j.1475-1313.2011.00886.x

Prevalence of myopia among Hong Kong Chineseschoolchildren: changes over two decadesCarly Siu-Yin Lam1,2, Chin-Hang Lam1,2, Sam Chi-Kwan Cheng1 and Lily Yee-Lai Chan1,2

1Centre for Myopia Research, School of Optometry, The Hong Kong Polytechnic University, Hong Kong, and 2Sports Vision Unit, The Hong Kong

Jockey Club Sports Medicine and Health Sciences Centre, The Hong Kong Polytechnic University, Hong Kong

Citation information: Lam CS-Y, Lam C-H, Cheng SC-K & Chan LY-L. Prevalence of myopia among Hong Kong Chinese schoolchildren: changes

over two decades. Ophthalmic Physiol Opt 2012, 32, 17–24. doi: 10.1111/j.1475-1313.2011.00886.x

Keywords: Chinese, myopia, prevalence,

schoolchildren

Correspondence: Carly S-Y Lam

E-mail address: [email protected]

Received: 26 March 2011; Accepted: 11

November 2011

Abstract

Purpose: Studies have documented an increasing prevalence of myopia among

urbanized Asian countries over recent decades. In the early 1990s, the reported

prevalence rate was 25% and 64% for 6 and 12 year old children respectively.

This cross-sectional study aims to determine the current prevalence of myopia

amongst Hong Kong Chinese schoolchildren and whether there has been any

increase over the last two decades.

Methods: Data from 2651 children aged 6–12 (mean age: 8.92 ± 1.77, 53%

boys) who participated in vision screening during 2005–2010 were analyzed.

Visual parameters including visual acuity (in logMAR) and binocular status

under the participants’ habitual correction were assessed. Refractive errors were

examined using non-cycloplegic auto-refraction and axial lengths were mea-

sured by partial coherence interferometry.

Results: The mean spherical equivalent refraction for this population was

)1.02 ± 1.70D, ranging from +4.75 to )10.00D. Prevalence of myopia (more

than )0.50D) was 18.3% for the 6-year-old group and 61.5% for the 12-year-

old group. Average myopia magnitude was )0.06 ± 1.03D at age 6 and

)1.67 ± 1.99D at age 12. Prevalence of high myopia of more than )6.00D was

1.8%, with an increase from 0.7% at the age of 6 to 3.8% at the age of 12.

Conclusions: The prevalence of myopia among the Chinese schoolchildren pop-

ulation in Hong Kong as observed in this cross-sectional study are similar to

our previously reported findings from almost two decades ago. There is no

evidence that prevalence of myopia is increasing with time over the last two

decades. However, the prevalence and degree of myopia in Chinese children is

high as compared with other ethnic groups such as those reported among

Caucasians.

Introduction

Around 70–80% of young adults living in East Asian

countries such as Taiwan, Japan, Hong Kong and Singa-

pore have myopia.1–4 Studies published within the last

few decades have shown an increasing rate of myopia that

may even be described as an ‘epidemic’.1–3,5 In Taiwan,

myopia prevalence has increased from 5.8% in 1983 to

21% in the year 2000 among children aged 7 and from

36.7% in 1983 to 61% in the year 2000 for children aged

12.1 In Japan, 37.6% of Japanese children aged 12 were

myopic in the late 1970s and the rate rose to 43.5% by

the early 1990s.3 In Singapore, among the children and

young male adult population, the proportion of individu-

als with impaired unaided vision presumably due to myo-

pia increased rapidly, from 2.0% in 1954 to 49.2% in

19935 and from 26% in the late 1970s to 83% in the late

1990s respectively.2 These reports present a remarkable

trend that illustrates both an increase in prevalence as

well as severity of myopia documented within the last ten

Ophthalmic & Physiological Optics ISSN 0275-5408

Ophthalmic & Physiological Optics 32 (2012) 17–24 ª 2011 The College of Optometrists 17

to thirty years despite differences in the definition of

myopia and methodology.6

The occurrence of myopia has long been associated

with genetic and environmental influences. It has been

suggested that possible genetic susceptibility among spe-

cific ethnic groups such as the Chinese population2,5 and

environmental factors including increased near work

demands, implementation of education and urbaniza-

tion1–3 contribute to this rising trend. Among this popu-

lation, the onset of myopia occurs at a young age,

approximately as children enter mainstream educa-

tion.1,4,7–10 The time of myopia onset also plays an

important predictor to the progression rate of myopia.

That is, the younger the age of onset, the more severe the

myopic refractive error.11,12 Previous studies have identi-

fied variables in education and schooling as risk factors

for myopia development in children. In addition, numer-

ous reports have indicated that a school curriculum con-

sisting of more near work demands is associated with a

higher rate of myopia or impaired distance vision13,14 and

a faster rate of myopia progression.15 Furthermore, an

academic curriculum for early-school children plays a sig-

nificant role in myopia development compared to disci-

pline-based activities.16 Thus, early schooling and a

competitive education system could have detrimental

effects on the overall prevalence of myopia among

Chinese schoolchildren.

In Hong Kong, a 9-year compulsory formal education

has been established since the 1970s with all children aged

5–6 years being required to commence 6 years of primary

and 3 years of junior secondary school education. By the

early 1990s, longer hours of schoolwork were required as

the public school system implemented a full-day program

to replace a previously established half-day program.

Additionally, it was around this period where the popu-

larity of pre-school education (for children as young as

2 years) grew, indicating that most children would have

attended kindergarten for 3 years before entering primary

school. Alongside the 1990s information technology boom

in multi-media, computer and the internet, many schools

have since implemented online self-studies as an integral

part of their curriculum. However, controversial findings

still exist on whether computer-use is a risk factor to

myopia development in children.17,18

While competitive demands in the number of hours

spent on extra-curricular activities and supplementary

tutorial classes continue to rise, no significant changes in

Hong Kong’s education have been noted since the 1990s

other than a transition from a half-day to full-day primary

schooling. This has led us to the question whether an

increase in near work as a result of more hours spent on

tutorial classes is significantly associated with changes in

the prevalence rate of myopia. Our previous cohort stud-

ies in 1991 and 1993 have already reported a 25% and

21% myopia prevalence rate respectively among 6 year-old

schoolchildren. This rate increased to 64% and 75% for

those aged 12.4,19 Here, we aim to determine and compare

the prevalence of myopia over the last two decades by pre-

senting cross-sectional results and investigating whether

there are any significant changes within this period.

Methods

Subjects

The current study was part of a multi-disciplinary health-

screening program that encompassed physical, dietary,

visual and paediatric health assessment for primary school-

children during the period of late 2005 to early 2010. Six

local primary schools (n = 4404 children) from different

locations in Hong Kong with a total of 2883 children aged

5–15 participated (participation rate: 65%) in this cross-

sectional study. All the schools were full-day public schools

representing the typical Hong Kong formal education.

Separate information letters covering the specific scope

of this investigation were given, via the schools to parents

and children of all grades (1–6). This study was approved

by the Human Subjects Ethics Sub-committee of the

Hong Kong Polytechnic University and adhered to the

tenets of the Declaration of Helsinki. Written consents

were obtained from parents prior to data collection and

verbal consents were also obtained from the children.

Definition of refractive errors

For comparison purposes, refractive errors in this study

were defined using the same criteria as our previous

work. Spherical equivalent refraction (SER) was calculated

as the sum of spherical refractive power and one-half of

the cylindrical (astigmatic) refractive power. Myopia,

hyperopia and emmetropia were defined respectively as

SER of more than 0.50D of myopia, more than 0.50D of

hyperopia and between +0.50D and )0.50D inclusive.

Examination details

All tests described below were conducted by trained inves-

tigators, optometrists and optometric interns.

Visual acuity and binocular vision assessment.

Presenting distance visual acuity (VA) was measured

monocularly for both eyes under an illumination of at

least 480 lux using the Bailey-Lovie logMAR chart con-

sisting of English alphabet letters placed at 6 m away.

Binocular status of children at both distant and near was

screened by the cover testing method over their habitual

correction.

Changes in myopia prevalence over two decades CS-Y Lam et al.

18 Ophthalmic & Physiological Optics 32 (2012) 17–24 ª 2011 The College of Optometrists

Non-cycloplegic refractive error.

Non-cycloplegic refractive errors were measured with an

open-field auto-refractor (Shin-Nippon NVision-K 5001,

http://www.shin-nippon.jp). Each subject was instructed

to view a visible target at a distance of 6 m from their

direct frontward line of sight throughout the measure-

ments. At least three representative values from the auto-

refractor were generated as an averaged measurement for

data analysis. Data deemed unreliable were rejected and

re-measured. Cycloplegic refraction was not performed to

minimize interruption in the regular school schedule dur-

ing these multidisciplinary health screenings. Data from

the 1990s study were also reported as results from non-

cycloplegic subjective refraction.

Ocular biometry (axial length and mean corneal curvature).

Ocular biometry values (including keratometry readings)

were measured using the IOLMaster Optical Biometer

(http://www.meditec.zeiss.com). The mean axial length

was obtained from at least three measurements. Any

within-measurement deviations of more than 0.10 mm

were discarded. Keratometric readings of the two princi-

pal meridians obtained from each subject were used to

yield the mean corneal radii of curvature (Kmean) and

corneal toricity (Kdiff).

Data analysis.

Both eyes of each subject were assessed. Only data from

the right eye were presented since data between the left

and right eye were highly correlated (Pearson r = 0.93 for

SER, p < 0.001; Pearson r = 0.97 for axial length, p <

0.001; Pearson r = 0.97 for mean corneal curvature p <

0.001). Any missing values due to uncooperative subject

participation were regarded as incomplete data sets and

they were not included in analysis (n = 30). Children

with known systemic or ophthalmic conditions (n = 13),

strabismus or decompensated phorias (n = 104) and

those of non-Chinese ethnicity (n = 11) were excluded

from data analysis. Participants aged 5 and ‡13 (n = 74)

were further excluded because of low statistical power to

be considered as representative population groups.

For descriptive statistics, continuous variables including

age, SER, axial length and Kmean were expressed as

mean ± 1 standard deviation (S.D.) while categorical vari-

ables including gender, prevalence of myopia, hyperopia

and emmetropia were expressed as percentages (95% con-

fidence interval, CI). Comparison between distributions

of variables was tested with the Kolmogorov-Smirnov test.

Means of independent groups were compared with

unpaired tests (Student t-test and Mann-Whitney test for

parametric and non-parametric data respectively) and

categorical data between groups were tested with v2.

One-way anova was used in comparing continuous vari-

ables among age groups. Pearson correlations were used

to describe the relationship between age and ocular

biometric data. All the analyses were performed with

commercially available software SPSS v.16 (http://

www-01.ibm.com/software/analytics/spss).

Results

The data from a total of 2651 children aged 6–12 (mean

age = 8.92 ± 1.77 years) were analyzed. The sample com-

posed of 53.2% (95% CI 51.3–55.1%) boys and 46.8%

(95% CI 44.9–48.7%) girls and there was no gender dif-

ference in distribution (Kolmogorov-Smirnov test, Z =

0.93, p = 0.35) but boys (mean age = 9.00 ± 1.76 years)

were slightly older than girls (mean age = 8.84 ± 1.78

years) (Mann-Whitney test, U = 831000, p = 0.02). Age

and gender distribution are illustrated in Table 1.

Table 1. Mean ± 1 S.D. refractive errors and ocular components in primary schoolchildren

Age Sphere (D) Cylinder (D)

Axial length (mm) Kmean (D)

Boys Girls Boys Girls

6 0.24 ± 1.00 )0.61 ± 0.54 23.06 ± 0.69a 22.56 ± 0.93 43.02 ± 1.43a 43.69 ± 1.33

7 0.04 ± 1.08 )0.66 ± 0.55 23.30 ± 0.76a 22.81 ± 0.79 43.15 ± 1.31a 43.80 ± 1.39

8 )0.61 ± 1.41 )0.61 ± 0.48 23.67 ± 0.90a 23.10 ± 0.84 43.19 ± 1.38a 43.85 ± 1.26

9 )0.74 ± 1.54 )0.61 ± 0.56 23.95 ± 0.96a 23.25 ± 0.86 43.08 ± 1.35a 43.93 ± 1.31

10 )1.10 ± 1.77 )0.66 ± 0.59 24.13 ± 1.04a 23.64 ± 1.00 43.20 ± 1.37a 43.78 ± 1.29

11 )1.35 ± 1.89 )0.65 ± 0.56 24.36 ± 1.05a 23.82 ± 1.05 43.06 ± 1.28a 43.80 ± 1.39

12 )1.34 ± 1.89 )0.66 ± 0.60 24.41 ± 1.11a 23.81 ± 1.07 42.99 ± 1.34a 43.94 ± 1.42

6–12 )0.70 ± 1.64 )0.63 ± 0.55 23.86 ± 1.04b 23.26 ± 1.02 43.12 ± 1.35a 43.82 ± 1.33

rc )0.33* )0.02 0.41* 0.42* )0.01 0.03

aSignificant gender difference (unpaired t test, p < 0.001).bSignificant gender difference (Mann–Whitney test, p < 0.001).cPearson correlation coefficient r between age and each variable (sphere, cylinder, axial length and Kmean); *p < 0.001.

CS-Y Lam et al. Changes in myopia prevalence over two decades


Prevalence of refractive errors

The overall prevalence of myopia, emmetropia and hyper-

opia were 47.5% (95% CI 45.6–49.4%), 44.4% (95% CI

42.6–46.3%) and 8.1% (95% CI 7.1–9.2%) respectively.

There were no significant gender differences observed in

myopia prevalence between boys (48.9%, 95% CI 46.3–

51.6%) and girls (45.8%, 95% CI 43.0–48.5%) (v2 = 1.39,

p = 0.24). Myopia prevalence increased gradually from

18.3% (95% CI 13.8–22.7%) at age 6 to 61.5% (95% CI

54.5–68.6%) at age 12. For the same age range a decrease

in prevalence of hyperopia and emmetropia were

observed with age from 15.9% (95% CI 11.7–20.1%) to

4.9% (95% CI 1.8–8.1%) and from 65.9% (95% CI 60.4–

71.3%) to 33.5% (95% CI 26.7–40.4%) respectively

(v2 = 272.2, p < 0.001) (Figure 1). For high myopia of

more than )6.00D, the average prevalence was 1.8% and

increased from 0.7% at age 6 to 3.8% at age 12 (Figure 1).

Figure 2 illustrates the SER distribution of refractive

errors that is skewed towards the myopic side and less

leptokurtic when comparing children aged 12 with those

aged 6. There was no difference in the distribution of

SER between genders (Kolmogorov-Smirnov test, Z =

1.07, p = 0.20).

Refractive errors and ocular components

The mean SER was )1.02 ± 1.70D, ranging from +4.75 to

)10.00D. Table 1 illustrates a gradual increase in myopia

from ages 6–12 where spherical error decreased with age

(anova, F1,2649 = 314.2, p < 0.001; Pearson r = )0.33,

t = )17.7, p < 0.001) while cylindrical error remained rel-

atively stable with age (anova, F1,2649 = 0.98, p = 0.32;

Pearson r = )0.02, t = )0.99, p = 0.32). Correlation

between mean SER and age was significant (Pearson

r = )0.32, p < 0.001). The mean SER of schoolchildren

aged 6 was )0.06 ± 1.03D and )1.67 ± 1.99D at the age

of 12 years; the SER increased in the myopic direction

and became more negative.

A comparison of axial length and Kmean with age

showed that axial length increased with age (anova,

F1,2649 = 539.4, p < 0.001; Pearson r = 0.41, t = 23.2,

p < 0.001) while Kmean remained relatively stable with age

(anova, F1,2649 = 0.09, p = 0.76; Pearson r = )0.01,

t = )0.30, p = 0.76) (Table 1). A significant gender differ-

ence was present. A boy’s axial length (23.86 ± 1.04 mm)

was significantly longer than that of a girl’s (23.26 ±

1.02 mm) (Mann-Whitney test, U = 586900, p < 0.001)

and the Kmean of girls (43.82 ± 1.33D) was significantly

steeper than boys’ (43.12 ± 1.35D) (unpaired t-test, t2649

= )13.6, p < 0.001). This pattern was consistent for all

ages (Table 1).

Discussion

Comparison with other studies

The prevalence and refractive error trend reported in this

study, like most findings in other cross-sectional studies

have shown an increase in the prevalence of myopia with

age and the severity of SER becoming more myopic with

age.3,20–23 Among Chinese studies, in particular, both

changes in myopia prevalence and severity are found to

be more vigorous and severe.1,4,7–10,19,24 For example,

Figure 3 illustrates prevalence findings in two studies

reported in the early 1990s: a non-cycloplegic subjective

refraction conducted on 383 children aged 6–17 4 and a

non-cycloplegic close-field auto-refraction conducted on

1247 children of the same age range.19 The prevalence of

Figure 1. Proportion of refractive errors across age groups: Hyperopia (SER > +0.50D), emmetropia (SER = ±0.50D), myopia ()0.50D < SER

£ )6.00D) and high myopia (SER < )6.00D). Key. SER: Spherical equivalent refraction.



myopia in children aged 6 and 12 are 25% and 64%

respectively in the former report 4 whilst they are 20.6%

and 74.8% in the latter study.19 For these Hong Kong fig-

ures detailed since 1991, the reported differences ranged

from 5 to 10%. Furthermore, a similarity in the mean SER

and the prevalence of myopia as well as high myopia is

observed (Table 2). Another local study using cycloplegic

auto-refraction results from 7560 children in the late 1990s

reported that myopia prevalence increased from 17% at

ages <7 to 53.1% at ages ‡11.8 Presumably, because cyclo-

plegia and a different definition of myopia were used, the

rate and severity are generally lower. Hence, these values

should not be considered as a true difference. A more

recent study on Canadian-Chinese children (from a second

generation of Hong Kong immigrants) living in Ontario

reported a manifest myopia incidence of 22.4% and 64.1%

for children aged 6 and 12 respectively.7 The mean SER for

this clinic population rises from )0.02 ± 1.02D at age 6 to

)1.97 ± 2.04D at age 12. This is very close to the percent-

age values obtained in our current study which may sug-

gest that furthermore to myopia prevalence, the severity

and myopia trend in children between these populations

may be similar.

High myopia trend

The prevalence rates of high myopia in this study are

0.7%, 0.0%, 1.4%, 1.6%, 1.7%, 3.8% and 3.8% from ages

6 through to 12. In the 1991 study, similar to our current

findings, the prevalence of high myopia is essentially none

Figure 2. Distribution of SER of age 6 and 12; group ‘‘0.00D’’ denoted SER = ±0.50D inclusively; group ‘‘)1.00D’’ for )0.50D > SER ‡ )1.50D,

‘‘)2.00D’’ for )1.50 > SER ‡ )2.50D, and so on; similarly for hyperopic groups. Key. SER: Spherical equivalent refraction.

Figure 3. Prevalence of myopia of different ages reported in 1991,

1993, 2004, and the current study; the four data points at age 6.5,

8.5, 10.5 and 12.5 of 1991 plot denoted age 6–7, 8–9, 10–11, 12–

13 respectively; data points at 6 and 11 of 2004 plot denoted age 5–

6 and 11–15 respectively.

Table 2. Myopia status in the current study and study in 1991

1991 Current

Age 6 Prevalence of

myopia (%)

25% 18.3%

Prevalence of

high myopia (%)

0% 0.7%

Mean

SER ± S.D. (D)

)0.03 ± 1.73D )0.06 ± 1.03D

Age 12 Prevalence of

myopia (%)

64% 61.5%

Prevalence of

high myopia (%)

4% 3.8%

Mean

SER ± S.D. (D)

)1.45 ± 1.96D )1.67 ± 1.99D



for age 6 and at 4% for age 12. Additionally, Lin et al.

(2004) found an increasing trend of high myopia with

time: at age 12, reported values are 0.2%, 0.7%, 0.5%, 2%

and 3.4% as reported in 1983, 1986, 1990, 1995 and 2000

respectively. Their figures reported in the year 2000, clo-

sely match the findings reported here. At this time, the

rate of high myopia among young children is low (1.4%

for ages 7–9).25 Note however, a recent Singaporean

young adult study reported an increase in high myopia

prevalence rate within the recent 12 years, rising from

13.1% to 14.7%.26

Strengths and limitations

To the best of our knowledge, this is the first large scale

vision screening program for Hong Kong schoolchildren

that uses an open-field auto-refractor, which allows

refraction to be performed under a natural viewing con-

ditions. Direct comparisons between studies are however,

difficult due to factors such as cohort effects, the lack of a

universal definition of myopia and differences in sam-

pling methodology, refraction technique and whether

refraction was performed under cycloplegic or non-cyclo-

plegic conditions. To match our previous studies, myopia

is defined as an SER of more than )0.50D of myopia and

refraction is performed without cycloplegia accordingly.

In order to minimize unavoidable cohort effects and dif-

ferences in sampling methods, all schoolchildren from

each participating school have been invited and self-

selected in urbanized areas from public school programs

that represent the typical Hong Kong education system

similar to our studies in the 1990s. The study also pro-

vides data from a large sample size. The open-field auto-

refractor used in this study minimizes unnecessary

accommodative fluctuations, which is evident with a

closed-field auto-refractor. Additionally, the sensitivity

and specificity it yields in the diagnosis of myopia with-

out cycloplegia have been demonstrated in both the adult

and children populations.27–30 The paired difference

between with and without cycloplegia is 0.18 ± 0.37D in

young children with a myopic SER of more than 0.00D

(non-cycloplegic conditions yielded a higher degree of

myopia) and such differences are greater in emmetropic

and hyperopic children.29 A similar study further demon-

strated that non-cycloplegic autorefractor results closely

approximate a non-cycloplegic subjective refraction.30

Moreover, their results show that autorefraction results

were comparable to subjective refraction in terms of

objectivity, repeatability and accuracy. Thus, the results

generated from the open-field auto-refractor employed in

our study are directly compared with previous studies

that use a subjective refraction with or without cyclople-

gia, allowing for a minimal over-estimation error.

A plateau effect on myopia prevalence?

Despite the changes in Hong Kong’s education system

and children’s learning behaviour, we have not observed

any increases in the trend for both the prevalence and

severity in myopia when comparing the past and current

cohorts within a span of two decades. The prevalence rate

reported in the 1990s is purportedly already among one

of the highest when compared with studies from other

countries. At the time those previous reports were pub-

lished, myopia development among this population age

group may have had already reached its highest capacity.

One may even postulate that this was in response to the

introduction of an intensive and early commencement of

schooling where children were raised in a competitive

lifestyle environment, alongside urbanization during that

period. Further risk factors have not yet increased the

overall prevalence and severity of myopia since those

times and a stabilization of myopia prevalence within this

age group is observed in this study. Considering that the

biological aspect of an eye, its ocular growth, and refrac-

tive development are determined by both visually guided

stimulation and pre-determined by genetics, chick studies

have also shown a similar plateau effect in refraction that

is dependent on the amount of induced or myogenic

stimulation.31

Likewise, in recent years, a stabilized trend in the prev-

alence of myopia among schoolchildren has also been

observed in Taiwan despite the fact that there are reports

of myopia increasing in the early 1990s.1,32 Shih reported

that the prevalence of myopia as well as high myopia has

remained unchanged in 2006.32 It is possible that the

increase in myopia prevalence and severity in those earlier

studies reflected the different stages of myopia develop-

ment in their respective ethnic and environmental condi-

tions. Further work to cover more cohorts within

different time spans shall reveal whether a saturation

effect can be reached, especially in places that are under-

going urbanization alongside improvements in a more

academic-based education system. Of further clinical

interest is the change in visual media presentations and

the visual constraints these will demand on novel users.

Children are spending more time using digital screens

instead of reading from printed books due the introduc-

tion of electronic education in the form of notebook

computers, e-books as well as electronic games as their

standard visual platform. The habits children derive from

using these devices may impose particular effects on their

visual system. The differences between the visual stimula-

tion of an electronic screen as compared to conventional

textbooks are not yet known. Further investigation into

this aspect is needed to identify its impact on myopia

prevalence in Hong Kong.



Conclusion

The prevalence of myopia among the Chinese schoolchil-

dren population in Hong Kong as observed in the current

study is similar to our previously reported findings from

almost two decades ago. There is no evidence that the

prevalence of myopia is increasing with time. However,

the rate and the mean spherical equivalent are still high

as compared with other ethnic groups particularly Cauca-

sians. It is postulated that myopia prevalence among

Hong Kong schoolchildren may have reached a ‘saturated’

level and that the plausible myopigenic environmental

influences may have already maximized their effect and

have by now, reached a stabilized state. Further longitudi-

nal observation is required to determine future trends in

the prevalence of myopia.

Acknowledgements

We would like to thank the teachers, students and parents

from Farm Road Government Primary School, Ma On

Shan Lutheran Primary School, The Little Flower’s Catho-

lic Primary School, Pentecostal Yu Leung Fat Primary

School, CCC Kei Chun Primary School and Tai Kok Tsui

Catholic Primary School for their participation in this

study. This study was made possible from equipment/

resources donated by The Hong Kong Jockey Club Chari-

ties Trust and Niche Areas Fund (J-BB7P) from The

Hong Kong Polytechnic University.

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