)(0.003)(0.044)Control variables
The number of hours worked

Age
Education (university graduates = 1)

Marital status (married = 1)

Child (having child = 1)

Share of service industry in prefecture

0.203

0.174

0.0682-0.15830.00020.0054(0.402)(0.379)(0.174)(0.212)(0.001)(0.007)

0.420

0.592

-0.2298-0.14310.0055-0.0063(0.494)(0.492)(0.153)(0.145)(0.004)(0.016)

0.035

0.045

-0.1396-0.06460.0002-0.0004(0.184)(0.207)(0.220)(0.257)(0.000)(0.002)

0.623

0.578

1.19650.17080.00730.0804(0.098)(0.091)(0.773)(0.808)(0.007)(0.094)

Occupations: (base = Clerical)
Professional and technical

Sales

Blue collar

0.085

0.116

-0.8394*-0.1160

0.0029-0.0102(0.279)(0.320)(0.404)(0.347)(0.002)(0.008)

0.081

0.080

0.09210.07740.00000.0002(0.272)(0.271)(0.402)(0.355)(0.000)(0.006)-0.0100

0.729

0.682

0.09010.19650.0008(0.444)(0.466)(0.373)(0.299)(0.002)(0.044)0.1699-0.0067-0.4273(0.420)

Averege hours worked
by regular employees

9.203

8.854

-0.1886(0.274)(0.184)(0.187)(0.285)(0.012)

Percentage of people shoppingfrom 8 pm to 8 am

1.174

0.754

-0.0707-0.3300*-0.0106

0.0310(0.386)(0.380)(0.168)(0.161)(0.012)(0.027)

Regional unemployment rate

Constant

4.859

3.845

0.0329-0.09640.00200.0692(1.026)(0.559)(0.073)(0.110)(0.010)(0.072)---0.8985-2.9353

0.2722--(1.837)(2.741)(0.440)Notes: Numbers in parentheses are robust standard errors.
+, *, ** indicate 10, 5, 1 % statistical significance, respectively.
The number of observations is 2,945 for year 2006 and 2,767 for year 1996.

24

Table 5: Employment Rate Decomposition (Adjusting for Demography and Other
Possible Changes)(2) 3:00 am

Mean
Year 2006

Dependent variable
Employment rate at midnight

Estimated coefficients

Oaxaca decomposition

Year 1996

Year 2006

Explained

UnexplainedYear 1996

0.057

0.025

-

-

0.0101

0.0218+(0.231)(0.155)--(0.008)(0.013)

6.861

6.762

0.1296**0.0806**0.00110.0234(3.829)(3.647)(0.031)(0.018)(0.002)(0.025)42.29745.645-0.0011-0.0092+0.00130.0252(14.825)(15.180)(0.005)(0.005)(0.001)(0.022)

0.203

0.174

-0.0005

0.22190.0002-0.0029(0.402)(0.379)(0.213)(0.228)(0.001)(0.004)

0.420

0.592

-0.3075*-0.4235*

0.0055*0.0046(0.494)(0.492)(0.142)(0.177)(0.002)(0.008)Control variables
The number of hours worked

Age
Education (university graduates = 1)

Marital status (married = 1)

Child (having child = 1)

Share of service industry in prefecture

0.035

0.045

0.3496

0.2631-0.0004

0.0003(0.184)(0.207)(0.234)(0.284)(0.000)(0.001)

0.623

0.578

-0.2561-2.9355**-0.00360.1104(0.098)(0.091)(0.795)(0.754)(0.003)(0.069)

Occupations: (base = Clerical)
Professional and technical

Sales

Blue collar

0.085

0.116

-1.4876**

0.16910.0033-0.0126(0.279)(0.320)(0.517)(0.405)(0.002)(0.008)

0.081

0.080

-0.38620.3849-0.0000-0.0044(0.272)(0.271)(0.445)(0.296)(0.000)(0.004)

0.729

0.682

-0.14310.9118**0.0001-0.0516+(0.444)(0.466)(0.406)(0.248)(0.001)(0.029)-0.00540.00030.0078(0.236)

Averege hours worked
by regular employees

9.203

8.854

0.0072(0.274)(0.184)(0.188)(0.329)(0.006)Percentage of people shoppingfrom 8 pm to 8 am

1.174

0.754

-0.0560-0.0863-0.00190.0013(0.386)(0.380)(0.190)(0.174)(0.007)(0.016)

Regional unemployment rate

Constant

4.859

3.845

0.01630.2030*0.0042-0.0520(1.026)(0.559)(0.069)(0.102)(0.006)(0.045)---2.2286-1.8350-0.0276--(1.755)(3.069)(0.247)

Note: See Table 5(1).

25

Table 5: Employment Rate Decomposition (Adjusting for Demography and Other
Possible Changes)(3) 10:00 pm

Mean
Year 2006

Dependent variable
Employment rate at midnight

Estimated coefficients

Oaxaca decomposition

Year 1996

Year 2006

Year 1996

Explained

Unexplained

0.097

0.070

-

-

0.0235+0.0027(0.297)(0.256)--(0.013)(0.015)

6.861

6.762

0.1092**0.1219**0.0017-0.0098(3.829)(3.647)(0.018)(0.017)(0.003)(0.012)42.29745.645-0.0101*-0.0104*0.0049*0.0013(14.825)(15.180)(0.005)(0.004)(0.002)(0.032)

0.203

0.174

-0.0127-0.3979*-0.0005

0.0079(0.402)(0.379)(0.152)(0.159)(0.001)(0.018)

0.420

0.592

-0.3148**-0.05130.0061*-0.0160(0.494)(0.492)(0.121)(0.116)(0.003)(0.040)Control variables
The number of hours worked

Age
Education (university graduates = 1)

Marital status (married = 1)

Child (having child = 1)

Share of service industry in prefecture

0.035

0.045

0.2802-0.0609-0.00020.0016(0.184)(0.207)(0.185)(0.229)(0.000)(0.004)

0.623

0.578

-1.1384+

0.8170-0.0034-0.1322(0.098)(0.091)

Occupations: (base = Clerical)
Professional and technical

Sales

Blue collar(0.659)(0.680)(0.004)(0.297)(0.237)(0.166)(0.001)(0.010)

0.085

0.116

0.34200.2932-0.00150.0005(0.279)(0.320)(0.231)(0.244)(0.001)(0.004)

0.081

0.080

0.2265-0.10370.00000.0030(0.272)(0.271)(0.217)(0.255)(0.000)(0.008)

0.729

0.682

0.0725-0.0908

0.00000.0132(0.444)(0.466)(0.176)(0.187)(0.001)(0.037)

Averege hours worked
by regular employees

9.203

8.854

0.26880.10310.0144*0.1675(0.274)(0.184)(0.175)(0.244)(0.007)(0.501)

Percentage of people shoppingfrom 8 pm to 8 am

1.174

0.754

0.0398-0.2724*-0.0069

0.0336(0.386)(0.380)(0.128)(0.129)(0.007)(0.076)

Regional unemployment rate

Constant

4.859

3.845

0.1224*-0.2127*0.00900.1544(1.026)(0.559)(0.060)(0.096)(0.007)(0.348)---4.1655*-2.2136-0.2223--(1.691)(2.333)(0.624)

Note: See Table 5(1).

26

Table 5: Employment Rate Decomposition (Adjusting for Demography and Other
Possible Changes)(4) 11:00 pm

Mean
Year 2006

Dependent variable
Employment rate at midnight

Estimated coefficients

Oaxaca decomposition

Year 1996

Year 2006

ExplainedYear 1996

Unexplained

0.083

0.053

-

-

0.01650.0130(0.276)(0.224)--(0.013)(0.014)

6.861

6.762

0.0941**0.1187**0.0014-0.0147(3.829)(3.647)(0.018)(0.021)(0.002)(0.012)42.29745.645-0.0082+-0.0151**

0.0044*0.0272(14.825)(15.180)(0.005)(0.005)(0.002)(0.028)Control variables
The number of hours worked

Age
Education (university graduates = 1)

Marital status (married = 1)

Child (having child = 1)

Share of service industry in prefecture

0.203

0.174

0.1081-0.5359**-0.00020.0102(0.402)(0.379)(0.154)(0.203)(0.001)(0.006)

0.420

0.592

-0.2660*

0.11440.0039-0.0181(0.494)(0.492)(0.121)(0.126)(0.002)(0.013)

0.035

0.045

0.2389-0.1680-0.0001

0.0015(0.184)(0.207)(0.185)(0.220)(0.000)(0.001)

0.623

0.578

-1.0186

1.4134+-0.0016-0.1270+(0.098)(0.091)(0.671)(0.778)(0.003)(0.067)

Occupations: (base = Clerical)
Professional and technical

Sales

Blue collar

0.085

0.116

0.6336*0.1167-0.00190.0047(0.279)(0.320)(0.290)(0.318)(0.001)(0.005)

0.081

0.080

0.6917*-0.17470.00000.0062(0.272)(0.271)(0.270)(0.308)(0.001)(0.004)

0.729

0.682

0.6852**-0.0225

0.00230.0440(0.444)(0.466)(0.225)(0.228)(0.001)(0.033)

Averege hours worked
by regular employees

9.203

8.854

0.0742-0.2363

0.0026

0.2429(0.274)(0.184)(0.178)(0.250)(0.008)(0.255)Percentage of people shoppingfrom 8 pm to 8 am

1.174

0.754

0.0945-0.3320*-0.00440.0345+(0.386)(0.380)(0.133)(0.144)(0.007)(0.020)Regional unemployment rate

Constant

4.859

3.845

0.1452*-0.2566*

0.01020.1429*(1.026)(0.559)(0.062)(0.109)(0.007)(0.069)---3.2396+0.6348-0.3414--(1.771)(2.414)(0.301)

Note: See Table 5(1).

27Fig. 1: Employment rate by time on weekdays (all male employees)(1) Regular Employees
1.0
0.9

1996

0.8

2006

0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
midnight

3:00 am

6:00 am

9:00 amnoon

3:00 pm

6:00 pm

9:00 pm

9:00 amnoon

3:00 pm

6:00 pm

9:00 pm(2) Nonregular Employees
1.0
0.9
0.8

1996
2006

0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
midnight

3:00 am

6:00 am

Note: Regular and nonregular employees (including students) aged 23 to 64. Self-employed are
excluded.

28

Fig. 2: Average daily work hours by time of the day

Nonregular 1996
Nonregular 2006

midnight
12.0

Regular 1996

9:00 pm

3:00 am
10.0

8.0

6:00 pm

6:00 am

6.0

3:00 pm

9:00 amnoon

29