社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

原著

How Well the Elderly Evaluate the Readability of E-paper Devices:Standardization of Minimum Legible Character Size
高齢者は電子ペーパー機器をどのくらい読みやすいと評価しているか？
---- 最小可読文字サイズの標準化について
R. Paul Lege1), Shigusa Matsunami1), Takehito Kojima2), Satoshi Hasegawa3), Masaru Miyao1)
1) Nagoya University
2) Chubu-Gakuin University3) Nagoya Bunri University

Abstract
Electronic Paper Displays (EPD) are similar to conventional paper and recently widely introduced to e-books.
And backlit Liquid Crystal Displays (LCD) has been popular for long years. Although the readability of LCDs
were studied well, that of EPD has not been fully investigated. In this experiment, we asked different age groupsof participants to evaluate the effects of font sizes of two different e-book devices (EPD: Kindle Voyage and LCD:Apple iPad) on the readability. We set the text character sizes at four levels; 4 pt (character height: 1.4 mm), 6 pt (2mm), 8 pt (2.75 mm), and 12 pt (3.25 mm). The study measured reading speed, correct answer rate and a subjective
evaluation. Our study found that those under 64 years of age could maintain their performance of readability when
the fonts were 6 pt size or higher. Those participants over 65 years of age could sufficiently read at the 8 pt fontsize. The participants found that the readability of the both E-books was equal to the performance of each otherand also equal to paper text. Therefore, E-paper display designed to function similar to paper can contribute toimproving readability, especially for the elderly. On the basis of this study, we recommend a default setting higher
than 8 pt (2.75 mm) should be displayed on the screens of E-papers.
抄録
電子ペーパー・ディスプレイ（EPD）は従来の紙とよく似ており、近年電子書籍に広く導入されている。また、バッ
クライト型液晶ディスプレイ（LCD）は、以前から電子書籍などに広く利用されてきた。ここで、液晶ディスプレ
イの可読性に関しては多くの研究が発表されているが、電子ペーパーの可読性についての研究は未だ不充分である。
本研究では、種々の年令層を含む実験参加者によって、２種の電子書籍（Kindle Voyage と Apple iPad）における、４種の文字サイズの可読性への影響を評価させた。設定した４種の文字サイズは、4 pt（文字高：1.4 mm）、6 pt（2mm）、8 pt（2.75 mm）、および 12 pt（3.25 mm）であった。実験では、読みスピード、正答率、および読みやすさの主観評価が計測された。実験結果から、64 歳以下では文字サイズが 6 pt 以上ならば読みやすいことが判明した。
他方、65 歳以上の高齢者では、文字サイズが 8 pt 以上ならば読みやすかった。今回の実験で、２種の電子書籍、及び従来の紙のどれもが、ほぼ同様に読みやすいことがわかった。電子ペーパーは、紙とよく似ているが、とくに高齢者に対しては、画面を拡大することができるので読みやすい。本研究の結果から、電子ペーパーに表示する文字
サイズに、8 pt（2.75mm）の文字高を標準として推奨する。
Keywords: Readability of E-paper, Font Sizes, Aging, Standards
キーワード：電子ペーパーの可読性、文字サイズ、加齢、標準化－ 79 －

社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

1 Introduction

four general groups according to their age: young (29At present, manufacturers of e-paper devices are

years and younger), middle-aged (30 to 44 years old),

striving to improve the visual performance of theirsenior middle-aged (45 to 64 years old), and elderly (65products to be equal to or better than conventional

years and older).

1)paper . Technically, electronic paper display (EPD,

Table 1. Participants divided by age groups

such as a Kindle Voyage) uses E-ink. E-ink is
consisted of black and white particulates through aYoung

Middle20

17

SeniorMiddleprocess of electrophoretic display, while a device suchExp.

as an iPad uses a Liquid Crystal Display (LCD)2). Bothdevices have their advantages and disadvantages

Youngfrom e-books. The interest in e-books is growing andMean㫧S.D

appears to be expanding for all ages, but questions

Exp.

have arisen regarding their functionality relative

character size and to obtain such standard.
In this study, participants of different ages took asilent reading test and then evaluated the readability
four different font sizes used on two electronic
devices (Kindle Voyage and Apple iPad). The
experiment looked at the reading performance of theparticipants for each of the four font sizes (4, 6, 8, 12
points). By testing to see if there was a significant
decrease in reading speed and the correct answer
rates with the font sizes, the aim was to uncover thewhat degree these devices matched the functionalityof conventional paper text.

80

MiddleSenior Middle
Mean㫧S.D

Mean㫧S.D

42.5㫧10.0

70.7㫧17.4

98.5㫧30.1

Elderly
Mean㫧S.D
162.1㫧43.7

We measured the cataract cloudiness of each of
the readers with an Anterior Eye Segment Analysis
System (NIDEK EAS-1000). Table 2 shows themeasured values of the readers divided into theirrespective age groups. The youngest group had
sufficient amplitude of lens accommodation. The
middle-aged group had sufficient near vision ability,
although their accommodation was slightly weaker.
The senior middle-aged group had mild presbyopia
and problems in near vision work. The elderly group
had typical presbyopia and generally had to wear
glasses for close vision.

2.2

minimum readable font size for each of the various
age groups. In addition, we wished to evaluate to15

̐The range of cloudiness gradation is 0 to 255.

to conventional paper. The aim of this study was
the two devices and to estimate minimum legible

Total

Table 2. Participant lens cloudinessparticularly with regard to long term reading such as

to compare the readability of different font sizes on

28

Elderly

Experimental design

In this experiment, we also employed three typesof devices, an e-paper (Amazon Kindle VoyageTM),
a backlit LCD (Apple iPadTM), and as a reference,
conventional paper text (with the text printed on
PPC paper of 69 % whiteness)3,4). Table 3 shows the

2 Methods

technical specifications for each of the display devices.

2.1 Participants
The readers for this experiment include 80 males
and females between the ages of 14 and 79 years (M46.7, SD 17.9). Participants who usually wore glasses
or contact lenses used them for the experiments.

In short, we refer to the Kindle Voyage as KV, theApple iPad as iPad, and the conventional paper as
simply Paper.
Table 3. Device specifications
Kindle Voyage

The experiment received approval from the Ethical
Review Board of the Graduate School of Information
Science at Nagoya University after we obtained

iPad

Paper

Screen size

6 inch9.7 inch

6 inchResolution

300 ppi

264 ppi

1200dp

In order to alleviate the possibility of reader bias

informed consent from all the participants.
Table 1 shows the number of participants divided

from brand recognition, the participants read theinto age groups. The participants were divided into

different texts from a bezel covered with white Kent

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社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

paper with only the screen showing. The test media

The participants sat in a cubicle that had aor test paper was mounted on the center of a board.

compartmental lighting system placed on a desk in a

The text displayed for each medium was set at thedarkened room (Figure 3). This experiment followedsame height. The front light level of the KV and thethe lightning system created in a previous study

back light level of the iPad were set to maximum

in order to be consistent 5,6). The headrest for thelevels. The text color was black/dark, and theparticipant’s forehead was kept at a visual distance of

background color was white/bright.

400 mm. The participants looked at the devices at an

Figure 1 shows the screen luminance for eachdevice. As expected, the screen luminance for theangle of about 100 degrees to eliminate any problems
with self-reflection.

KV showed similar results to conventional paper. In

The experiment was conducted at an illuminanceaddition, we calculated the contrast ratios from thelevel of 1,000 lx using a 6500 K LED light source

measured values of the brightness of the backgroundwith a fluorescent lamp that had a uniform color

color and text color (Figure 2). The iPad had a higher

temperature. The International Organization ofcontrast ratio compared to the other devices because

Standards (ISO) recommends an illuminance level of

it showed a lower screen luminance of black/dark

1,000 lx for doing precision work in an office7).

and a higher screen luminance of white/bright.

Fluorescent light 䊶LED
Diffuser60
0m

Head rest100°㪋㪇㪇㩷㫄㫄㩷
30°
Device50°

600 mmFigure
1.The
Thescreen
screenluminance
withlettersblackandletters and white backgroundFigure 1.
luminancewith black
white backgroundFigure 3. The setup for reading

2.2 Task design

Figure 2. The contrast ratio of each device

The display format conformed to that used forevaluation of electronic display devices by the－ 81 －

社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

International Organization for Standardization (ISO)8).

the participant’s total values in order to standardize

The experimental task was a block reading test

the performance of all the readers. A high-scoringof a short duration (Figure 4). We used random

reading time index meant that it took the participantalphanumeric text and unified the size of thea long time to complete a task. The high scoring

characters. The font type was Courier for bothcorrect answer rate index indicated that there was aexperiments because it is a uniform monospaced fontlarge number of correct answers.

that has a slight serif (“bearded”). A monospaced

After each reading, the participants also evaluatedfont is one with a fixed width; that is, each letters

the readability of the texts using a Visual Analog

occupies the same amount of horizontal space9).

Scale (VAS). We converted the values of the VAS
into a 100-point scale in the final analysis. Figure 5
provides an example of a subjective evaluation using
the VAS method. A high-score on the VAS signified
that a participant found a device to be very readable.
In terms of the scale, a score of zero could result
from extreme difficult to read or for missing values
such as when the reading time or answer rate could
not be scored.

1000㪅㪭㪼㫉㫐㩷
㫌㫅㫉㪼㪸㪻㪸㪹㫃㪼

71

㪭㪼㫉㫐㩷
㫉㪼㪸㪻㪸㪹㫃㪼

㪧㫉㪼㫋㫋㫐㩷㪾㫆㫆㪻㩷

Figure 4. Example of text block for the reading task

39As the width of the characters for Courier isuniform, our focus was with the height of the font㪧㫆㫆㫉㩷

Figure 5. Example of evaluations by VAS

size. The font sizes were set at 4 pt (approx. 1.5 mm
height), 6 pt (2 mm), 8 pt (2.75 mm), and 12 pt (3.25

We used a two-way analysis of variance (two-waymm). Figure 4 shows the example of the text blocks

ANOVA) as a statistical method to evaluate the final

for the reading task. The participants performed

results between the reading time, correct responses

twelve separate reading tests (four fonts per eachand the subjective evaluations. In addition, we alsoof three devices). We had participants read the text

used a one-way analysis of variance (ANOVA) andsilently from the top left and then we measured for

the Scheffé multiple comparison procedure in order

speed and correct answer rate.

to comprehend the importance of the different age

The participants were asked to count the number

groups.

of capital letter“M ”s in the total text with a counteras they read through the characters. We calculated

3 Results

the correct answer rate from the number of“M ”sTable 4 shows the results from the two-way

that the participants found and the actual number of

ANOVA for the participants’ evaluation (VAS),

these letters in the text. The correct answer rate wasreading time index, and correct answer rate index.

not entirely exact because the participants sometimes

The VAS, reading time index, and correct answer

misread other alpha characters as large“M ”s.

rate index showed significant differences between the

The reading time index and correct answer rateindex were divided by the average values of each of

font sizes (p<0.01), but no significant differences wereobserved among the types of devices.

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社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

Table 5. Multiple comparison for the VAS, reading time
Table 5. Multiple comparison for the VAS, reading time index, and correct ans
index, and correct answer rate index

Table 4. Two-way ANOVA for the VAS, reading timeindex and correct answer rate index
SourceVAS
㩷 Type ofdevice(D)㩷 Charactersize(C)
㩷 D×C

Df

SS

㩷
㩷

F

MS

a**,

2

470.401.33

3 504425.46 168141.82

474.426940.791511.56251.93† **; p<0.01

a**,Correct answer
rate index(Mean㫧S.D.)a**,

4 pt 12.2 㫧 12.4 b**, 1.112 㫧0.189 b**, 0.795 㫧 0.301 b**,
**

c**

c**

c**

a**,

a**,

a**,

6 pt 36.4 㫧 19.9 d**, 1.077 㫧0.179 d**, 1.011 㫧 0.162 d*,
e**

0.71

b**,

Reading timeindex
㩷 Type ofdevice(D)㩷 Charactersize(C)㩷 D×C
Correct
answer rateindex
㩷 Type ofdevice(D)㩷 Charactersize(C)㩷 D×C

Reading time
index
(Mean㫧S.D.)

VAS(Mean㫧S.D.)

e**

e**

b**,

b**,

c**,

c**,

8 pt 56.4 㫧 21.7 d**, 0.932 㫧0.142 d** 1.065 㫧 0.182 d*
f**

c**,

2

0.110

0.055

2.867

3

6.074

2.025 105.514

6

0.118

0.020

1.028

2

0.006

0.003

0.066

3

13.231

4.410

99.109

6

1.792

0.299

6.713 㩷12 pt 73.6 㫧 19.7 e**, 0.932 㫧0.104 e** 1.112 㫧 0.192 e**f****† Values in the same column with the same letters are
significantly different (**; p<0.01)† For example, 4 pt and 6 pt in the Participants'
evaluation column are given the letter 'a'. This meansthat the subjective evaluation of 6 pt character size
is significantly better than that of 4 pt.
**of the devices. Therefore, we next compared thecharacter sizes for each age group using a one–way
ANOVA. Table 6 and Figure 6 show a comparison

Table 5 provides a multiple comparison for theof the VAS by font sizes for each age group. For all

VAS, reading time index, and correct answer rate

age groups, the VAS scores for each font size wasindex. The VAS scores for the 4 pt font size (app 1.5

significantly lower as character point became smaller.

mm) were significantly lower than those of more than
6 pt size (2 mm). In fact, the scores were significantly
different between each of the font sizes. The reading
time index was significantly longer for the smaller
font sizes. The correct answer rate index was alsosignificantly lower per smaller font size.
The results from two-way ANOVA establishedthat the font sizes had an effect on the readability

Figure 6. Subjects’ evaluations under four character sizes

Table 6. Subjects evaluations of four fonts
1_Young
Mean㫧S.D

2_Middle
Mean㫧S.Da**,

4 pt 15.7 㫧 13.3

b**,
c**

a**,

12.7 㫧 12.2

a**,

6 pt 42.3 㫧 16.9

d**,
e**

12 pt 77.3 㫧 16.9

d**,
f**
c**,
f**

b**,
c**

35.0 㫧 16.9

d**,
e**

73.4 㫧 18.3

d**,
f**
c**,
f**

b**,
c**

a**,

7.7 㫧 8.6

a**,39.2 㫧 20.2

b**,57.4 㫧 19.5

4_Elderly
Mean㫧S.D

a**,

11.7 㫧 12.7

a**,

b**,

8 pt 64.2 㫧 17.2

3_Senior
Mean㫧S.Dd**,e**

76.8 㫧 18.3

d**,
f**
c**,
f**

† Values in the same column with the same letters are
significantly different (**; p<0.01)† For example, 4 pt and 6 pt in the Subjects' evaluation
column are given the letter ‘a’. This means that the
subjective evaluation of 6 pt character size issignificantly better than that of 4 pt

－ 83 －c**a**,24.7 㫧 21.3

b**,60.6 㫧 19.4

b**,

d**,
e**
b**,

37.0 㫧 22.3
63.2 㫧 23.3

d**,
f**
c**,
f**

社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

Table 7 and Figure 7 show a comparison of theTable 8 and Figure 8 show a comparison of thereading time index by font size for each age group.

correct answer rate index per font size for each

The reading time index for the younger and middle

age group. The correct answer rate index of allaged groups was significantly longer for the 4 pt. The

age groups for the 4 pt size was significantly lower

reading time index for the senior middle aged groupthan those of more than 6 pt. The correct answer

was significantly longer between the 6 pt and 8 pt

rate index of the middle aged group for 6 pt was

sizes. The reading time index of the elderly group

significantly lower than that of 12 pt size. The

was significantly longer at each font size between

differences in the proportion of slopes in the line

the 4 and 8 pt sizes. The elderly readers showed nograph (fig 8) for the young and middle aged groups

significant difference between the 4 pt and 6 pt sizes

were smaller than those for the senior middle aged

compared to the other age groups.

and elderly groups. The correct answer rate index

Table 7. Reading time index under four character sizes 㩷
1_Young
Mean㫧S.D

2_Middle
Mean㫧S.Da**,

3_Senior
Mean㫧S.Da*,4_Elderly
Mean㫧S.D

a**,

a**,

4 pt 1.132 ± 0.152

b**, 1.104± 0.109 b**, 1.161 ± 0.149 b**, 1.112 ± 0.189 b**

6 pt 0.996 ± 0.109

a** 0.991± 0.292 a* 1.011 ± 0.146 d**, 1.077 ± 0.179 d**

8 pt 0.936 ± 0.084

b** 0.952± 0.095 b** 0.919 ± 0.080 d** 0.932 ± 0.142 c**

12 pt0.936 ± 0.112

c**

c**

c**

c**

a**,

c**,

e**

b**,

a**,

c**,

b**,

0.952 ± 0.103 c** 0.920 ± 0.081 e** 0.932 ± 0.104 d**† Values in the same column with the same letters are
significantly different (**; p<0.01, *; p<0.05) using
ANOVA & the Scheffé multiple comparison procedure.

Figure 7. Reading time index under four character sizes 㩷

Table 8. Correct answer rate index under four character sizes㩷
1_Young
Mean㫧S.D

2_Middle
Mean㫧S.D

3_Senior
Mean㫧S.D

4_Elderly
Mean㫧S.D

a*,

a*,

a**,

a**,

c**

c**

c**

c**

4 pt 0.939 ± 0.200 b** 0.896 ± 0.210 b**, 0.732 ± 0.299 b**, 0.486 ± 0.334 b**,a*,

6 pt 0.997 ± 0.125 a* 1.006 ± 0.150 d* 1.033 ± 0.128 a** 0.988 ± 0.262 a**
8 pt 1.021 ± 0.129 b** 1.013 ± 0.161 b** 1.091 ± 0.16b**1.132 ± 0.26

c**,

b**

12 pt 1.042 ± 0.113 c** 1.085 ± 0.138 d* 1.124 ± 0.145 c** 1.213 ± 0.318 c**† Values in the same column with the same letters are
significantly different (**; p<0.01, *; p<0.05) using
ANOVA & the Scheffé multiple comparison procedure.

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社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

Table 10 and Figure 10 show the correct answer
rate index for the middle aged group. For the KV, the4 pt size was significantly lower than those of morethan 8 pt. No significant difference was observed
among character sizes with the iPad, while the 4 pt
size was significantly lower than those of more than
6 pt.
Table 10.
Correct
answerrate index
in themiddleTable
10.
Correct
answerrate
index
in agedthe group
middle aged group

1_KV
Figure8. Correct
answeranswer
rate index
underfour undercharactersizes
Figure8. Correct
rate
index
four
character 㩷sizes (Mean㫧S.D.)

for the 4 pt decreased greatly in the older groups.

2_iPad3_Paper(Mean㫧S.D.)(Mean㫧S.D.)
a**,

a*,

Because the correct answer rate index had the mostdifference for each age group among all the indices,

4 pt 0.888 ± 0.199 b** 0.960 ± 0.167

0.839 ± 0.239 b**,0.970 ± 0.120

1.023 ± 0.150 a**

8 pt 1.060 ± 0.095 a* 0.922 ± 0.172

1.058 ± 0.165 b**

6 pt 1.026 ± 0.168c**

we analyzed the data by types of devices for eachage group by using a one-way ANOVA.
Table 9 and Figure 9 show the correct answer
rate index for the younger group of readers. The KV

12 pt 1.092

had significantly lower ratings between the 6 and

0.136 b** 1.029

0.148

1.134

0.105 c**† Values in the same column with the same letters are
significantly different (**; p<0.01, *; p<0.05) using
ANOVA & the Scheffé multiple comparison procedure.

8 font sizes. No significant difference was observed
among the font sizes for the iPad, while 4 pt size wassignificantly lower than the 6 pt for the Paper text.
Table 9. Correct answer rate index in the younger
1_KV㩷(Mean㫧S.D.)

2_iPad3_Paper(Mean㫧S.D.)(Mean㫧S.D.)

a**,

a**,

4 pt 0.893 ± 0.191 b* 1.070 ± 0.126

0.854 ± 0.204 b**,

6 pt 0.931 ± 0.129 c* 1.011 ± 0.112

1.051 ± 0.103 a**

a**,

c**

8 pt 1.065 ± 0.085 c* 0.965 ± 0.150

1.034 ± 0.124 b**

12 pt 1.018 ± 0.104 b* 1.030 ± 0.124

1.079 ± 0.099 c**

Figure10. Correct
answer rateindex inthe index
middle aged
group
Figure10. Correct
answerrate
in themiddle aged group

Values in the same column with the same letters are
significantly di†fferent (**; p<0.01, *; p<0.05) using
ANOVA & the Scheffé multiple comparison procedure.

Table 11 and Figure 11 show the correct answer
rate index for the senior middle aged group. For all
devices, the 4 pt size was significantly lower thanthose of more than 6 pt size. For this age group,
there was no significant difference in the correct
answer rating between the 6 pt and 12 pt sizes.
Table 12 and Figure 12 show the correct answer
rate index for the elderly group. For the KV and iPad,the answers were significantly lower at the 4 pt size
compared to more than 6 pt size. For paper, the 4 pt
size was significantly lower than the 6 pt size which

Figure 9. Correct answer rate index in the younger group 㩷

in turn was significantly lower than that of the12 pt－ 85 －

社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

4 Discussion
The primary aim of this experiment was to identify
how well different groups evaluated the readabilityof different font sizes for two types of electronic
devices. This experiment was conducted under 1,000lx
of illuminance to eliminate the effect of ambient
illuminance on the readability of the e-paper. In ourprevious studies, we found no significant differenceson the readability of an e-paper, LCD, and paper atthe 1,000 lx level10,11).

Figure11.11.
Correct
answerrate index
the senior
aged
FigureCorrect
answerrate inindex
in themiddle
senior
middle aged group 㩷

We used the Courier font type because it is amonospaced font recommended for such studies
Table 12.Correct answer rate index in the elderly group

㩷

1_KV

2_iPad3_Paper(Mean㫧S.D.)(Mean㫧S.D.)(Mean㫧S.D.)

a**,

a*,

㩷

by the ISO7). In addition, in order to conform to ourprevious studies, we measured the character heights
in millimeters to ensure compatibility. Studies havereported that Courier is a viable font for the elderlya**,4 pt 0.434 ± 0.286 b**, 0.554 ± 0.356 b**, 0.452 ± 0.333 b**,
c**

c**

suffering with vision problems including macular

6 pt 1.018 ± 0.289 a** 0.957 ± 0.233 a*

0.986 ± 0.255 d*a**,degeneration12).

c**

8 pt 1.023

0.269 b** 1.116

0.253 b** 1.254

12 pt 1.194

0.251 c** 1.134

0.389

c**

1.310

This experiment sought to identify what would
be the lower limit font height at which participants

0.197 b**

could maintain their reading performance. We testedc**,0.270 d*for reading speed and correct answer rate, while also

† Values in the same column with the same letters are
significantly different (**; p<0.01, *; p<0.05) using
ANOVA & the Scheffé multiple comparison procedure.

looking at how font sizes effect readability for older
individuals. We set the text font sizes at four levels; 4pt (character height: 1.4 mm), 6 p (character height: 2mm), 8 pt (character height: 2.75 mm), 12 pt (characterheight: 3.25 mm).
In this study the VAS scores for 8 pt font size
showed an average evaluation scores above 50. We
found that the participants felt that the characterheight of more than 2.75 mm (8pt) was sufficiently
readable. The reason may have been due to lighting
differences or the differences in resolutions. The
screen resolutions for both the KV and iPad were
well above 150 ppi (Table 3). Previous studies have

Figure 12. Correct answer rate index in the elderly group

Figure 12. Correct answer rate index in the elderly groupshown that participants’ evaluations of readability

size. The differences in the proportion of the slopes in
the line graph (fig 12) for font sizes in the young andmiddle aged groups were smaller than those of thesenior middle aged and elderly groups. For the older
group, the correct answer rate index for the 4 pt fontdecreased significantly compared to the other groups.
This was especially true for the rating of the readingfrom the KV (p<0.01).

were higher when resolutions of the device were
between 150 ppi to 400 ppi13).
In this study, the 4 pt font size for all the devices
showed significantly low values for participant
evaluations, reading time index, and correct answer
rate index. Lee et al. also reported that the legibilityof the 1.4 mm character height size was lower
than that of 2.2 mm 14). The results in this study－ 86 －

社会医学研究．第 34 巻 1 号．Bulletin of Social Medicine, Vol.34（1）2017

also suggests that the minimum font size at which

and aging on the readability of e-books. The findings

participants (64 years old or younger) can maintainin this experiment can be summarized based on thetheir reading performance for an e-paper is at about

readability of the font size and the devices.

5.1 Font sizes

2 mm (6 pt).
Furthermore, the VAS scores were plotted as an(1) The participants felt that the screen font size

increasing straight-line from the 4 pt to 8 pt font sizes(character height) of 2.75 mm (8 pt) was readable.

(fig 6). There was a gentle curve that represented a

For all ages, we recommend a font size of more thansignificant increase in the scores between the 8 pt

2.75 mm as a default size displayed on the screens ofand 12 pt font sizes. In this study, we found that theelectronic devices.

character height size of 2.75mm (8 pt font size) was(2) The minimum font size level at which thosethe lower limit to which reading speed decreased

readers under 65 years of age could maintain theirsignificantly. The correct answer rate index showed

performance (there was no decrease in reading speed

that a significant increase between 4 pt and 6 pt

and correct answer rate) was the character height of(p<0.01), and some increase between 6 pt and 8 pt

2 mm (6 pt). The visual performance of those over 65(p<0.05).

years of age decreased in below 2.75 mm.

There was no significant difference between the(3) All groups saw a decrease in reading speed

8 pt and 12 pt font sizes. Thus, we can suggest that

below the 2.75 mm (8 pt) font size. As a result wethe lowest limit that participants can read words

recommend this size as the minimum limit.

accurately is the character height size of 2.75mm

5.2 Devices(8 pt font size) for e-paper devices. The LCD with a(1) The readability of the two electronic devices

backlit assisted those under the middle aged group

we used in this study performed equally to paperwith reading proficiency with font sizes less than 2

text. However, these devices are more advantageous

mm (6 pt)., but was not helpful for those in the older

because they allow the reader the opportunity to thegroup.

change font sizes. This is particularly helpful to theTable 2 showed that the elderly suffer from higher

elderly.

cataract cloudiness compared to younger people. One(2) The front lighting system on e-papers worksof our previous studies reported that high cataract

well for improving readability. Furthermore, reading

cloudiness decreased the ability to read from tablet

is improved when the screen resolution is greater

15)

devices . Cataract cloudiness plays a role similar tothan 150 ppi.

frosted glass which can diminishing effect on how lightenters the eye. Thus, while the minimum font size for

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