電気学会論文誌 C（電子・情報・システム部門誌）
IEEJ Transactions on Electronics, Information and Systems
Vol.133 No.1 pp.61-66
DOI: 10.1541/ieejeiss.133.61

Paper
Estimates of Subjective Age Based on the Facial Images of Others:
Comparative Studies of Koreans and the Japanese
Masato Konishi＊ Non-member,
Noriko Nagata＊a) Member,

Yasuhiro Azuma＊ Non-member
Young-suk Shin＊＊ Non-member(Manuscript received April 13, 2012, revised Sep. 6, 2012)
We designed a method for estimating the subjective age of a person. Using this method, one evaluates one’s own age by
estimating whether a person shown in a facial image looks older or younger than oneself. Thus far, experiments have shown thatJapanese and Americans tend to underestimate their subjective ages. In this study, we conducted estimation experiments
involving subjects who were racially Japanese ― some of whom were from Japan and others who were raised in the Korean
culture ― and investigated the differences between the two groups’ results. Experiments were performed in which Koreanparticipants viewed Korean and Japanese facial images, and the Japanese participants also viewed Korean facial images. Throughthese experiments, it was confirmed that the bias values of the subjective ages were negative, indicating that a younger
self-identity occurs despite differences in Japanese and Korean societies and cultures.
Keywords : facial images, subjective age, non-liner regression analysis

and facial images. These results suggested that the tendency
toward a younger identity was influenced by misleading memoriesof their own facial images and socio-psychological factors.
However, it was not clarified which factors (e.g., nationality andculture or race) related to the young identity.
It is believed that investigating the psychological features ofsubjective age may be useful for improving the design of systems
for the human interface and human system interaction fields. For
instance, designing agents’ behavior (such as manner of expressing
courtesies) is one of the more important issues in the developmentof various agent systems such as self-development and client
services. Findings concerning “objectivization of subjectivity”
such as subjective age bias can be applied to the evaluations ofemotions and feelings in many fields.
In this study, we conducted estimation experiments involving
Koreans belonging to the same race as the Japanese but having a
different culture, and we investigated the differences between the
two. Experiments were performed in which Korean participants
viewed Korean and Japanese facial images; in addition, theJapanese participants viewed Korean facial images. This experiment
investigated the effects of differences in nationality (culture orrace).

1. Introduction
When individuals engage in communication, they tend to makejudgments about the attributes (e.g., age, gender, ethnicity, social
status, or professional background) of those with whom they
communicate based on appearance(1)(2). When forming attitudes
during social interactions, age is one of the most important factors;
first impressions are often significantly influenced by the fact thatthose with whom we communicate are older or younger than weare. Individuals tend to unconsciously estimate the ages of thosearound them on the basis of appearance and then use this toestablish the appropriate attitude and language to adopt.
Nevertheless, studies suggested that these judgments are often
inaccurate; there are often instances when individuals overestimate
the ages of those with whom they communicate in the belief thatthe people are much older than themselves.
People generally tend to overestimate the ages of other people.
In this study, we assumed that people did not really estimate theages of other people incorrectly; instead, they simply foundthemselves to appear younger or older than they really were(1)(3)(4).
We rated the ability of participants to estimate a person’s relative
age based on whether they estimated people in facial images
shown to them as well as people they communicated with face toface to be older or younger than themselves. We calculated“subjective age” from the obtained distribution data.
Thus, we observed that subjective ages, in the case of theJapanese, were generally lower than the actual ages. American
males, on the contrary, did not exhibit a tendency to underestimate
their ages. The underestimation of age occurred despite differencesin the Japanese and American participants’ nationalities, cultures,

2. Previous Works
Numerous studies explored age estimation using faces(5)-(13). In
particular, much of the research focused on automatic age
estimation by computer(5)(14). The applications of this technology
have recently been extended to a variety of fields including
biometrics, security, and digital consumer electronics. However,
because of the particularity and complexity of faces, various
technical issues with automatic age estimation remain that relate
to sociology and psychology as well as the biological or
anthropometric perspective(15)(16).
One of the most significant results to emerge from these studies
is “subjective age bias,” where individuals tended to overestimatea) Correspondence to: Noriko Nagata. E-mail: nagata@kwansei.ac.jp＊
School of Science and Technology, Kwansei Gakuin University
2-1, Gakuen, Sanda, Hyogo 669-1337, Japan＊＊
Department of Information and Communication engineering,
Chosun University
375, Seosuk-dong, Dong-gu, Gwangju 501-759, Korea© 2013 The Institute of Electrical Engineers of Japan.

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Estimates of Subjective Age: Koreans and the Japanese (Masato Konishi et al.)than did females.
The subjective ages were obtained by estimating the actual agesof other people whom the participants considered to be of thesame age by rating whether they perceived the subjects as older oryounger. These subjective ages were described as “relative
imaginary ages”. Moreover, we found that the subjective ages
remained the same regardless of stimulus expression, gender, orage group. Using the results stated above, we were able to narrow
down the factors responsible for the underestimation of one’s own
age to the following two factors from the original four factors(4).
─ Memory may be misleading, and people may not remember
the most recent image of themselves. In face-to-facecommunication, other people’s images are always current,
but our own facial image needs to be remembered.
─ As Barak and Stern made clear, there seems to be a link
between age and socio-psychological parameters; forexample, confidence and social rank of an individual are
related to other people’s perceptions of their age.
With regard to subjective age, we cannot separately observe thetwo perceptions of participants that they are younger than theiractual age and that other people are older than themselves at thepresent time. Because the two factors mentioned above supported
the perception of participants that they are younger than theiractual age, in this study, we assumed that this perception is true;
however, we did not discredit the perception of participants that
other people are older than themselves.
In this study, we conducted estimation experiments using
Korean participants to investigate the effects of cultural and racial
factors that could not be distinguished in the comparative study
between the Japanese and the Americans.

the ages of the facial images of others. Although the tendency toperceive another person’s face as older was often pointed out invarious areas, it was not an intended topic of the research(7)-(9).
We focused on the tendency of claiming younger identity andassumed that the perception that participants viewed other people
as older than their actual ages was because of the perception thatparticipants felt themselves younger than their actual ages. In ourprevious study, we processed data obtained from relative age
estimation, such as the classification of other people by participants
as older or younger than themselves, using nonlinear regression
analysis and then calculated the subjective age of each participant.
Thus, we could apply the bias value of the subjective age ofeach participant to ANOVA and observe the relationship between
the subjective age and the profile (gender and age group). The
ANOVA analysis revealed that Japanese and Americans tended toperceive themselves as younger (i.e., perceive other people asolder), as shown in Figures 1 and 2. Moreover, when we considered
age perception on the basis of profile differences, Japanese males
tended to underestimate their ages to a greater extent than did
Japanese females. The tendency to underestimate age was strongest
in the age group 25 – 34. The older the participants were, the closer
the subjective ages were to the real ages. In addition, American
males did not exhibit a strong tendency to underestimate age,unlike Japanese males(4).
The scale used to determine the bias values of the subjective
ages in Figure 2 is entirely different from that used traditionally;that is, the subjective ages of young people were lowest, andmales tended to underestimate their own ages to a greater extent

3. Subjective Age Estimation Using Facial Images
3.1 Experimental Stimuli
Facial images of both
Koreans and Japanese aged between 20 and 59 years were used as
experimental stimuli, and the number of male and female images
was almost equal. These images were divided into eight classes
for each gender, and each class included more than five facial
images. Figure 3 shows examples of the facial images. Each facial
image was saved as a high-resolution color digital image having a
resolution of 300 × 350 pixels. To easily collect the facial images,
no special conditions for shooting, lighting, makeup or hairstyles
were set; this policy is consistent with the collection of facial
images in our previous research.

Fig. 1. Bias values of subjective age (Japanese andAmerican).

(a) Korean(b) JapaneseFig. 2.

Fig. 3. Examples of facial images (Class: 25–29 years).
(We have obtained individuals’ permissions to publish
these photographs).

Bias values of subjective age (age class).
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IEEJ Trans. EIS, Vol.133, No.1, 2013

Estimates of Subjective Age: Koreans and the Japanese (Masato Konishi et al.)Table 1. Statistics associated with the experiments.
(‘M’, ‘SD’ and ‘N’ represent mean of the bias valuesof subjective age, standard deviation, and the numberof participants, respectively).

3.2 Rating Experiment
For both male and female
participants belonging to different age and gender groups, weselected facial images from their own age classes as well as thenext younger and older classes. For example, for a 32-year-old
male participant, 5 male and 5 female images were selected fromthe same age class (30 – 34) and from the next younger (25 – 29)
and older (35 –39) classes. Therefore, the total number of facial
images used was 30 (5 images/class × 3 classes × 2 genders).
Next, we experimented with a rating scale for the facial images
used as stimuli. The participants were shown random facial
images on the computer monitor, and they evaluated whether each
person shown in the image looked older or younger than themselves.
The evaluation had 5 ranks: “Definitely older than myself (2)”,“Probably older than myself (1)”, “Not able to estimate (0)”,“Probably younger than myself ( − 1)”, and “Definitely younger
than myself ( − 2)”. Then, we limited the facial images to only
people around the same ages in order to raise the efficiency of theexperiments.
We defined the three experiments in this study as follows:[Experiment I] Experiments on Korean subjects using facial
images of Koreans[Experiment II] Experiments on Korean subjects using facial
images of Japanese[Experiment III] Experiments on Japanese subjects using facial
images of Koreans
3.3 Participants
112 Koreans (male: 60, female: 52)
participated in experiment I, 93 Koreans (male: 48, female: 45)
participated in experiment II, and 135 Japanese (male: 69, female:66) participated in experiment III. All participants were between
25 and 54 years old. Table 1 shows the statistics associated withthe experiments.
3.4 Subjective Age Quantification
Figure 4 depicts theconcept of subjective age, as discussed in this paper, and how it iscalculated on the basis of whether participants assessed the facesof other people depicted in images as looking older or younger
than themselves. From these results, we obtained data regarding
the “difference in actual age between participants and others” and“participant estimation regarding the age of others”. We plotted
these results on a two-dimensional plane with the x-axis as thedifference in actual age and the y-axis as the estimation result. The
data lying in the positive area should be plotted in the positive
sphere, and the data lying in the negative area should be plotted in
the negative sphere; thus, the graph is supposed to give a right/up
and left/down curve, and the center of the graph is supposed to belocated near the origin of the x-axis. Here, if the participantstended to judge the people shown in the facial images as younger
than their real ages, the entire distribution of the data shifts toward
the right (in the positive area). Conversely, if the participant’s tend
to judge the people shown in the facial images as older than theirreal ages, the entire distribution of the data shifts toward the left(the negative area). The shifting of the distribution toward thepositive/negative area would indicate the participants’ tendency tosignificantly underestimate/overestimate the ages of others. We
assumed that one of the factors behind this tendency was that eachparticipant’s subjective age was often more or less than his/her
real age. Specifically, we calculated a gap between the center ofthe distribution and the origin of the coordinate for the x-axis anddefined this gap as the bias value of subjective age; thus, subjective
age can be calculated by adding the bias value to the participant’s
actual age.

(a) Experiment I (Participants: Korean, Facial images: Korean)(b) Experiment II (Participants: Korean, Facial images: Japanese)(c) Experiment III (Participants: Japanese, Facial images: Korean)Fig. 4. The concept of subjective age. The x-axis is thedifference between the actual age of the participant andthe actual age of the facial images. The y-axis is the rating
value. A distribution centered in the negative part of thegraph would indicate that a participant tended to perceive
the younger facial images as about his/her own age.
Subjective ages were calculated in order to quantify the resultsof the rating experiments. When we plotted the results on a
two-dimensional plane with the x-axis as the relative age (difference
between the chronological ages of the person whose facial image
was shown and the subject) and the y-axis as the estimation result,
we obtained an upper-right distribution. This distribution indicatedthat the certainty factor for selecting “Definitely older than myself(2)” increased as the other person’s age increased. Since this63

IEEJ Trans. EIS, Vol.133, No.1, 2013

Estimates of Subjective Age: Koreans and the Japanese (Masato Konishi et al.)Fig. 5. Estimation curves for 18 female individuals in
the middle age group with a neutral expression.

Fig. 6. Bias values of subjective age (Japanese andKorean).

distribution converged at rating values of 2 (Definitely older) and− 2 (Definitely younger) and increased monotonically, we assumed
that this distribution was approximated by a logistic function andhence applied nonlinear regression analysis to the distribution foreach participant. Figure 5 shows an example of the estimation
curves from 18 female individuals from the middle age group witha neutral expression.
Here, the logistic function, which converged at a rating value of± 2, was defined by the following mathematical formula:of nationality was highly statistically significant (F [1, 259] = 18.44,
p < .01). There were also significant differences between
experiment I and experiment III and between experiment II andthe previous work (F [1, 191] = 4.96, p < .05, F [1, 251] = 11.81,
p < .01).
In addition, we performed a two-way ANOVA using gender andnationality as independent variables. This analysis revealed asignificant interaction between gender and nationality inexperiment I and the previous work (F [1, 254] = 6.97, p < .05). A
simple main effect test was conducted on the interaction between
gender and nationality, and a significant difference between Korean
females and Japanese females was confirmed (F [1, 259] = 21.31,
p < .01). There was also a significant interaction between genderand nationality in experiment III and in the previous work
(F [1, 288] = 4.00, p < .05). A simple main effect test was also
conducted on the interaction between gender and nationality,
showing no significant difference in Japanese males but asignificant difference between Korean and Japanese facial images(F [1, 288] = 8.30, p < .01).
4.2 Experiment I
Table 1a and Figure 7a show theexperimental results of experiment I (participants: Korean; facial
images: Korean). A two-way ANOVA was performed, using
gender and age group as independent variables and the bias valueof subjective age b as the dependent variable. This analysis
revealed that the main effects of each gender and age group were
insignificant.
4.3 Experiment II Table 1b and Figure 7b show theexperimental results of experiment II (participants: Korean; facial
images: Japanese). A two-way ANOVA was performed using
gender and age group as independent variables. This analysis
revealed that the main effect of age group was significant(F [2, 69] = 9.86, p < .01), and a significant interaction did notexist between gender and age group (F [2, 69] = 0.54, n.s.). In
addition, Tukey’s HSD test was performed for age group,
confirming a significant 10% difference between young (25 – 34)
and young-middle (35 – 44) and a 1% difference between young(25 – 34) and middle (45 – 54).
4.4 Experiment III
Table 1c and Figure 7c show theexperimental results of experiment III (participants: Japanese;
facial images: Korean). A two-way ANOVA was performed using
gender and age group as independent variables and the bias valuey=4− 2 ............................................ (1)1 + exp ( − a ( x − b) )where a is the slope of the curve and b the zero crossing point in
the approximation curve with the x-axis, a and b were estimatedby a nonlinear regression analysis; we defined b as “the bias valueof the subjective age” and the addition of the bias value to theactual age as “the subjective age”. In the case of Figure 4, if thevalues of a and b were 0.35 and − 3.12, respectively, the bias valueof the subjective age of a participant was − 3.12. This implies that
this participant perceived himself/herself as 3.12 years younger
than his/her actual age. After the bias values of the subjective age
were calculated on the basis of the data obtained from eachparticipant, these values were categorized into six groups on thebasis of gender (male and female) and age groups (25 – 34, 35 –44,
and 45 – 54). We eliminated data in which multiple coefficients ofdetermination of the regression curve approximated for eachparticipant were extremely low (R2 < 0.10) and finally processeddata of 83, 75, and 112 individuals in experiments I, II, and III,
respectively.

4. Result4.1 Summary Results
Figure 6 shows a comparison of
the average bias values of the subjective ages in the experimental
results of experiment I (participants: Korean; facial images: Korean),experiment II (participants: Korean; facial images: Japanese),experiment III (participants: Japanese; facial images: Korean), andthe previous work (participants: Japanese; facial images: Japanese).
It was confirmed that the subjective ages were generally in thenegative region in all experiments.
An ANOVA was performed between experiments using
nationality as an independent variable; it showed that the influence
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IEEJ Trans. EIS, Vol.133, No.1, 2013

Estimates of Subjective Age: Koreans and the Japanese (Masato Konishi et al.)Japanese females. These results indicated the possibility ofdifferences in the cultural environments surrounding Korean andJapanese females (e.g., social status or expected attitude).
There was also no age-group dependence in subjective age
regarding facial images of a different nationality in Experiment II.
Conversely, there was an age group dependence in subjective ages
for those of a different nationality in Experiment III. This indicateda possible difference in “look age” between Koreans and Japanese;
this may be a cultural effect on age estimation.

6. Conclusions(a) Experiment I(Participants: Korean,Facial images: Korean)(b) Experiment II(Participants: Korean,Facial images: Japanese)(c) Experiment III(Participants: Japanese,
Facial images: Korean)(d) Previous Work(Participants: Japanese,
Facial images: Japanese)

Fig. 7.

In this study, we compared the results of subjective age
estimation by Korean and Japanese participants and investigatedfactors determining the tendency to underestimate one’s own age.
The results of this study showed that (1) Koreans also tend
toward underestimation, which indicates that subjective ages
generally tend toward the negative direction despite nationality orrace; (2) the tendency toward a younger identity was significantly
stronger for Koreans than for Japanese; and (3) there are probably
cultural effects on the tendency toward a younger identity.
The accuracy of age estimation or face recognition can be
improved by investigating psychological features of participants
through facial studies and human-machine interactions. Besides,
the subjective age is self-image; thus, by finding the mechanism of
self-image, we can use the concept of subjective age in thedevelopment of various socio-psychological applications such as
self-development and client services. In addition, discussions
regarding cultural effects such as comparison of subjective ages at
an international level are useful in achieving breakthroughs inmechanisms of a variety of other psychological measures.
Particularly, these discussions are expected to be useful in studies
regarding the “objectification of subjectivity” such as subjective
time and distance estimations.
In the future, we intend to investigate circumstantial factors
such as the ability of participants to remember their own facial
images because subjective ages tended toward the negative
direction despite differences in nationalities and cultures. Moreover,
we will investigate the underestimation of age in other age groups,
separately observe the perception of oneself as younger and others
as older, and determine the effect of makeup on the objective ages
(ages estimated by others) of females.

Bias values of subjective age.

of subjective age b as the dependent variable. This analysis revealed
that the main effects of gender and age group were insignificant.

5. Discussion
5.1 Universality of the Younger Identity
First, weinvestigated the universal factors influencing the tendency tounderestimate one’s own age. Using the above results, it was
confirmed that the bias value of subjective age generally tends
toward the negative direction despite differences in nationalities
and cultures of participants and their facial images. It is suggested
that remembering one’s own facial image may be a factor
influencing this tendency despite differences in nationality andculture. Estimating one’s own age (or that of another known
person) involves remembering previous facial images. However,when estimating the ages of strangers, only currently observed
information is available. We suggest that when we can estimate
our real age, our remembered image tends toward the previous
direction; this gap causes us to perceive others as older than they
actually are. Factors influencing the participants could include
remembering one’s own facial image and socio-psychologicaleffects. The relationship between the two factors or the separationand extraction of the factors will be studied in the future. In
addition, to obtain more-accurate results, it is necessary to increase
the number of participants.
5.2 Summary Results
Next, we investigated theunderestimation of age from the viewpoint of socio-psychologicalfactors. Experiment I revealed that the tendency toward a younger
identity was stronger for Koreans than for Japanese. In particular,
subjective ages were notably lower for Korean females than for

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Masato Konishi

Yasuhiro Azuma(Non-member) received the BS and MS degrees in
informatics from Kwansei Gakuin University in2009 and 2011, respectively. His research interests
include affective computing and the psychology offace perception.

Noriko Nagata(Member) received the BS degree in mathematics
from Kyoto University in 1983 and the PhD degree
in systems engineering from Osaka University in
1996. She was a researcher of the Industrial
Electronics and Systems Laboratory in Mitsubishi
Electric Corporation from 1983 to 2003. She joined
Kwansei Gakuin University in 2003, where she iscurrently a professor. In 2009, she was a visiting
scholar at Purdue University. Her research interests include machine vision,
media engineering, and affective computing. She is a member of IPSJ,IEEJ, JFACE, IEEE, and ACM.
Young-suk Shin

(Non-member) is an associate professor in
Department of Information and Communication
Engineering, Chosun University. She received the
Ph.D. degree in computer science from Yonsei
University, Seoul, in 2001. Her research interests
include pattern recognition, biometrics, cognitivemodeling, facial expression recognition, emotion
recognition, virtual reality, and human-computerinteraction. From 2008 to 2009, she visited the Distributed & Collaborative
Virtual Environments Research Laboratory at the University of Ottawa,
Canada.

(Non-member) received the BS degree in
informatics from Kwansei Gakuin University. He iscurrently a first year MS student in Science andTechnology courses, Kwansei Gakuin University.
His research interests include affective computing
and the psychology of face perception.

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