Melbourne Institute Working Paper Series
Working Paper No. 7/16
Use It Too Much and Lose It?
The Effect of Working Hours on Cognitive Ability
Shinya Kajitani, Colin McKenzie and Kei Sakata

Use It Too Much and Lose It?
The Effect of Working Hours on Cognitive Ability*
Shinya Kajitani†, Colin McKenzie‡ and Kei Sakata§†

Faculty of Economics, Meisei University; and Melbourne Institute ofApplied Economic and Social Research, The University of Melbourne‡
Faculty of Economics, Keio University§
Faculty of Economics, Ritsumeikan University

Melbourne Institute Working Paper No. 7/16
ISSN 1328-4991 (Print)
ISSN 1447-5863 (Online)
ISBN 978-0-7340-4405-1
February 2016
* We would like to thank Jongsay Yong for his helpful comments and suggestions. The first
and third authors gratefully acknowledge the financial assistance of a Japan Society for the
Promotion of Science (JSPS) Grant in Aid for Scientific Research (B) No. 24330093 for a
project on “Retirement Behaviour of the Aged and their Cognitive Ability and Health”. The
first author also gratefully acknowledges the financial assistance of a grant from the Meisei
University Special Research Leave Program Fund for a project on “The Impact of theWorking Hours on Health and Cognitive Functioning for Middle-aged and Older
Australians”. The second author gratefully acknowledges the financial assistance of a grantfrom the Fund to Promote Academic Research for a project on “Empirical Research on
Responses to the Aging Problems of Japan’s Economy”. This paper uses unit record datafrom the Household, Income and Labour Dynamics in Australia (HILDA) Survey. The
HILDA Project was initiated and is funded by the Australian Government Department ofSocial Services (DSS) and is managed by the Melbourne Institute of Applied Economic andSocial Research (Melbourne Institute). The findings and views reported in this paper,
however, are those of the authors and should not be attributed to either DSS or the Melbourne
Institute. No ethic approval was required for this study. Corresponding author: Colin
McKenzie <mckenzie@z8.keio.jp>.

Melbourne Institute of Applied Economic and Social Research
The University of Melbourne
Victoria 3010 Australia
Telephone (03) 8344 2100
Fax (03) 8344 2111
Email melb-inst@unimelb.edu.au
WWW Address http://www.melbourneinstitute.com

Abstract
Using data from Wave 12 of the Household, Income and Labour Dynamics in Australia(HILDA) Survey, we examine the impact of working hours on the cognitive ability of people
living in Australia aged 40 years and older. Three measures of cognitive ability are
employed: the Backward Digit Span; the Symbol Digits Modalities; and a 25-item version of
the National Adult Reading Test. In order to capture the potential non-linear dependence ofcognitive ability on working hours, the model for cognitive ability includes working hours
and its square. We deal with the potential endogeneity of the decision of how many hours towork by using the instrumental variable estimation technique. Our findings show that there isa non-linearity in the effect of working hours on cognitive functioning. For working hours up
to around 25 hours a week, an increase in working hours has a positive impact on cognitive
functioning. However, when working hours exceed 25 hours per week, an increase inworking hours has a negative impact on cognition. Interestingly, there is no statisticaldifference in the effects of working hours on cognitive functioning between men and women.
JEL classification: I10, J22, J26
Keywords: Cognitive ability, endogeneity, retirement, working hours

21. Introduction
Many countries have already increased their retirement ages by delaying the age at
which people are eligible to start receiving pension payments. This means that more
people continue to work in the later stages of their life. Some claim that delaying theretirement age can potentially help reduce the deterioration of cognitive functioning
because of the continued intellectual stimulation that working provides (Potter et al.,2008; Small, 2002). The relationship between retirement and cognitive functioning has
attracted much attention in recent years, but recent studies have not reached consensus onwhether the so called ‘use it or lose it’ hypothesis is valid. After controlling for theendogeneity of retirement, Mazzonna and Peracchi (2012) and Rohwedder and Willis(2010) find that there was a significant and negative effect of retirement on cognitive
skills, while Coe and Zamarro (2011) do not find such a causal effect. Bonsang et al.
(2012) find that the effects of retirement on cognitive function appeared with a lag, andconclude that there were positive externalities of a delayed retirement for older
individuals.
Although these previous studies provide important insights into the relationshipbetween retirement and cognitive functioning, they do not examine the impact of thequality or quantity of work on cognitive functioning. Work can be a double edged sword,in that it can stimulate brain activity, but at the same time, long working hours andcertain types of tasks can cause fatigue and stress which potentially damage cognitive
functions. Thus, the degree of intellectual stimulation of work may depend on therequired task and working hours, that is, the quality and the quantity of work. There arenumber of studies which examine the effects of the quality of work (job type and jobtask) on cognitive functioning (Schooler et al., 1999; Bosma et al., 2003; Potter et al.,2008; Finkel et al., 2009; Marquié et al., 2010; Smart et al., 2014).
However, there seem to be extremely few studies discussing the impact of thequantity of work (working hours) on cognitive functioning. Working individuals withlonger hours of work have more incentive to invest in cognitive repair activities in orderto maintain their cognition while working longer. In contrast, longer hours of work per se
could reduce their cognitive performance. Using the Whitehall II Study sample of British
civil servants, Virtanen et al. (2009) examine the relationship between long working
hours and cognitive skills in middle age. They find that vocabulary test scores whichmeasure crystallized intelligence are relatively lower among workers with long working
hours, and point out that long working hours may have a negative effect on cognition in3

middle age. However, Virtanen et al. (2009) do not compare the level of cognitive skillsof workers and non-workers. Middle aged and elderly persons tend to retire or decrease
their working hours by being employed as a non-regular worker, so it is important toexamine the impact of working hours on cognitive functioning among middle-aged andolder adults.
What are the channels in which labor hours affect cognitive functioning? One of thechannels is physical and/or psychological stress. Medical research suggests that stressaffects cognitive functioning. McEwen and Sapolsky (1995) indicate that stress affects
cognition rapidly via catecholamines and more slowly via glucocorticoids. Martin et al.
(2011) find that chronic stress has effects on cognition and increases the vulnerability tomental illness. Proctor et al. (1996) indicate that long working hours have adverse effects
on the mental health of workers in the automobile industry. Cottini and Lucifora (2013)
also find that long working hours increase stress. Thus, although engaging in work may
help reduce the pace of cognitive impairment, such positive effects may be offset by thenegative impacts caused by mental and physical stress associated with long labor hours.
In this paper, we focus not on labor market participation (the extensive margin), but
on working hours (the intensive margin). We examine the causal impact of working
hours on cognitive functioning for middle-aged and older adults using a cross section
sample from the Household, Income and Labour Dynamics in Australia (HILDA) Survey.
We deal with the potential endogeneity of decisions on working hours by using the
instrumental variable estimation technique. One potential problem in using working
hours as the variable of interest is that the working hours are left censored, that is, forindividuals who are retired or unemployed, working hours are treated as zero. In order totake account of these zero values in the working hours, we apply a Tobit model and thenuse the nonlinear fitted values from the Tobit model as the new instrument for working
hours when the model for cognitive functioning is estimated by two stage least squares(2SLS).
Our empirical evidence shows that there is non-linearity in the effects of working
hours on cognitive functioning. When working hours are less than around 25 hours aweek, working hours have a positive impact on cognitive functioning. However, whenworking hours are more than 25 hours per week, working hours have negative impacts
on cognition. These results suggest that people in old age could maintain their cognitive
ability by working in a part-time job that requires them to work around 20–30 hours per
week.

4

We estimate our models on samples of males and females separately as Matud(2004) suggests that there are differences in the extent to which males and females suffer
stress and cope with stress. Since stress is suggested as one of the reasons for labor hours
affecting cognitive functioning, Matud’s evidence suggests a possible difference in theconnection between working hours and cognitive functioning for men and women.
However, we find that there is no statistically significant gender difference in the effects
of working hours on cognitive functioning.
The rest of this paper is organized as follows: Section 2 presents the empiricalframework used in this paper. Section 3 describes the data and Section 4 reports theresults of estimation and discusses their implications. The last section concludes thispaper.

2. Estimation model and identification strategy
Our identification strategy exploits the variation in working hours, while controllingfor individual characteristics. In order to capture a possible non-linearity in the effects ofworking hours on cognitive functioning, we consider the following model:

𝐶𝐶𝐶𝑖 = 𝛼1 𝑊𝑊𝑖 2 + 𝛼2 𝑊𝑊𝑖 + 𝑋𝑖 𝛽 + 𝑢𝑖 ,(1)

where 𝐶𝐶𝐶𝑖 denotes a cognitive test score, 𝑊𝑊𝑖 2 is the square of working hours, and𝑊𝑊𝑖 is working hours. 𝑋𝑖 denotes a vector of control variables which consists of aconstant, the respondent’s age, age squared, dummy variables which indicate his/heryears of education, and a dummy variable which indicates the type of his/her educational
qualification. We also include a dummy variable which takes the value unity if the
respondent has a spouse and zero otherwise. This variable is included because
communications and interactions with other family members may prevent declines incognitive functioning. 𝑢𝑖 is an error term, and the subscript 𝑖 refers to the 𝑖th individual.

The coefficient 𝛼1 captures the non-linear effect of working hours on cognitive

functioning. Given the discussion in section 1 that some work is better than no work, andthat too much work may be worse than some work, it is expected that 𝛼1 < 0 and
𝛼2 > 0. Holding everything else constant, it is easy to see that the cognitive test score is

maximized when 𝑊𝑊𝑖 = −𝛼2 /(2𝛼1 ).

5The possibility of the endogeneity of the respondents’ working hours in equation (1)is a major obstacle to estimating the causal impact of working hours on cognitive
functioning. Individuals whose cognitive abilities are lower (or higher) may decide toleave the workforce earlier (or later). On the other hand, the reverse causality between
cognitive skills and working hours can be more ambiguous. Previous studies observe thata high wage rate is associated with cognitive skills (for example, Capatina, 2014). In aneoclassical model of consumer behavior where there is a trade-off between
consumption and leisure (leisure is a normal good), the impact of the wage rate on
working hours depends on whether the substitution effect dominates the income effect orvice versa. Individuals whose cognitive abilities are higher, who tend to earn a relatively
higher wage, could decide to reduce their hours of work even further.
The standard two stage least squares (2SLS) procedure is to find instruments whichindicate the factors of labor demand or the factors which are related to their labor supply,
but unrelated to their cognitive skills. However, we have another issue in examining theeffects of labor hours on cognitive functioning, that is, labor hours are censored (that is,retirees report zero working hours). Rather than directly using variables which correlatewith labor hours, but do not correlate with cognitive functioning, we use these variables
for creating the fitted values for squared of working hours and working hours as
instruments. The following model is assumed to explain working hours:

𝑊𝑊𝑖∗ = 𝛾1 𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑟𝑟𝑟𝑟𝑖 + 𝛾2 𝐼𝐼𝐼𝐼𝐼 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑖 + 𝛾3 𝑂𝑂𝑂𝑂𝑂 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑖 + 𝛾4 𝑅𝑅𝑅𝑅𝑅𝑅𝑖+ 𝛾5 𝑉𝑉𝑉𝑉 𝑟𝑟𝑟𝑟𝑟𝑒𝑖 + 𝛾6 𝑁𝑁𝑁𝑁𝑁𝑁 𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑐ℎ𝑖𝑖𝑖𝑖𝑖𝑖𝑖+ 𝛾7 𝑃𝑃𝑃𝑃𝑃𝑃 𝑖𝑖 𝑠𝑠𝑠𝑠𝑠 𝑎𝑎𝑎𝑎𝑎𝑖 + 𝛾8 𝑂𝑂ℎ𝑒𝑒 𝑝𝑝𝑝𝑝𝑝𝑝 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑖+ 𝛾9 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑖 + 𝛾10 𝑊𝑊𝑊𝑊 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑖 + 𝛾11 𝑂𝑂𝑂 ℎ𝑜𝑜𝑜𝑜𝑖+ 𝑋𝑖 𝛿 + 𝑒𝑖

(2),

if 𝑊𝑊𝑖∗ ≤ 0

𝑊𝑊𝑖 = 0= 𝑊𝑊𝑖∗

if 0 < 𝑊𝑊𝑖∗ ,where 𝑊𝑊𝑖∗ denotes an unobserved latent variable which is connected to the observed
working hours 𝑊𝑊𝑖 . 𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑟𝑟𝑟𝑟𝑖 is the job vacancy over the number of employedpersons in the state where individual i lives. 𝐼𝐼𝐼𝐼𝐼 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑖 , 𝑂𝑂𝑂𝑂𝑂 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑖 ,𝑅𝑅𝑅𝑅𝑅𝑅𝑖 , and 𝑉𝑉𝑉𝑉 𝑟𝑟𝑚𝑚𝑚𝑚𝑖 are 0–1 dummy variables taking the value unity if the6respondent lives in the relevant area, respectively. These variables are designed tocapture factors related to labor demand. On the other hand, 𝑁𝑁𝑁𝑁𝑁𝑁 𝑜𝑓 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑

𝑐ℎ𝑖𝑖𝑖𝑟𝑒𝑒𝑖 denotes the number of dependent children under the age of 24 years old in
his/her household, 𝑃𝑃𝑃𝑃𝑃𝑃 𝑎𝑎𝑎𝑎𝑎𝑖 indicates whether his/her father or mother still alive,
and 𝑂𝑂ℎ𝑒𝑒 𝑝𝑝𝑝𝑝𝑝𝑝 𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑏𝑖 indicates whether he/she receives public payments except

the Age Pension. 𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴𝐴 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑖 indicates whether the respondent is an Australian
citizen, 𝑊𝑊𝑊𝑊 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑖 is the number of years of work experience the respondenthas, and 𝑂𝑂𝑂 ℎ𝑜𝑜𝑜𝑜𝑖 is a dummy that indicates whether the respondent owns his/herhouse. These variables are designed to capture the factors which impact on the labor

supply of the respondent, but not on their cognitive functioning. 1 𝑋𝑖 is the same vector ofcontrol variables as is used in equation (1), and 𝑒𝑖 is a disturbance which is assumed to

be normally independently and identically distributed with a zero mean and variance 𝜎 2 .

For a retiree or an unemployed person, we observe his/her working hours per week aszero. Therefore, we estimate this model with left censoring using the Tobit technique.

First, we estimate the parameters in equation (2) using a Tobit estimator to obtain
estimates of the parameters of 𝛾𝑘 (𝑘 = 1, ⋯ , 11) and 𝛿 , 𝛾
�𝑘 and 𝛿̂ , respectively. Fromequation (2), the conditional expectations of 𝑊𝑊𝑖 can be computed as
𝐸(𝑊𝑊𝑖 |𝑍𝑖 ) = Φ �

𝑍𝑖 𝜀
𝑍𝑖 𝜀
� 𝑍𝑖 𝜀 + 𝜎𝜎 � �
𝜎
𝜎

(3).

Where 𝑍𝑖 is the vector of regressors in equation (2), 𝜀 is the vector of parameters inequation (2), Φ(∙) is the cumulative distribution function of the standard normal

distribution function, and 𝜙(∙) is the probability distribution function (see Greene 2008,

p. 871). Given estimates of the parameters of equation (2), this conditional expectation2�𝚤 . 𝑊𝑊�𝚤 and 𝑊𝑊�𝚤 are used as instruments for 𝑊𝑊𝑖 and 𝑊𝑊𝑖 2 ,can be estimated as 𝑊𝑊
respectively, in equation (1) in a 2SLS procedure (see Wooldridge 2010, p. 268).

1 It

might be argued that the cognitive test score may be correlated with the location of theindividual’s residence or with the dummy variable which indicates whether the individual’s parents
are still alive. The validity of the variables used to generate exclusion restrictions needs to beinvestigated in future research.

7

3. Data: Overview of the HILDA Survey
Our data are drawn from the HILDA Survey which is conducted by the Melbourne
Institute of Applied Economics and Social Research, and is a broad social and economic
longitudinal survey. Since 2001, the HILDA Survey has asked Australian respondents
about their economic and subjective well-being, family structures, and labor market
dynamics. Households included in the survey were selected using a three-stage
approach. 2 First, a sample of 488 Census Collection Districts (CDs) were randomly
selected from across Australia. Second, within each of these CDs, a sample of dwellings
was selected based on expected response rates and occupancy rates. Finally, within eachdwelling, up to three households were selected to be part of the sample. In addition, thesample was replenished in Wave 11.
Although most questions in the HILDA Survey are repeated every year, there arequestions on several topics that are not repeated every year or are only asked once.
Information on the respondent’s cognitive ability has only been collected in Wave 12 of
the HILDA Survey. Wave 12 contains three measures of cognitive ability: the Backward
Digit Span (BDS); the Symbol Digits Modalities (SDM); and a 25-item version of the
National Adult Reading Test (NART25). We use BDS, SDM and NART25 scores asmeasures of the respondent’s cognitive ability. BDS is a test of working memory span
and is used in many traditional intelligence tests. After reading out longer strings ofsingle-digit numbers, the respondent is required to repeat those strings in reverse order.
The longest sequence administered is eight digits. In the BDS test, questions are divided
into eight levels, and there are two trials at each level. When the respondent’s response
for the first trial for a given level is correct, he/she is allocated a score of two for thatlevel, and then moves on to the next level. When his/her response on the first trial isincorrect, he/she moves on the second trial. If the respondent’s answer on the second trial
is correct, he/she is allocated a score of one for that level, and then moves onto the nextlevel. If his/her answer on the second trial is also incorrect, he/she is allocated a score ofzero for that level, and this test is discontinued; that is, he/she is allocated a score of zerofor all the subsequent questions. Finally, The BDS score is the sum of the scores at eachlevel, so the maximum possible score for the respondent is 16 and the minimum possible
score is zero. BDSscore denotes the respondent’s score on the BDS test. SDM is a
general test for divided attention, visual scanning and motor speed. The respondent is
Detailed information on the sample design of the HILDA Survey is available on Wooden et al.
(2002) and Watson and Wooden (2013).

28required to match symbols to numbers using a printed key. 3 SDMscore is the
respondent’s score of SDM and is defined as the number of items correctly matchedwithin a 90 second time interval. NART25 is a reading test and provides a measure of
mainly crystallized intelligence. In the NART25 test, the respondent is required tocorrectly read 25 irregularly spelled words which are listed roughly in order of difficulty.
NART25score is his/her score on the NART25 test, and is also defined as the number ofwords correctly pronounced. Definitions of these variables and the other variables usedin the analysis are provided in Appendix I.
The sample used in this paper is restricted to individuals who meet all of thefollowing criterion: (i) males and females aged 40 and over; (ii) all three scores relating
to cognitive ability are available; (iii) English is their first language; (iv) their reported
working hours are not deemed to be an outlier; and (v) information on all the relevant
variables is available. Table I shows descriptive statistics for all the variables used in theanalysis. In our sample, the maximum values of BDSscore, SDMscore, and
NART25score are 14, 104 and 24, respectively. Working hours is the respondent’s usual
hours of working per week. The mean values of Working hours for males and females
are 26.9 and 16.6, respectively.

[Table I around here]

Table II provides information on the current employment status of respondents bygender and age group. For all age groups, a higher percentage of males are working fulltime than females, and for both males and females as age rises the proportion of full-timeworkers falls.

[Table II around here]

Are these differences of working hours associated with differences in cognitive
ability? Figure 1 shows kernel density estimates of the distribution of each of the threecognitive ability measures for males and females for three groups: respondents whose
working hours are 35 hours per week or more; those whose working hours are greater
3

Strauss et al. (2006) provide details of the SDM test.

9than zero but 34 hours per week or less; and those who are not working. Panels A1 andB1 in Figure 1 show the BDS score distributions, and show that the BDS score
distributions for those who are not working are located slightly to the left of the BDS
score distributions for those who work full-time or part-time. Comparing the
distributions of the SDM score among these three groups in Panels A2 and B2, thedistributions for those who are not working are clearly located to the left of the SDM
score distributions for those who work full-time or part-time. In Panels A3 and B3, thedistributions of the NART25 scores for males and females who are not working are also
located to the left of the other NART25 score distributions.

[Figure 1 around here]

A comparison of the distributions of cognitive ability between those who work fulltime and those who work part-time suggests that there are some differences between
them. Comparing the distributions of the SDM scores for full-time and part-time maleworkers presented in Panel A2 indicates that the distribution for males who work parttime is located to the left of the distribution for males who work full-time. In contrast, theNART25 score distribution for males who work full-time is located to the left of the
NART25 score distributions for males who work part-time (in Panel A3). These
differences indicate that each measure may capture different dimensions of cognitive
ability. For females, the distribution of SDM score for full-time workers is locatedslightly to the right of the distribution of SDM score for part-time workers (in Panel B2),
while there are not clear differences between full-time work and part-time work in both
the distributions of BDS and the NART25 scores (Panels B1 and B3).
Thus, we can observe that there appears to be some differences in the locations of
the distributions of cognitive ability among the three groups (full-time, part-time and notworking). In the next section, estimation results for the impact of working hours on the
BDM, SDM and NART25 scores adjusted for the other covariates are presented,
respectively.

10

4. Estimation results
All regression results reported in this section are estimated using STATA version 13.
Table III presents estimates of the coefficients of the variables that are included inequation (2) but not equation (1), that is, the variables that are used to generate exclusion
restrictions. The estimation results in columns (1) and (2) indicate that the exclusion
restriction variables are jointly statistically significant in explaining working hours formales (F-statistics is 55.94) and females (F-statistic is 64.23). Males who receive publicbenefits excluding the Age Pension (Other public benefits) significantly reduce theirworking hours compared to males who do not receive these benefits. In column (2),while the exclusion variables which indicate the factor of labor demand are statisticallyinsignificant, Number of dependent children and Other public benefits (Work experience)
have significantly negative (positive) impacts on the hours worked by females.

[Table III around here]

Table IV reports the results of estimating equation (1) taking account of theendogeneity of working hours. After controlling for the respondent’s human capital anddemographic variables, as shown in columns (1)–(3), the coefficients of Working hourssquared are significantly negative and the coefficients of Working hours are alsosignificantly positive for males. As can be seen from the results in columns (4)–(6), thesame is true for females.

[Table IV around here]

These results indicate that, for both males and females, the magnitude of thepositive impact of working hours on their cognitive ability is decreasing until working
hours reaches a threshold, and above that, further increases in working hours have anegative impact on their cognitive functioning. As Wooden et al. (2012) point out, BDM
and SDM are measures of fluid intelligence, while NART25 is a measure of crystallized
intelligence. Crystallized intelligence tends to be maintained through occupational orcultural experiences. Assuming that hours of working are associated with the degree ofoccupational experiences, working hours per se could be regarded as cognitive repair

11activities, while investments for repair activities may result in hours of working.
Similarly, although fluid intelligence is subject to a decline as people get older, fluid
intelligence could be also maintained by working hours closer to the threshold.
Then, where is the threshold? In other word, when does the impact of working hours
on cognitive ability change from being positive to negative? In Figure 2, we calculate themagnitude of the impacts of working hours on cognitive measures after controlling forother variables, using the estimated coefficients presented in Table IV. For men thepeaks occur around 25 hours for BDS, 30 hours for SDM, and 25 hours for NART25.
For women the peaks occur a little earlier, around 22 hours for BDS, 27 hours for SDM,
and 24 hours for NART25. Moreover, Figure 2 also suggests that the cognitive ability of
those working extremely long hours can be lower than those who are not working at all.
For example, the SDM score of those who are usually 60 hours per week is lower thanthe SDM score of those who are not working both for males and females (Panel A2).
This suggests that longer working hours can lead to a deterioration of cognitive
functioning. Figure 2 suggests that as working hours increase, females reach the peakearlier, and their cognitive test scores decline faster compared to male counter parts. We
conducted tests if these visual differences are statistically significant. However, it isfound that the coefficients of working hours and working hour squares are notstatistically different between the two gender groups.

[Figure 2 around here]

The results presented in Table IV and graphed in Figure 2 indicate that there is a
non-linearity in the effects of working hours on cognitive functioning for middle aged
and older males and females living in Australia. Even after including retirees and taking
account for endogeneity and censoring of working hours, our findings are consistent with
Virtanen et al.’s (2009) findings, that is, long working hours have a negative effect on
cognition in middle age. Our results indicate that the part-time work is an effective way
to maintain cognitive functioning relative to retirement or unemployment.

12

5. Concluding remarks
We examined the causal impact of working hours on the cognitive ability of middleaged and older aged males and females living in Australia using the HILDA Survey
dataset. This study is unique in that it focuses on the intensive margin (working hours)
rather than the extensive margin (labor force participation) and investigates the optimal
working hours for middle aged and older workers. Using the test scores of memory spanand cerebral dysfunction for the respondents, it is found that working hours up to 25–30
hours per week have a positive impact on cognition for males depending on the measureand up to 22–27 hours for females. After that, working hours have a negative impact on
cognitive functioning. This indicates that the differences in working hours is an
important factor for maintaining cognitive functioning in middle and older adults. In
other words, in the middle and older age, working part-time could effective inmaintaining cognitive ability. It is worth noting that our findings did not show any
statistically significant gender differences in the effects of working hours on cognitive
functioning. Our study highlights that too much work can have adverse effects on
cognitive functioning.

[Appendix Table I around here]

13

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15

Table I: Descriptive Statistics
Male (obs.=2965)
Mean Std. Dev. Min Max
BDSscore
7.21
2.60
0
14
SDMscore
43.83
12.07
0
95
NART25score
14.56
5.23
0
24
Working hours-squared/100
12.35
12.55
0
64
Working hours
26.92
22.60
0
80
Vacancy rate
1.45
0.36
0.9 2.45
Inner regional
0.27
0.44
0
1
Outer regional
0.13
0.34
0
1
Remote
0.01
0.10
0
1
Very remote
0.00
0.04
0
1
Number of dependent children
0.59
1.02
0
7
Parent is still alive
0.51
0.50
0
1
Other public benefits
0.13
0.34
0
1
Australian citizen
0.94
0.23
0
1
Work experience
35.42
10.41
0 69.56
Ownhouse
0.82
0.39
0
1
Age-squared/100
35.16
15.08
16 88.36
Age
58.01
12.27
40
94
School years 7-10
0.45
0.50
0
1
School years 11 and over
0.53
0.50
0
1
University
0.30
0.46
0
1
Technical college
0.27
0.44
0
1
Other school
0.10
0.31
0
1
Non-indigenous origin
0.99
0.11
0
1
Married
0.67
0.47
0
1
Source: Authors' calculations using the HILDA Survey dataset.

16

Female (obs.=3502)
Mean Std. Dev. Min Max
7.23
2.53
2
14
46.41
12.74
2 104
14.70
4.82
0
24
6.21
8.79
0
64
16.60
18.59
0
80
1.43
0.35
0.9 2.45
0.28
0.45
0
1
0.11
0.32
0
1
0.01
0.10
0
1
0.00
0.04
0
1
0.52
0.94
0
7
0.50
0.50
0
1
0.18
0.38
0
1
0.95
0.21
0
1
26.10
11.80
0
68
0.81
0.39
0
1
35.85
15.70
16 10058.52
12.64
40 100
0.48
0.50
0
1
0.50
0.50
0
1
0.28
0.45
0
1
0.17
0.37
0
1
0.16
0.37
0
1
0.98
0.13
0
1
0.58
0.49
0
1

Table II: Current Employment Status by Age and Gender
Full-timePart-time Non participants/ Total Sample
35 hours and more 34 hours and less
Unemployed
Size
Male
84.1%
6.8%
9.1%
Aged 40–54
Aged 55–69
43.6%
17.1%
39.2%
Aged 70 and over
2.6%
5.7%
91.8%
Total
53.9%
10.2%
35.9%
Female
41.2%
39.3%
19.5%
Aged 40–54
Aged 55–69
21.6%
24.0%
54.4%
Aged 70 and over
0.7%
3.5%
95.8%
Total
25.8%
26.4%
47.8%
Source: Authors' calculations using data from Wave 12 of the HILDA Survey.

17

1345
1038
582
2965
1535
1233
734
3502

Table III: Models for Working Hours

Vacancy rate
Inner regional
Outer regional
RemoteVery remote
Number of dependent children
Parent is still alive
Other public benefits
Australian citizen
Work experience
Ownhouse

Male(1)
Working hours
1.038[1.125]-0.431[0.928]2.391 *
[1.347]9.285 **
[4.267]14.901 **[6.933]0.851 **
[0.396]2.747 ***
[1.045]-24.660 ***[2.100]0.170[1.600]2.037 ***
[0.139]0.257[1.124]

Female(2)
Working hours
0.552[1.322]-1.916 **[0.974]1.553[1.369]10.450[7.191]-7.754[9.368]-1.292 ***[0.461]-0.158[1.109]-19.415 ***[1.465]0.867[2.077]
1.092 ***
[0.065]-0.479[1.210]F-test H0: the coef. on these
55.94 ***
64.23 ***
variables are jointly zeroNotes:
1) *, ** and *** indicate statistical significance at the 10%, 5% and 1% levels, respectively.
2) These models are estimated by the Tobit method. Figures reported in square brackets are standard errors adjusted forheterogeneity.
3) These models also include the explanatory variables (excluding the variables related to working hours) that are reported
in Table IV. Coefficient estimates associated with these variables are not reported.

18

Table IV: Impacts of Working hours on Cognitive Skills

Working hours-squared/100
Working hours
Age-squared/100
Age
School years 7-10
School years 11 and over
University
Technical college
Other school
Non-indigenous origin
MarriedConstant
Cragg-Donald Wald F
statistic for weak instruments
Sample size
Log likelihood
F-test H0: all the coef. except
the constant are jointly zero

(1)
BDSscore

Male
(2)
(3)
SDMscore NART25score(4)
BDSscore

Female(5)(6)
SDMscore NART25score-0.206 **[0.090]0.103 **
[0.044]-0.011[0.028]-0.004[0.036]
0.638 **
[0.262]1.315 ***
[0.274]0.924 ***
[0.140]-0.095[0.123]0.286 *
[0.168]0.781 **
[0.392]0.155[0.110]5.451 ***
[1.194]-0.946 ***[0.334]0.576 ***
[0.163]-0.322 ***[0.122]0.041[0.147]5.921 ***
[1.292]10.055 ***[1.321]
3.413 ***
[0.493]0.040[0.478]1.670 **
[0.655]2.262[1.421]1.655 ***
[0.422]36.383 ***[4.717]-0.270 *[0.158]0.135 *
[0.077]-0.054[0.056]0.145 **
[0.068]3.426 ***
[0.625]6.864 ***
[0.636]3.532 ***
[0.225]0.243[0.229]0.866 ***
[0.317]1.464 **
[0.679]0.137[0.201]-0.186[2.173]-0.369 ***[0.142]0.163 ***
[0.058]-0.112 ***[0.025]0.140 ***
[0.033]0.757 **
[0.302]
1.288 ***
[0.314]0.833 ***
[0.144]-0.149[0.145]-0.050[0.137]0.346[0.322]-0.053[0.107]1.102[1.120]-1.323 **[0.534]0.704 ***
[0.219]-0.748 ***[0.100]0.522 ***
[0.128]5.305 ***
[1.308]7.925 ***
[1.347]1.533 ***
[0.540]0.376[0.548]-0.140[0.510]2.505 *
[1.385]0.811 *
[0.414]29.245 ***[4.308]-0.551 **[0.243]0.269 ***
[0.099]-0.209 ***[0.045]0.372 ***
[0.056]4.501 ***
[0.572]
6.925 ***
[0.588]3.689 ***
[0.224]
0.593 **
[0.255]0.877 ***
[0.235]1.660 ***
[0.608]-0.036[0.181]-9.130 ***[1.866]

25.22

25.22

25.22

20.31

20.31

20.31

2965
-7023

2965
-10897

2965
-8610

3502
-8395

3502
-130633502-1012130.26 ***

187.2 ***

132.5 ***

23.83 ***

223.2 ***

121.0 ***

Notes:
1) *, ** and *** indicate statistical significance at the 10%, 5% and 1% levels, respectively.
2) These models are estimated by instrumental variable estimation. Figures reported in square brackets are standard errors
adjusted for heterogeneity.
3) The Cragg-Donald Wald F statistic is computed using the "ivreg2" command in STATA 13.

19

Figure 1 : Kernel estimates of the distribution of cognitive skills by working hours
Panel B1: Backward Digit Span (BDS) (female)

0

0

.05

.05

Kernel density.1.15

Kernel density
.1
.15

.2

.2

Panel A1: Backward Digit Span (BDS) (male)

35 hours or more
Non-participants/Unemployed

35 hours or more
Non-participants/Unemployed

34 hours or less

34 hours or less.04
Kernel density
.02
.03
.01
0

0

.01

Kernel density
.02
.03

.04

.05

Panel B2: Symbol Digits Modalities (SDM) (female).05

Panel A2: Symbol Digits Modalities (SDM) (male)

15

10
5
Backward Digit Span score

0

15

10
5
Backward Digit Span score

0

0

20

40
60
Symbol Digits Modalities score

35 hours or more
Non-participants/Unemployed

80

100

0

34 hours or less

20

40
60
Symbol Digits Modalities score

35 hours or more
Non-participants/Unemployed100

34 hours or lessPanel B3: National Adult Reading Test (NART25) (female)

0

0

.02

.02

Kernel density.04

Kernel density
.04
.06

.06

.08

.1

.08

Panel A3: National Adult Reading Test (NART25) (male)

80

0

5

10
15
National Adult Reading Test score

35 hours or more
Non-participants/Unemployed

20

25

0

34 hours or less

5

10
15
National Adult Reading Test score

35 hours or more
Non-participants/Unemployed

Source: Authors' calculations using the HILDA Survey wave 12.

2020
34 hours or less25

Figure 2 : Estimated impacts of working hours on cognitive skills
Panel A1: Backward Digit Span (BDS)

Panel A2: Symbol Digits Modalities (SDM)

score

score

9

55

6

45

3

35

0

25
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Working hours

Working hours

male

femalemale

femalePanel A3: National Adult Reading Test (NART)

score
20
17
14
11
8
5
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70

Working hours
male

femaleNote: The fitted values of these scores are computed using the estimated coefficients reported in Table IV where all variables except
Working hours-squared/100 and Working hours are evaluated at their sample mean values.

21Appendix I: Definitions of Variables
Name

SDMscore

Definition
The question consists of eight levels. At each level the respondent has a maximum of two
trials. When the respondent gets the answer correct on the first trial he/she is awarded ascore of two, and moves on to the next level. When the respondent's answer on the firsttrial is incorrect, he/she moves onto the second trial. If his/her response on the second trial
is correct, he/she is awarded a score of one and moves on to the next level. When both
his/her responses at the same level are incorrect, he/she is awarded a score of zero and thistest is finished at that point. The sum of the scores at each level is the BDS score.
The number of items correctly matched within a 90 second time interval.

NART25score

The number of words the respondent correctly pronounces.

Working hours-squared/100(Working hours)2/100
The number of usual or average working hours per week the respondent works.

BDSscore

Working hours
Vacancy rate

Inner regional(Job vacancy/Employed)*100, where Job vacancy denotes the number of job vacancies inthe state where the respondent lives in November 2012 which are reported by theAustralian Bureau of Statistics (ABS), and Employed denotes the number of total
employed persons in the relevant state in November 2012 which are reported by the
0-1 dummy variable taking the value unity if the respondent lives in inner regional
Australia, and 0 otherwise.

Outer regional

0-1 dummy variable taking the value unity if the respondent lives in outer regional
Australia, and 0 otherwise.

Remote0-1 dummy variable taking the value unity if the respondent lives in remote Australia, and0 otherwise.

Very remote

0-1 dummy variable taking the value unity if the respondent lives in very remote
Australia, and 0 otherwise.

Number of dependent children

The number of the respondents' children who reside with the parent or guardian, and whoare aged under 15 years or aged 16–24 years and enrolled in full-time education.

Parent is still alive

0-1 dummy variable taking the value unity if either the respondent's father or his/hermother still alive, and 0 otherwise.

Other public benefits

0-1 dummy variable taking the value unity if the respondent receives any income from thegovernment in the form of a benefit, pension or allowance except the age pension , and 0
otherwise.
0-1 dummy variable taking the value unity if the respondent is an Australian citizen, and0 otherwise.

Australian citizen
Work experience

Total years the respondent is (was) in paid work

Ownhouse

0-1 dummy variable taking the value unity if the respondent owns his/her own house or iscurrently paying off a mortgage, and 0 otherwise.

Age-squared/100(The squared of Age)/100

Age

Squared of Respondent's age in years at the time of the survey

School years 7-10
(benchmark: the respondent's highest years ofschool completed are under 7)
School years 11 and over(benchmark: the respondent's highest years ofschool completed are under 7)

0-1 dummy variable taking the value unity if the respondent's highest years of school
completed are between 7 and 10, and 0 otherwise.

University(benchmark: the respondent did not obtain
post-school qualification)
Technical college(benchmark: the respondent did not obtain
post-school qualification)
Other school(benchmark: the respondent did not obtain
post-school qualification)
Non-indigenous origin

0-1 dummy variable taking the value unity if an educational institution where therespondent obtained his/her highest post-school qualification is a University, Teachers'college/College of Advanced Education, Institute of Technology, and 0 otherwise.
0-1 dummy variable taking the value unity if an educational institution where therespondent obtained highest post-school qualification is Technical college/TAFE/College
of Technical and Further Education , and 0 otherwise.
0-1 dummy variable taking the value unity if an educational institution where therespondent obtained highest post-school qualification is other organizations, and 0
otherwise.
0-1 dummy variable taking the value unity if the respondent is not of Aboriginal or
Torres Strait Islander origin, and 0 otherwise.

Married0-1 dummy variable taking the value unity if the respondent is currently married, and 0
otherwise.

0-1 dummy variable taking the value unity if the respondent's highest years of school
completed are 11 and over, and 0 otherwise.

22