Prevalence of Nocturnal Enuresis and Associated Familial Factors in Primary School Children in Taiwan

0022-5347/02/1683-1142/0 THE JOURNAL OF UROLOGY® Copyright © 2002 by AMERICAN UROLOGICAL ASSOCIATION, INC.®

Vol. 168, 1142–1146, September 2002 Printed in U.S.A.

DOI: 10.1097/01.ju.0000025872.38494.43

PREVALENCE OF NOCTURNAL ENURESIS AND ASSOCIATED FAMILIAL FACTORS IN PRIMARY SCHOOL CHILDREN IN TAIWAN TSANG-WEE CHER, GHI-JEN LIN

AND

KUANG-HUNG HSU*

From the Division of Pediatric Nephrology, Department of Pediatrics, Chang Gung Children’s Hospital and Laboratory for Epidemiology, Department of Health Care Management, Chang Gung University, Taiwan, Republic of China

ABSTRACT

Purpose: We investigated the prevalence and associated factors of nocturnal enuresis in children in elementary schools in Taiwan. Materials and Methods: A cross-sectional study of nocturnal enuresis in Taiwanese school children was performed in 10 primary schools in Tao-Yuan County, Taiwan. Questionnaires on demographic data, familial and physical conditions were completed by 7,225 children assisted by their parents. Results: The overall prevalence of nocturnal enuresis in Taiwanese primary school children was 5.5%. Decreasing age, male gender, family size, birth rank, parental education level and parental raising style were possible familial risk factors for nocturnal enuresis in this study. Conclusions: The study indicates a prevalence of nocturnal enuresis in the Taiwanese population comparable to that in western populations, showing that nocturnal enuresis is an international problem that should be considered seriously. Findings of familial factors associated with nocturnal enuresis provide a clue for future studies of psychosocial factors in different cultural societies and their intervention. KEY WORDS: bladder, enuresis, questionnaires, parents, family

Nocturnal enuresis is a common medical condition in children in western societies. Definitive therapies, such as desmopressin or an enuretic alarm, must be implemented as soon as possible to avoid undesirable psychological consequences, such as low self esteem.1 Although the prevalence of nocturnal enuresis has been determined in various surveys done in North America2 and in European countries,3–5 rare reports have addressed the problem in Asian populations. Of 4 to 12-year-old Chinese children residing in Hong Kong only 3.5% were noted to have enuresis problems.6 The lower prevalence may somehow show an etiological differences in the east and west. It is important to note that the population of Hong Kong has already been westernized in terms of lifestyle and diet. Therefore, availability of the prevalence rate in a comparatively native population would enable us to understanding further the uniqueness of this childhood condition in Asia. On the other hand, Taiwan may represent a valuable population for this purpose. In this study a questionnaire that designed with local characteristics and language was administered to evaluate the prevalence of nocturnal enuresis in Taiwanese children. In addition to this primary objective, the questionnaire also recorded other factors useful for establishing a familial connection with this childhood disorder. Briefly, we evaluated the prevalence of nocturnal enuresis in Taiwanese children and possible familial factors associated with this childhood disorder. MATERIALS AND METHODS

This study was performed at 10 primary schools in TaoYuan County, a suburban region near Taipei City. A specific questionnaire prepared in the local language was distributed

to 8,997 students 6 to 12 years old in these schools. The parents of these students were requested to complete the first 2 sections of the questionnaire, which surveys the demographic, familial and physical conditions of their children. Furthermore, whether the children had enuresis was also documented as well as the frequency and family history of enuresis. In this questionnaire nocturnal enuresis was defined as unaware voiding of urine during sleep at night. Enuresis was defined as an episode of wetting occurring at least once monthly. Daytime conditions, such as incontinence, were differentiated by separate questions. Data were summarized according to the cross-sectional design. Statistical analyses were done by the chi-square test for comparing differences in categorical variables in enuresis cases and controls. The strength of association of different demographic and familial factors with enuresis was measured by the odds ratio with the Mantel-Haenszel chi-square test on univariate analyses. Multiple logistic regression analysis was applied to calculate multivariate adjusted odds ratios for variables of interest. The prevalence of enuresis and associating familial factors in this cohort of Taiwanese primary school students are presented in this report. RESULTS

Of the 8,997 questionnaires distributed 7,302 (81.2%) were collected and 7,225 (80.3%) that were completed entered the final analysis. More than half of the questionnaires were completed by the mother (61.4%), while response by the father accounted for a third of the cohort. Less than 3% of the questionnaires were completed by nonparental guardians. These subjects are ethnically Taiwanese and gender was equally distributed (49.5% females and 50.5% males). Mean age of the subjects was 8.71 years (95% confidence interval 5.21 to 12.22). Of all the analyzed children 399 (5.52%) had enuresis and 41 (10.3% of those with enuresis) also had daytime incontinence. An average of 1.71 wet nights weekly were due to enuresis. Stratification of the subjects into age groups revealed a higher prevalence in children younger

Accepted for publication April 19, 2002. Supported by Grants CMRP 599 and CMRP 1210 from Chang Gung Research Fund of Taiwan and Ferring Pharmaceuticals Ltd. * Requests for reprints: Laboratory for Epidemiology, Department of Health Care Management, Chang Gung University, 259, Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, Taiwan. 1142

1143

PREVALENCE OF NOCTURNAL ENURESIS AND ASSOCIATED FAMILIAL FACTORS TABLE 1. Demographic data on the study population No. Enuresis (%)

Odds Ratio

148 (4.31)/251 (7.40)

1/1.72

2,025 (90.73) 1,198 (93.37) 1,044 (95.26) 1,136 (96.93) 1,072 (98.44) 347 (99.43)

207 (9.27) 85 (6.63) 52 (4.74) 36 (3.07) 17 (1.56) 2 (0.57)

1 0.69 0.49 0.31 0.16 0.06

0.0064 0.0001 0.0001 0.0001 0.0001

2,459 (94.69) 4,181 (94.34) 120 (93.02)

138 (5.31) 251 (5.66) 9 (6.98)

1 1.07 1.34

0.5362 0.416

No. No Enuresis (%) Girls/boys 3,432 Age (grade): 7 (1) 8 (2) 9 (3) 10 (4) 11 (5) 12–13 (6) Respondent relationship with child: Father Mother Other * Mantel-Haenszel chi-square test for monotonic trend.

(95.87)/3,393 (93.11)

than 7 years than in the older counterpart 12 to 13 years old (9.27% versus 0.57%, p ⬍0.05). A progressive decrease in enuresis prevalence was observed with increasing age (p ⬍0.05). Enuresis was significantly more common in boys than in girls (7.4% versus 4.31%, odds ratio 1.7, p ⬍0.05). These initial data showed that the nocturnal enuresis prevalence was comparable to that in other western countries. When stratified by the relationship of respondents with study subjects, the prevalence of enuresis was approximately between 5% and 7%. Respondents to this questionnaire were not affected by enuresis, as were the subjects (p ⬎0.05, table 1). Of the recruited subjects 80.6% were living in a family with 2 to 3 children. No significant correlation was established of enuresis prevalence and the number of children in the family, although it is worth mentioning that the lowest risk was associated with a total number of 5 children or greater in a family (odds ratio 0.63, p ⫽ 0.3). Interestingly we also noted that when subject parity in the family was ranked second, the child was at higher risk for enuresis (odds ratio 1.25, p ⬍0.05). In addition, there was a descending order of risk for enuresis as the rank of parity increased from second parity (tables 2 and 3). Parental education level was also documented in the questionnaire. For nonenuretic children who reported parental education 15.6% of fathers (1,024 of 6,554) and 7.2% of mothers (465 of 6,472) attained education at the college level or above. For children with enuresis who reported parental education 19.4% of fathers (75 of 387) and 8.8% of mothers (33 of 375) attained education at the college level or above. Comparatively the ascendants of this group of parents had a higher prevalence than those of a lower father and mother education standard (Mantel-Haenszel chi-square test for trend p ⫽ 0.006 and p ⫽ 0.001, respectively). According to the education level of the trend of the father and mother the odds ratio for enuresis was 1 and 1 for primary school, 1.09 and 1.38 for junior high school, 1.35 and 1.75 for senior high school, and 1.55 and 1.84 for college and above, respectively. Parental raising styles were also analyzed with the prevalence rate. Raising styles were classified into 4 major types, including democratic, authoritarian, permissive and a combination of these styles. Paternal and maternal raising styles were assigned predominately as democratic (each more than 70%) in the study. Although only 11.9% of fathers expressed an authoritarian style, the incidence of enuresis was highest in their children (odds ratio 1.74, p ⫽ 0.0001). Conversely the highest risk of enuresis was also identified in children with a mother who raised her children in a combined style (odds ratio 1.54, p ⫽ 0.0073). The data also showed that more caretaker efforts devoted to children with enuresis were associated with as much as a 3-fold likelihood of enuresis than no efforts at all (p ⫽ 0.0001, table 4). Stratified analyses were performed to examine the interactive effects of parental education levels and raising styles on the risk of children enuresis status. Children with an

p Value 0.001 0.001*

TABLE 2. The relationship of the ordinal number of birth and childhood enuresis

Parity: First Second Third Fourth Fifth Total No. children in family: 1 2 3 4 5 or Greater

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

2,817 (94.75) 2,377 (93.51) 1,215 (95.22) 288 (96.32) 100 (97.09)

156 (5.25) 165 (6.49) 61 (4.78) 11 (3.68) 3 (2.91)

1 1.25 0.91 0.69 0.54

0.0497 0.5266 0.2428 0.3002

335 (95.44) 2,644 (93.99) 2,856 (94.85) 693 (94.29) 234 (97.1)

16 (4.56) 169 (6.01) 155 (5.15) 42 (5.71) 7 (2.9)

1 1.31 1.14 1.27 0.63

0.294 0.6735 0.464 0.2956

p Value

TABLE 3. The relationship of child parity and family size in childhood enuresis Relationship (No. children in family) First: 1 2 3 4 5 or Greater Second: 2 3 4 5 or Greater Third: 3 4 5 or Greater Fourth: 4 5 or Greater Fifth: 5 or Greater

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

p Value

312 (95.41) 1,405 (94.49) 945 (95.55) 110 (93.22) 17 (100)

15 (4.59) 82 (5.51) 44 (4.45) 8 (6.78) 0

1 1.21 0.97 1.51 0

0.5004 0.9166 0.3594

1,240 (93.37) 947 (93.76) 153 (92.73) 32 (94.12)

88 (6.63) 63 (6.24) 12 (7.27) 2 (5.88)

1.48 1.38 1.63 1.3

0.174 0.2703 0.2207 0.7351

973 (95.39) 197 (94.26) 42 (97.67)

47 (4.61) 12 (5.74) 1 (2.33)

1 1.27 0.5

0.9876 0.5519 0.5016

237 (95.95) 48 (97.96)

10 (4.05) 1 (2.04)

0.88 0.43

0.7544 0.4233

0.64

0.4927

97

(97)

3

(3)

authoritarian father were at highest risk for enuresis of all children investigated. Furthermore, there was an increasing trend of childhood risk of enuresis with an increased father education level. Of the children raised according to an authoritarian father raising style the risk of enuresis according to the father education level was 0.63 for primary school, 1.76 for junior high school, 2.54 for senior high school and 2.88 for college or above compared with the reference group of children with a democratic father raising style and primary school education level (table 5). For the effect of mothers the highest risk was observed in children with an authoritarian mother at an education level of senior high school (odds ratio 3.72, p ⫽ 0.0001). Mothers with a combination raising style tended to cause a higher risk

1144

PREVALENCE OF NOCTURNAL ENURESIS AND ASSOCIATED FAMILIAL FACTORS

TABLE 4. The relationship of parental background and raising style to childhood enuresis No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

p Value

Father education: 0.006* Primary school 803 (95.48) 38 (4.52) 1 Junior high school 2,217 (95.11) 114 (4.89) 1.09 0.665 Senior high school 2,510 (94.01) 160 (5.99) 1.35 0.1073 College or above 1,024 (93.18) 75 (6.82) 1.55 0.0328 Mother education: 0.001* Primary school 1,090 (96.29) 42 (3.71) 1 Junior high school 2,214 (94.94) 118 (5.06) 1.38 0.077 Senior high school 2,703 (93.69) 182 (6.31) 1.75 0.0014 College or above 465 (93.37) 33 (6.63) 1.84 0.0106 Father raising style: Democratic 4,960 (94.95) 264 (5.05) 1 Authoritarian 786 (91.5) 73 (8.5) 1.74 0.0001 Permissive 210 (94.17) 13 (5.83) 1.16 0.6058 Combination 543 (93.46) 38 (6.54) 1.31 0.1269 Single parent 104 (99.05) 1 (0.95) 0.18 0.0892 Mother raising style: Democratic 5,176 (94.82) 283 (5.18) 1 Authoritarian 602 (94.21) 37 (5.79) 1.12 0.5158 Permissive 135 (95.74) 6 (4.26) 0.81 0.6232 Combination 582 (92.23) 49 (7.77) 1.54 0.0073 Single parent 124 (92.54) 10 (7.46) 1.47 0.2451 Attention on child care: 0.001 No effort 1,382 (96.37) 52 (3.63) 1 Some effort 4,626 (94.66) 261 (5.34) 1.5 0.0089 Lot of effort 777 (90.14) 85 (9.86) 2.91 0.0001 * Mantel-Haenszel chi-square test for monotonic trend, not including single parent category.

of enuresis in the children. Of the children raised according to a combination mother raising style the risk of enuresis according to mother education level was 3.34 for primary school and 3.59 for senior high school (p ⫽ 0.0029 and 0.0001, respectively). The interactive effects on enuresis in children of the mother raising style and education level became obvious in the democratic category. There was an increasing trend of enuresis in children with an increasing mother education level. The odds ratio was 1 for primary school, 1.62 for junior high school, 1.73 for senior high school and 2.69 for college or above (table 6). In this study the effect of different father and mother raising styles on the children caused a high incidence of enuresis. It was especially true in the families of 1 parent with an authoritarian and the other with a combination style. The odds ratio for enuresis was greater than 4 compared with families with 2 democratic parents (table 7). A higher relative risk of enuresis in children was observed in families with a father with a lower education and a mother with a relatively higher education. When the father had a

primary school education, the odds ratio was as high as 2.83 for the children of a mother with a junior high school education. When the father had a senior high school education and the mother had a college or greater education, the children were at as high as 6.94-fold risk for enuresis compared with those with 2 parents with a primary school education. When the father had a senior high school education, the highest risk for enuresis was observed when the mother had an education level at college or above (table 8). DISCUSSION

This survey of enuresis prevalence had a considerable sample size of 8,997 subjects and a high response rate of 80.3%. The high response rate may imply that childhood health care is a major concern in traditional Chinese culture, which is shared by more than half of the population in Asia. From this survey we learned that nocturnal enuresis is not uncommon in the Taiwanese population. The results indicate that the prevalence of enuresis in Taiwanese children is comparable to that in other regions of the world, such as the United States2 and European countries.3–5 The enuresis prevalence is highest at younger ages (10% at age 6 years) and it decreases progressively as children become older (0.5% at ages greater than 12 years). Moreover, males have enuresis almost twice as often as females (7.4% versus 4.31%). Discrepancies in the Hong Kong study6 and our series may be attributable to the specific westernized culture in Hong Kong, since 100 years ago Hong Kong became a territory of the United Kingdom. On the other hand, Taiwan was occupied by Japan for around 50 years and developed more unique Asian traditions. From the native Chinese or Asian perspective the Taiwanese population may be a more representative source of research samples. There is another way of explaining the discrepancies, such as the small sample size of previous studies. The epidemiological study of enuresis in Korean children showed a higher prevalence rate than our series.7 Traditionally Asian people toilet train children in infancy. Based on the results of Asian studies early toilet training did not alter the process of attaining nocturnal bladder control. These findings favor the opinion of Fergusson et al that the etiology of primary enuresis is mainly biological or maturational factors.8 Although psychological problems have not been shown to be a major cause of nocturnal enuresis,8 the stress perceived by children may be a predisposing factor for this disease.9 In our study familial factors associated with enuresis seemed to be family size, child ranking, and the raising style and education level of the parents. From the current data we were unable to conclude specifically what exactly caused the dis-

TABLE 5. The effect of father raising style and education on childhood enuresis

Father raising style/education: Democratic/primary school Democratic/junior high school Democratic/senior high school Democratic/college or above Authoritarian/primary school Authoritarian/junior high school Authoritarian/senior high school Authoritarian/college or above Permissive/primary school Permissive/junior high school Permissive/senior high school Permissive/college or above Combination/primary school Combination/junior high school Combination/senior high school Combination/college or above Living with mother

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

547 (95.63) 1,636 (95.84) 1,920 (94.67) 768 (93.54) 104 (97.2) 273 (92.54) 276 (89.61) 114 (88.37) 41 (91.11) 88 (95.65) 63 (94.03) 13 (92.86) 62 (95.38) 156 (91.76) 204 (93.15) 114 (95) 102 (99.03)

25 (4.37) 71 (4.16) 108 (5.33) 53 (6.46) 3 (2.8) 22 (7.46) 32 (10.39) 15 (11.63) 4 (8.89) 4 (4.35) 4 (5.97) 1 (7.14) 3 (4.62) 14 (8.24) 15 (6.85) 6 (5) 1 (0.97)

1 0.95 1.231 1.51 0.631 1.763 2.537 2.879 2.135 0.995 1.389 1.683 1.059 1.964 1.609 1.152 0.215

p Value

0.8277 0.3607 0.0979 0.4581 0.06 0.0008 0.002 0.1775 0.9921 0.5534 0.6226 0.9273 0.0511 0.1579 0.7621 0.1333

PREVALENCE OF NOCTURNAL ENURESIS AND ASSOCIATED FAMILIAL FACTORS

1145

TABLE 6. The effect of mother raising style and education on childhood enuresis

Mother education/raising style: Democratic/primary school Democratic/junior high school Democratic/senior high school Democratic/college or above Authoritarian/primary school Authoritarian/junior high school Authoritarian/senior high school Authoritarian/college or above Permissive/primary school Permissive/junior high school Permissive/senior high school Permissive/college or above Combination/primary school Combination/junior high school Combination/senior high school Combination/college or above Living with father

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

790 (96.81) 1,721 (94.93) 2,178 (94.61) 350 (91.86) 133 (97.79) 196 (95.61) 204 (89.08) 47 (100) 41 (93.18) 58 (95.08) 24 (100) 6 (100) 82 (90.11) 176 (95.65) 254 (89.44) 55 (96.49) 124 (92.54)

26 (3.19) 92 (5.07) 124 (5.39) 31 (8.14) 3 (2.21) 9 (4.39) 25 (10.92) 0 3 (6.82) 3 (4.92) 0 0 9 (9.89) 8 (4.35) 30 (10.56) 2 (3.51) 10 (7.46)

1 1.624 1.73 2.691 0.685 1.395 3.724 0 2.223 1.572 0 0 3.335 1.381 3.589 1.105 2.45

p Value

0.032 0.0126 0.0003 0.5403 0.399 0.0001 0.9899 0.205 0.4693 0.9928 0.9964 0.0029 0.4341 0.0001 0.8938 0.0197

TABLE 7. The interactive effects of parental raising style on childhood enuresis Father/Mother Raising Style Democratic/democratic Democratic/authoritarian Democratic/permissive Democratic/combination Authoritarian/democratic Authoritarian/authoritarian Authoritarian/permissive Authoritarian/combination Permissive/democratic Permissive/authoritarian Permissive/permissive Permissive/combination Combination/democratic Combination/authoritarian Combination/permissive Combination/combination

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

4,319 (95.15) 338 (94.15) 30 (96.77) 113 (91.13) 497 (90.86) 191 (95.98) 24 (88.89) 47 (82.46) 78 (92.86) 41 (95.35) 71 (97.26) 12 (92.31) 111 (98.23) 21 (80.77) 3 (100) 390 (93.53)

220 (4.85) 21 (5.85) 1 (3.23) 11 (8.87) 50 (9.14) 8 (4.02) 3 (11.11) 10 (17.54) 6 (7.14) 2 (4.65) 2 (2.74) 1 (7.69) 2 (1.77) 5 (19.23) 0 27 (6.47)

1 1.22 0.65 1.91 1.98 0.82 2.45 4.18 1.51 0.96 0.55 1.64 0.35 4.67 0 1.36

TABLE 8. The interactive effects of parental education on childhood enuresis Father/Mother Education

No. No Enuresis (%)

No. Enuresis (%)

Odds Ratio

407 (97.37) 275 (92.91) 86 (94.51) 5 (100)

11 (2.63) 21 (7.09) 5 (5.49) 0

1 2.83 2.15 0

0.0063 0.1654

418 (96.54) 1,137 (95.07) 570 (95.16) 16 (84.21)

15 (3.46) 59 (4.93) 29 (4.84) 3 (15.79)

1.33 1.92 1.88 6.94

0.4818 0.0504 0.0789 0.0056

216 (93.91) 658 (95.5) 1,443 (93.58) 98 (90.74)

14 (6.09) 31 (4.5) 99 (6.42) 10 (9.26)

2.4 1.74 2.54 3.78

0.0336 0.1191 0.0039 0.0032

p Value 0.001

Primary/primary school Primary/junior high school Primary/senior high school Primary school/college or above Junior high/primary school Junior/junior high school Junior/senior high school Junior high school/college or above Senior high/primary school Senior/junior high school Senior/senior high school Senior high school/college or above College or above/primary school College or above/junior high school College or above/senior high school College or above/college or above

15

(100)

0

0

90 (94.74)

5 (5.26)

2.06

0.1916

554 (92.03)

48 (7.97)

3.21

0.0006

337 (94.4)

20

2.2

0.0398

(5.6)

ease in children. However, subsequent familial stress, followed by these familial factors, is reasonably suspected. They should not be overlooked, especially in a native Asian society. Hence, it is also rational to minimize familial stress for more effective clinical management of nocturnal enuresis. Therapeutic tools, such as enuresis alarms, that augment stress

p Value 0.3985 0.6773 0.0452 0.0001 0.5943 0.1452 0.0001 0.3369 0.9526 0.4109 0.637 0.1471 0.0021 0.1452

within families should be avoided. A previous survey did not show that parental education levels would be related to nocturnal enuresis in their children.3 In addition, other studies have established a higher nocturnal enuresis prevalence with lower parental education level.10 However, our series showed a greater prevalence rate in children with parents of a higher educational status and smaller family size. We cannot explain the disagreement in these studies and ours. Nevertheless, we speculate that highly educated parents in a small family would pay more attention to the health condition of their children and their performance in school. Consequently there are more stresses perceived from the parents, which may induce the enuretic condition in the children. The incidence of nocturnal enuresis would be expected to be higher in children in this type of family. In addition, the higher risk of childhood enuresis in a family with a father with a lower education and a mother with a higher education interests us for further investigation. In addition, the fact that second ranking children in the family had a higher incidence of enuresis may be due to complicated psychosocial mechanisms, which await further investigation. A potential bias of this study is the response bias derived from a few samples in which questions were answered by only 1 parent. Some respondents may have had the chance to discuss and agree with their spouse in regard to parental raising styles. However, some respondents may have answered questions based on their observations without thoroughly confirming with other family members. Since there was no definite answer to which raising style is better in this society, the answer on raising style was less likely to be distorted but criteria may have been different. We anticipate that the misclassification of raising styles was random in the

1146

PREVALENCE OF NOCTURNAL ENURESIS AND ASSOCIATED FAMILIAL FACTORS

group with nocturnal enuresis and controls. Accordingly we may have underestimated the risk of nocturnal enuresis associated with raising style because a nondifferential misclassification bias existed. CONCLUSIONS

This large-scale survey shows a similar prevalence of nocturnal enuresis in the Taiwanese population as in other western countries.2, 3, 9 The results urge the local medical community to view nocturnal enuresis as an international problem that requires immediate attention and management since untreated nocturnal enuresis establishes long-term psychosocial hazards to the patients as well as to their family members.1, 2 Definite therapies incorporated with local considerations should be implemented as soon as the disease is diagnosed.

3.

4.

5.

6.

7.

8.

Steven Chu and Phil Huang assisted with the manuscript. REFERENCES

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Bed-wetting in US children: epidemiology and related behavior problems. Pediatrics, 98: 414, 1996 Spee-van der Wekke, J., Hirasing, R. A., Meulmeester, J. F. and Radder, J. J.: Childhood nocturnal enuresis in The Netherlands. Urology, 51: 1022, 1998 Jarvelin, M. R., Vikevainen-Tervonen, L., Moilanen, I. and Huttunen, N. P.: Enuresis in seven-year-old children. Acta Paediatr Scand, 77: 148, 1988 Collet, J. P., Simore, M. F. and Cochat, P.: [Prevalence of nocturnal enuresis in school-age children.] Pediatrie, 48: 701, 1993 Yeung, C. K.: Nocturnal enuresis in Hong-Kong: different Chinese phenotypes. Scand J Urol Nephrol, suppl., 183: 17, 1997 Lee, S. D., Sohn, D. W., Lee, J. Z., Park, N. C. and Chung, M. K.: An epidemiological study of enuresis in Korean children. BJU Int, 85: 869, 2000 Fergusson, D. M., Horwood, L. J. and Shannon, F. T.: Factors related to the age of attainment of nocturnal bladder control: an 8-year longitudinal study. Pediatrics, 78: 884, 1986 Van Tijen, N. M., Messer, A. P. and Namdar, Z.: Perceived stress of nocturnal enuresis in childhood. Br J Urol, suppl., 81: 98, 1998 Gumus, B., Vurgun, N., Lekili, M., Iscan, A., Muezzinoglu, T. and Buyuksu, C.: Prevalence of nocturnal enuresis and accompanying factors in children aged 7–11 years in Turkey. Acta Paediatr, 88: 1369, 1999