Descriptive epidemiology and correlates of children’s swimming competence

Figures & data

Table 1. Descriptive characteristics of the participants (N = 4959).

					N (%)			Mean (SD)			95% CI
Demographic Information
Age								8.63 (1.71)			8.58–8.68
Sex
Female					2705 (54.69%)
Male					2241 (45.31%)
School Grade
Primary 1					913 (18.42%)
Primary 2					796 (16.06%)
Primary 3					888 (17.91%)
Primary 4					1032 (20.82%)
Primary 5					662 (13.35%)
Primary 6					666 (13.44%)
Parent highest education level
Secondary or lower					1410 (44.42%)
Post-school training college					421 (13.26%)
University (undergraduate)					768 (24.20%)
University (postgraduate)					575 (18.12%)
Family income
Low (≤ HKD $15,000)					500 (27.58%)
Middle (HKD $15,000 – HKD $39,999)					672 (37.07%)
High (≥ HKD $40,000)					641 (35.36%)
Swimming Experience
Age to start learning swimming								6.12 (1.77)			6.06–6.18
Years of swimming								2.79 (1.99)			2.72–2.85
Frequency of swimming (times per month)								2.88 (3.25)			2.77–2.99
Duration of swimming (mins per session)								74.92 (37.23)			73.76–76.08
Winter swimming					1177 (25.87%)
Swimming Location
Public swimming pools					3343 (67.41%)
School swimming pools					561 (11.31%)
Club swimming pools					1315 (26.52%)
Estate swimming pools					1464 (29.52%)
Beaches					1564 (31.54%)
Swimming Accessibility
Public swimming pools					2535 (51.12%)
School swimming pools					437 (8.81%)
Club swimming pools					1013 (40.43%)
Estate swimming pools					1216 (24.52%)
Beaches					514 (10.36%)
Learning Experience
Parent/guardian					1902 (38.35%)
Swimming club					1346 (27.14%)
Government class					1302 (26.26%)
Private coach					1223 (24.66%)
School/PE teacher					431 (8.69%)
Sibling					260 (5.24%)
Friend					204 (4.11%)
Relative					203 (4.09%)
Grandparent					114 (2.30%)
Non-Fatal Aquatic Event					2046 (41.26%)
Cuts/bruises					779 (38.07%)
Out of breath					422 (20.63%)
Fatigue					415 (20.28%)
Non-fatal drowning					377 (18.43%)
Muscle cramp					344 (16.81%)
Anxiety/panic					155 (7.58%)
Swimming Competence Index								45.86 (32.76)			44.87–46.85
Maximum Swimming Distance	General		Front-crawl			Breaststroke			Backstroke			Butterfly
Very Weak (0 m – 4.99 m)	37.15%		47.55%			50.71%			65.30%			80.71%
Weak (5 m – 12.49 m)	8.89%		6.73%			6.03%			3.40%			2.12%
Beginner (12.5 m – 24.99 m)	8.16%		6.35%			5.75%			3.57%			1.56%
Intermediate (25 m – 49.99 m)	13.98%		11.99%			10.73%			7.57%			5.39%
Good (50 m – 99.99 m)	14.72%		12.35%			12.55%			9.84%			5.24%
Excellent (>100 m)	17.09%		15.02%			14.24%			10.33%			4.98%
Mean Distance [95% CI]	67.63 m [63.02–72.14]		58.41 m [54.59–62.44]			50.59 m [47.37–54.51]			32.05 m [29.79–34.29]			13.17 m [11.99–14.32]
Swimming Skills	Poolside Kicking		Kicking With Kickboard			Holding Breath Underwater		Floating		Treading Water			Swimming Underwater
Able	87.69%		81.23%			81.35%		61.86%		56.79%			50.51%
Not Able	12.31%		18.77%			18.65%		38.14%		43.21%			49.49%

Note. SD = standard deviation, CI = bias-corrected and accelerated bootstrap confidence interval. PE teacher = physical education teacher. Maximum swimming distance indicates the maximum distance participants could swim without any assistance or rest. “General” indicates the maximum swimming distance by any stroke or combination of strokes. Mean Distance = Mean swimming distance in metres.

Figure 1a-e. Maximum swimming distance by stroke and sex. Error bars represent bias-corrected and accelerated bootstrap confidence intervals.

Table 2. Results of hierarchical linear multiple regression models.

Dependent Variable = Swimming Competence
Step	Independent Variables	β	95% CI of B	F	ΔF	R^2	ΔR^2	VIF
Demographic Factors
1	Age	.31**	4.46–5.84	96.24**	N/A	.28	N/A	1.54
	Sex	.04*	.01–4.38					1.01
	Parents’ highest education	.15**	3.02–5.30					1.03
	Family Income	.14**	1.08–1.90					1.04
Swimming Experience
2	Years of swimming	.32**	3.68–4.75	257.80**	360.62**	.47	.33	1.53
	Frequency of swimming	.23**	1.60–2.14					1.01
	Swimming duration	.03	.00 –.05					1.06
	Winter swimming	.30**	14.78–18.97					1.02
Swimming Location
2	Public swimming pool	.14**	7.83–11.900	188.17**	104.54**	.28	.09	1.03
	School swimming pool	.25**	22.34–27.52					1.06
	Club swimming pool	.14**	8.53–12.54					1.09
	Estate swimming pool	.08**	3.77–7.82					1.05
	Beach	−.03*	−3.90 – −.27					1.01
Swimming Accessibility
2	Public swimming pool	.12**	6.00–9.59	164.76**	70.66**	.26	.06	1.03
	School swimming pool	.17**	16.13–22.03					1.05
	Club swimming pool	.13**	8.20–12.14					1.07
	Estate swimming pool	.07	3.57–7.54					1.06
	Beach	−.02	−5.38 – −.03					1.01
Learning Experience
2	Parent/guardian	−.03**	−3.77 – −.72	233.47**	179.00**	.43	.24	1.01
	Swimming club	.38**	25.46–28.79					1.02
	Government class	.21**	13.81–17.26					1.01
	Private coach	.31**	21.56–25.34					1.06
	School/PE teacher	.08**	5.62–11.29					1.03
	Grandparent	−.00	−5.29–4.88					1.00
	Relative	−.01	−5.68–1.61					1.01
	Sibling	.01	−.97–5.33					1.01
	Friend	−.01	−5.91–1.71					1.01

Note. Step 1 was identical throughout the three models. CI of B = 95% bias-corrected and accelerated bootstrap confidence interval of unstandardized beta. VIF = variance inflation factor. Swimming duration = duration of each swimming session in minutes. Learning experience = “Learn swimming from whom?”. PE teacher = physical education teacher. *p <.05; **p <.01.

Table 3. Results of hierarchical logistic regression models.

Dependent Variable = Non-Fatal Events
Step	Variables	Odds Ratio	95% CI of EXP (B)	Wald	χ^2	R^2	ΔR^2
Demographic Factors
1	Age	1.26**	1.18–1.34	49.05	89.06**	.047	N/A
	Sex	.86	.73–1.02	3.19
	Parents’ highest education	.92	.83–1.01	3.14
	Family income	.99	.96–1.03	.18
Swimming Experience
2	Years of swimming	.98	.93–1.01	.87	103.42**	.055	.008
	Frequency of swimming	1.00	.98–1.03	.09
	Swimming duration	1.01**	1.00–1.01	10.71
	Winter swimming	1.12	.93–1.35	1.33
Swimming Competence
3	General	.99	.87–1.13	.02	120.61**	.064	.017
	Breaststroke	.97	.89–1.06	.34
	Front-crawl	.99	.90–1.09	.02
	Backstroke	1.06	.98–1.14	2.17
	Butterfly	1.05	.98–1.12	1.54
	Swimming underwater	.87	.72–1.07	1.78
	Floating	1.04	.70–1.55	.03
	Poolside kicking	.96	.75–1.22	.13
	Kickboard kicking	1.21	.72–2.03	.52
	Holding breath underwater	1.14	.77–1.70	.41
	Treading water	.77**	.63 –.95	5.93
Swimming Location
3	Public swimming pool	1.09	.91–1.32	.85	113.71**	.058	.011
	School swimming pool	1.12	.92–1.36	1.29
	Club swimming pool	1.17	.93–1.47	1.70
	Estate swimming pool	1.06	.88–1.27	.36
	Beach	1.12	.94–1.34	1.67
Swimming Accessibility
3	Public swimming pool	1.13	.95–1.33	1.86	111.46**	.057	.010
	School swimming pool	1.23	.96–1.57	2.59
	Club swimming pool	.98	.81–1.19	.03
	Estate swimming pool	1.14	.95–1.37	1.96
	Beach	.94	.73–1.22	.21
Learning Experience
3	Parent/guardian	1.18	.99–1.40	3.39	131.23**	.067	.020
	Swimming club	1.19	.98–1.45	3.24
	Government class	1.08	.90–1.30	.65
	Private coach	1.06	.88–1.27	.33
	School/PE teacher	1.53**	1.18–1.98	1.09
	Grandparent	1.18	.69–2.02	.37
	Relative	1.39	.90–2.15	2.18
	Sibling	1.28	.88–1.84	1.70
	Friend	1.09	.71–1.68	.17

Note. Controls are age, gender, grade, parents’ education, income and years, frequency, duration of swimming and winter swimming. Steps 1 and 2 were identical throughout the three models. R² = Nagelkerke R-squared. 95% CI of EXP (B) = 95% confidence interval of the odds ratio. Learning experience = “Learn swimming from whom?”. PE teacher = physical education teacher.

*p <.05; **p <.01.

Maximum swimming distance by sex and school grade.

		General	Front-crawl	Breaststroke	Backstroke	Butterfly
Sex
	Male (N = 2241; M-age = 8.49)	72.81 m [65.43–80.20]	62.88 m [55.43–70.26]	54.67 m [48.42–61.16]	33.05 m [28.15–37.88]	13.63 m [11.74–15.56]
	Female (N = 2705 M-age = 8.06)	63.5 m [57.06–70.18]	54.83 m [49.15–61.35]	47.99 m [43.16–53.17]	31.28 m [28.22–34.74]	12.81 m [11.30–14.36]
School Grade
	Primary 1 (N = 913; M-age = 6.17)	16.63 m [12.39–23.62]	15.06 m [10.97–21.12]	11.86 m [8.34– 16.98]	8.05 m [5.43– 11.65]	2.22 m [1.12– 3.69]
	Primary 2 (N = 796; M-age = 6.99)	46.39 m [40.41–51.92]	41.17 m [35.40–46.79]	31.67 m [27.31–36.44]	20.52 m [17.43–23.55]	7.23 m [5.86– 8.54]
	Primary 3 (N = 888; M-age = 8.31)	51.53 m [39.31–65.81]	45.96 m [33.51–61.15]	39.22 m [30.47–49.77]	27.01 m [20.67–34.49]	9.77 m [7.07–12.54]
	Primary 4 (N = 1032; M-age = 9.27)	71.73 m [64.44–78.40]	60.88 m [54.22–67.26]	53.51 m [48.00–58.63]	32.16 m [25.43–41.09]	13.47 m [10.22–16.93]
	Primary 5 (N = 662; M-age = 10.29)	114.26 m [103.03–125.91]	100.78 m [89.81–111.94]	89.2 m [79.69–98.86]	56.38 m [44.17–68.85]	25.11 m [19.16–32.24]
	Primary 6 (N = 666 M-age = 11.14)	131.71 m [119.50–143.82]	109.07 m [97.78–120.70]	101.22 m [91.13–111.69]	61.02 m [54.47–67.80]	27.34 m [23.99–30.87]

Note. Values are mean (95% bias-corrected and accelerated bootstrap confidence interval). Maximum swimming distance indicates the maximum swimming distance participants could swim without any assistance or rest. “General” indicates the maximum swimming by any stroke or combination of strokes. M-age = mean age of the category.

Swimming skills by sex and school grade.

Swimming Skills		Poolside Kicking	Kicking With Kickboard	Holding Breath Underwater	Floating	Treading Water	Swimming Underwater
Sex
Male	Able	1817 (81.08%)	1684 (75.15%)	1716 (76.57%)	1262 (56.31%)	1173 (52.34%)	1052 (46.94%)
	Not Able	424 (18.92%)	557 (24.86%)	525 (23.43%)	979 (43.69%)	1068 (47.66%)	1189 (53.06%)
Female	Able	2298 (84.95%)	2117 (78.26%)	2121 (78.41%)	1587 (58.67%)	1443 (53.35%)	1276 (47.17%)
	Not Able	407 (15.05%)	588 (21.74%)	584 (21.59%)	1118 (41.33%)	1262 (46.65%)	1429 (52.83%)
School Grade
Primary 1	Able	637 (69.77%)	551 (60.35%)	511 (55.97%)	311 (34.06%)	274 (30.01%)	224 (24.54%)
	Not Able	276 (30.23%)	362 (39.65%)	402 (44.03%)	602 (65.94%)	639 (69.99%)	689 (75.47%)
Primary 2	Able	648 (81.41%)	615 (77.26%)	592 (74.37%)	422 (53.02%)	368 (46.23%)	295 (37.06%)
	Not Able	148 (18.59%)	181 (22.74%)	204 (25.63%)	374 (46.90%)	428 (53.77%)	501 (62.94%)
Primary 3	Able	738 (83.11%)	683 (76.91%)	701 (78.94%)	486 (54.73%)	443 (49.89%)	414 (46.62%)
	Not Able	150 (16.89%)	205 (23.09%)	187 (21.06%)	402 (45.27%)	445 (50.11%)	474 (53.38%)
Primary 4	Able	884 (85.66%)	826 (80.04%)	837 (81.11%)	637 (61.73%)	589 (57.07%)	536 (51.94%)
	Not Able	148 (14.34%)	206 (19.96%)	195 (18.90%)	395 (38.28%)	443 (42.93%)	496 (48.06%)
Primary 5	Able	598 (90.33%)	558 (84.29%)	594 (89.73%)	489 (73.87%)	472 (71.30%)	428 (64.65%)
	Not Able	64 (9.67%)	104 (15.71%)	68 (10.27%)	173 (26.13%)	190 (28.70%)	234 (35.35%)
Primary 6	Able	616 (92.49%)	573 (86.04%)	605 (90.84%)	507 (76.13%)	473 (71.02%)	430 (64.56%)
	Not Able	50 (7.51%)	93 (13.96%)	61 (9.16%)	159 (23.87%)	193 (28.98%)	236 (35.44%)

Note. Values are N (%).

Swimming competence index by sex and school grade.

		Swimming Competence Index
Sex
	Male	45.74 [44.33–47.22]
	Female	45.99 [44.49–47.68]
School Grade
	Primary 1	24.18 [22.43–26.05]
	Primary 2	39.40 [37.06–41.90]
	Primary 3	43.83 [41.36–46.21]
	Primary 4	48.81 [46.70–50.92]
	Primary 5	61.75 [59.47–64.36]
	Primary 6	61.53 [59.99–64.18]

Note. Values are mean (95% bias-corrected and accelerated bootstrap confidence interval).