Relationship between daylength and suicide in Finland

Laura Hiltunen; Kirsi Suominen; Jouko Lönnqvist; Timo Partonen

doi:10.1186/1740-3391-9-10

Figures & Tables

Table 1

Men's suicides in numbers during the study period

	Oulu			Helsinki			Finland
Year	Men	S	per 100 000	Men	S	per 100 000	Men	S	per 100 000
1969	42 447	11	25.92	272 321	110	40.39	2 230 217	850	38.11
1970	41 412	13	31.39	266 174	108	40.58	2 219 985	763	34.37
1971	42 798	11	25.70	271 393	117	43.11	2 234 037	781	34.96
1972	43 436	22	50.65	275 378	132	47.93	2 249 051	874	38.86
1973	44 127	27	61.19	277 205	109	39.32	2 262 142	849	37.53
1974	45 082	22	48.80	278 485	131	47.04	2 273 815	921	40.51
1975	45 815	22	48.02	278 628	128	45.40	2 282 115	924	40.49
1976	46 069	29	62.95	278 693	152	54.54	2 286 392	967	42.29
1977	46 444	22	47.37	277 978	154	55.40	2 295 668	962	41.91
1978	46 609	13	27.89	277 735	156	56.17	2 300 790	963	41.86
1979	46 533	18	38.68	278 569	133	47.74	2 306 784	935	40.53
1980	46 779	24	51.31	279 456	145	51.89	2 314 843	962	41.56
1981	47 343	21	44.36	280 580	151	53.82	2 327 473	904	38.84
1982	48 179	18	37.36	282 751	134	47.39	2 342 869	905	38.63
1983	48 331	25	51.73	284 565	130	45.68	2 357 172	938	39.79
1984	48 620	25	51.42	286 092	149	52.08	2 369 228	988	41.70
1985	49 065	23	46.88	287 858	113	39.26	2 377 780	964	40.54
1986	49 405	30	60.72	290 370	149	51.31	2 385 866	1023	42.88
1987	49 890	28	56.12	292 935	137	46.77	2 392 868	1068	44.63
1988	50 138	44	87.76	294 242	150	50.98	2 401 368	1112	46.31
1989	50 951	29	56.92	295 665	160	54.12	2 412 760	1121	46.46
1990	51 623	33	63.93	298 420	198	66.35	2 426 204	1199	49.42
1991	52 254	35	66.98	302 609	185	61.14	2 443 042	1193	48.83
1992	52 959	36	67.98	306 298	204	66.60	2 457 282	1160	47.21
1993	53 495	35	65.43	311 134	172	55.28	2 470 196	1112	45.02
1994	54 661	23	42.08	316 367	176	55.63	2 481 649	1080	43.52
1995	56 132	26	46.32	322 074	179	55.58	2 491 701	1081	43.38
1996	57 436	26	45.27	327 168	131	40.04	2 500 596	966	38.63
1997	58 482	36	61.56	332 113	158	47.57	2 509 098	1039	41.41
1998	59 606	26	43.62	337 297	121	35.87	2 516 075	965	38.35
1999	61 025	40	65.55	341 125	139	40.75	2 523 026	961	38.09
2000	62 800	28	44.59	344 520	143	41.51	2 529 341	879	34.75
2001	64 116	31	48.35	347 925	150	43.11	2 537 597	936	36.89
2002	64 995	22	33.85	349 121	139	39.81	2 544 916	825	32.42
2003	65 965	29	43.96	350 334	119	33.97	2 552 893	823	32.24

The yearly male population, number of suicides(S), and suicide mortality for men in Oulu, Helsinki, and Finland from 1969 to 2003.

Table 2

Women's suicides in numbers during the study period

	Oulu			Helsinki			Finland
Year	Women	S	per 100 000	Women	S	per 100 000	Women	S	per 100 000
1969	46 245	5	10.81	333 502	43	12.89	2 384 060	246	10.32
1970	45 656	4	8.76	325 034	58	17.84	2 378 351	220	9.25
1971	46 474	5	10.76	330 205	58	17.57	2 391 875	222	9.28
1972	47 633	5	10.50	333 507	57	17.09	2 404 350	239	9.94
1973	48 302	6	12.42	335 687	60	17.87	2 416 619	249	10.30
1974	49 272	11	22.33	337 470	47	13.93	2 428 572	255	10.50
1975	50 132	5	9.97	337 570	72	21.33	2 438 377	254	10.42
1976	50 410	12	23.81	336 980	66	19.59	2 444 444	253	10.35
1977	50 691	8	15.78	335 057	54	16.12	2 451 299	258	10.53
1978	50 964	11	21.58	334 547	53	15.84	2 457 298	237	9.65
1979	51 188	6	11.72	334 981	60	17.91	2 464 508	242	9.82
1980	51 582	4	7.76	335 630	63	18.77	2 472 935	264	10.68
1981	52 237	1	1.91	336 511	56	16.64	2 484 677	239	9.62
1982	53 059	10	18.85	338 116	59	17.45	2 498 846	267	10.69
1983	53 225	6	11.27	339 108	56	16.51	2 512 686	249	9.91
1984	53 443	3	5.61	340 162	54	15.88	2 524 520	253	10.02
1985	53 976	4	7.41	341 781	58	16.97	2 532 884	249	9.83
1986	54 349	12	22.08	343 576	53	15.43	2 539 778	287	11.30
1987	54 760	10	18.26	346 162	65	18.78	2 545 734	301	11.82
1988	55 125	9	16.33	346 880	62	17.87	2 552 991	296	11.59
1989	55 810	8	14.33	347 226	58	16.70	2 561 623	297	12.59
1990	56 294	8	14.21	348 913	90	25.79	2 572 274	324	11.60
1991	56 735	8	14.10	352 207	74	21.01	2 585 960	306	11.83
1992	57 391	6	10.46	354 429	77	21.73	2 597 700	297	11.43
1993	57 765	6	10.39	358 557	72	20.08	2 607 716	293	11.24
1994	58 781	12	20.42	363 774	77	21.17	2 617 105	307	11.73
1995	60 186	12	19.94	369 437	65	17.59	2 625 125	309	11.77
1996	61 447	8	13.02	373 663	69	18.47	2 631 724	282	10.72
1997	62 439	11	17.62	378 547	68	17.96	2 638 251	284	10.77
1998	63 454	11	17.34	382 880	57	14.89	2 643 571	268	10.14
1999	64 516	13	20.15	386 384	68	17.60	2 648 276	254	9.59
2000	66 149	11	16.63	389 425	66	16.95	2 651 774	292	11.01
2001	67 584	9	13.32	391 649	62	15.83	2 657 304	271	10.20
2002	68 297	11	16.11	392 485	48	12.23	2 661 379	275	10.33
2003	68 878	7	10.16	393 035	55	13.99	2 666 839	261	9.79

The yearly female population, number of suicides(S), and suicide mortality for women in Oulu, Helsinki, and Finland from 1969 to 2003.

**Periods according to time of equation and astronomical seasons**. During X1(February 11-May 04) and X2 (July 26-November 03) (marked with pink lines) sun time is accelerating, and during Y1 (May 15-July25) and Y2 (November 04-February 10) (marked with green lines) it is decelerating compared with the coordinated universal time (UCT). During A1 (April 15-June13) and A2 (September 01-December 25) sun time stays ahead and during D1 (June 14-August 31) and D2 (December 26-April 14) it stays behind the UCT. Astronomical seasons are separated with dotted vertical lines. During astronomical spring and summer daylight exceeds darkness, and vice versa during astronomical fall and winter darkness exceeds daylight in Finland. Y-axis on the left side presents the time difference (in minutes) that sun time deviates from the UCT.

Table 3

Astronomical seasons and men's (M) and women's (W) suicide mortality

	Area	Selected Days		Astronomical season
				Winter	Spring	Summer	Fall
M	Finland	All		.099 .094-.103	.120 .115-.125	.117 .112-.122	.106 .101-.111
	Helsinki	All		.128 .120-.136	.138 .128-.148	.135 .123-.147	.131 .122-.140
		T+	S+	.123 .099-.146	.135 .122-.147	.139 .122-.156	.137 .120-.155
			S-	.113 .092-.134	.144 .125-.163	.142 .120-.164	.115 .099-.132
		T-	S+	.122 .108-.136	.146 .128-.163	.130 .117-.143	.133 .118-.147
			S-	.122 .097-.146	.140 .120-.161	.129 .112-.146	.144 .116-.172
	Oulu	All		.119 .098-.140	.141 .123-.160	.159 .138-.180	.131 .113-.150
		T+	S+	.107 .050-.163	.134 .103-.165	.162 .112-.212	.152 .077-.227
			S-	.097 .059-.135	.126 .082-.170	.175 .132-.217	.147 .101-.193
		T-	S+	.124 .094-.154	.167 .132-.203	.156 .115-.197	.117 .073-.161
			S-	.097 .045-.148	.138 .110-.166	.132 .086-.178	.144 .083-.205
W	Finland	All		.025 .023-.027	.031 .030-.032	.029 .028-.031	.028 .027-030
	Helsinki	All		.046 .042-.050	.050 .045-.054	.049 .045-.054	.048 .043-.053
		T+	S+	.038 .028-.048	.056 .046-.065	.049 .039-.058	.056 .043-.069
			S-	.051 .033-.069	.049 .041-.056	.046 .034-.058	.052 .042-.062
		T-	S+	.042 .036-.049	.046 .034-.057	.049 .040-.057	.049 .039-.059
			S-	.052 .039-.065	.052 .042-.062	.051 .041-.061	.045 .031-.059
	Oulu	All		.036 .029-.044	.040 .030-.049	.042 .032-.051	.039 .029-.048
		T+	S+	.032 .006-.058	.031 .016-.046	.042 .023-.061	.049 .013-.086
			S-	.037 .015-.058	.030 .015-.043	.047 .020-.074	.020 .005-.036
		T-	S+	.041 .019-.063	.051 .028-.074	.037 .019-.055	.043 .019-.067
			S-	.028 .000-.055	.045 .020-.069	.042 .020-.063	.047 .018-.076

Daily mean of suicide mortality and confidence interval of the mean in aggregate over the years from 1969 to 2003 for men and women, during astronomical seasons in Finland, Helsinki and Oulu, and according to daily changes (+/-) in temperature (T) and sunshine hours(S) in Helsinki and Oulu.

Winter: 21.12-20.03

Spring: 21.03-20.06

Summer: 21.06-22.09

Fall: 23.09-20.12

Table 4

Accelerating and decelerating periods of the equation of time and men's (M) and women's (W) suicide mortality

	Area	Selected Days		Periods of time of equation
				X1	Y1	X2	Y2
M	Finland	All		.109 .105-.114	.124 .118-.129	.112 .107-.116	.101 .096-.106
	Helsinki	All		.131 .121-.141	.142 .130-.154	.130 .122-.139	.130 .120-.140
		T+	S+	.139 .116-.161	.149 .131-.167	.122 .097-.147	.124 .097-.151
			S-	.151 .123-.179	.145 .119-.170	.124 .103-.145	.110 .088-.131
		T-	S+	.152 .122-.182	.126 .100-.153	.135 .121-.150	.120 .099-.141
			S-	.133 .104-.161	.124 .106-.142	.138 .116-.160	.114 .086-.142
	Oulu	All		.133 .115-.150	.146 .124-.167	.150 .131-.169	.122 104-.140
		T+	S+	.156 .094-.218	.149 .101-.198	.206 .122-.290	.131 .052-.210
			S-	.096 .042-.150	.207 .142-.272	.165 .112-.217	.097 .046-.148
		T-	S+	.199 .138-.259	.140 .090-.190	.138 .092-.184	.115 .068-.162
			S-	.123 .065-.181	.158 .114-.201	.175 .107-.242	.056 .008-.103
W	Finland	All		.028 .027-.029	.032 .030-.033	.030 .029-.031	.025 .024-.027
	Helsinki	All		.047 .043-.051	.053 .048-.058	.050 .045-.054	.043 .039-.048
		T+	S+	.052 .040-.064	.055 .046-.065	.056 .044-.068	.033 .018-.048
			S-	.044 .030-.057	.059 .047-.072	.055 .041-.069	.055 .044-.067
		T-	S+	.051 .032-.070	.049 .036-.061	.049 .040-.058	.036 .028-.045
			S-	.051 .034-.067	.046 .034-.058	.048 .037-.058	.045 .025-.065
	Oulu	All		.038 .029-.047	.045 .034-.057	.035 .027-.042	.038 .029-.047
		T+	S+ S-	.023 .005-.042	.039 .017-.060	.044 .014-.074	-
				.035 .012-.058	.053 .018-.087	.015 .001-.029	.026 .002-.050
		T-	S+ S-	.062 .028-.096	.030 .006-.054	.042 .024-.061	.036 .013-.059
				.030 .003-.058	.060 028-.091	.032 .010-.054	-

Daily mean of suicide mortality and confidence interval of the mean in aggregate over the years from 1969 to 2003 for men and women, during accelerating (X1, X2) and decelerating (Y1, Y2) periods of the equation of time in Finland, Helsinki and Oulu, and according to daily changes (+/-) in temperature (T) and sunshine hours(S) in Helsinki and Oulu.

X1: 11.02-14.05

Y1: 15.05-25.07

X2: 26.07-03.11

Y2: 04.11-10.2

Table 5

Advanced and delayed periods of the equation of time and men's (M) and women's (W) suicide mortality

	Area	Selected days		Periods of time of equation
				D2	A1	D1	A2
M	Finland	All		.102 .098-.107	.125 .120-.130	.118 .112-.123	.107 .102-.111
	Helsinki	All		.128 .121-.136	.146 .134-.158	.135 .122-.147	.130 .122-.139
		T+	S+	.125 .103-.146	.142 .129-.154	.141 .123-.159	.128 .108-.148
			S-	.123 .102-.143	.142 .119-.164	.145 .121-.169	.116 .100-.131
		T-	S+	.124 .111-.136	.162 .137-.187	.124 .108-.141	.134 .121-.146
			S-	.123 .103-.144	.147 .124-.171	.126 .110-.142	.141 .118-.164
	Oulu	All		.125 .107-.144	.145 .123-.167	.148 .128-.168	.139 .119-.159
		T+	S+	.099 .059-.139	.159 .123-.196	.137 .088-.185	.186 .121-.250
			S-	.105 .065-.145	.129 .080-.178	.177 .129-.225	.150 .104-.196
		T-	S+	.140 .112-.168	.155 .103-.208	.146 .095-.197	.129 .090-.168
			S-	.109 .062-.157	.137 .097-.176	.122 .079-.165	.149 .091-.206
W	Finland	All		.026 .024-.027	.032 .030-.034	.030 .028-.031	.028 .027-.030
	Helsinki	All		.046 .042-.049	.051 .045-.056	.051 .046-.056	.048 .043-.053
		T+	S+	.043 .034-.053	.058 .047-.069	.048 .039-.057	.056 .047-.065
			S-	.050 .033-.067	.047 .033-.062	.049 .038-.061	.052 .042-.062
		T-	S+	.041 .034-.048	.051 .036-.066	.050 .040-.061	.048 .040-.056
			S-	.048 .039-.058	.057 .044-.069	.051 .040-.062	.048 .037-.059
	Oulu	All		.036 .029-.044	.043 .032-.054	.041 .030-.053	.038 .031-.048
		T+	S+	.037 .016-.059	.031 .013-.050	.036 .017-.054	.044 .019-.069
			S-	.033 .016-.049	.033 .013-.054	.058 .024-.092	.017 .005-.030
		T-	S+	.045 .026-.063	.047 .020-.075	.040 .014-.066	.040 .022-.058
			S-	.025 .002-.048	.053 .021-.085	.041 .019-.064	.039 .020-.057

Daily mean of suicide mortality and confidence interval of the mean, in aggregate over the years from 1969 to 2003 for men and women, during advanced (A1, A2) and delayed (D1, D2) periods of the equation of time in Finland, Helsinki and Oulu, and according to daily changes (+/-) in temperature (T) and sunshine hours(S) in Helsinki and Oulu.

A1: 15.04-13.06

D1: 14.06-31.08

A2: 01.09-25.12

D2: 26.12-14.04

Table 6

Men: Daily mean of suicide mortality, and switching into daylight saving time in spring.

	Days	1969-80*				1981-2003
		-1 m		+1 m		-1 m		+1 m
		M	CI	m	CI	m	CI	m	CI
Finland	All	.097	.089-.106	.111	.102-.121	.104	.097-.111	.117	.110-.124
Helsinki	All	.114	.096-.133	.130	.114-.146	.135	.120-.150	.137	.118-.155
	T+S+	.120	.061-.180	.160	.100-.219	.129	.084-.173	.140	.102-.177
	T+S-	.100	.054-.146	.156	.100-.212	.128	.084-.171	.181	.143-.220
	T-S+	.123	.090-.156	.102	.067-.137	.139	.108-.171	.142	.100-.184
	T-S-	.144	.044-.243	.127	.061-.194	.180	.114-.246	.108	.080-.136
Oulu	All	.113	.064-.162	.114	.060-.168	.121	.092-.150	.158	.117-.199
	T+S+	-	-	-	-	-	-	.110	.042-.179
	T+S-	-	-	-	-	.145	.060-.229	.146	.055-.237
	T-S+	.123	.037-.208	.152	.013-.291	.104	.038-.171	.21	.139-.280
	T-S-	-	-	-	-	.065	.002-.129	.138	.039-.237

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch into daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Table 7

Women: Daily mean of suicide mortality and switching into daylight saving time in spring.

Location	Days	1969-80 *				1981-2003(DST1 + DST2)
		-1 m		+1 m		-1 m		+1 m
		m	CI	m	CI	m	CI	m	CI
Finland	All	.024	.020-.028	.026	.023-.029	.027	.024-.030	.030	.027-.033
Helsinki	All	.055	.048-.062	.043	.031-.055	.043	.034-.052	.049	.040-.059
	T+S+	.042	.014-.071	.052	.020-.083	.047	.019-.076	.055	.035-.076
	T+S-	.054	.028-.080	.031	.010-.052	.024	.012-.037	.046	.030-.062
	T-S+	.061	.041-.081	.029	.004-.053	.040	.022-.057	.065	.028-.101
	T-S-	.052	.018-.087	-	-	.049	.020-.079	.044	.024-.065
Oulu	All	.033	.006-.059	.048	.016-.080	.048	.030-.066	.030	.009-.050
	T+S+	-	-	-	-	-	-	-	-
	T+S-	-	-	-	-	.053	.013-.094	-	-
	T-S+	-	-	-	-	.067	.018-.117	-	-
	T-S-	-	-	-	-	-	-	-	-

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch into daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Table 8

Men: Daily mean of suicide mortality, and switching away from daylight saving time in fall.

Location	Days	1969-80*				1981-94 (DST1)
		-1 m		+1 m		-1 m		+1 m
		m	CI	m	CI	m	CI	m	CI
Finland	All	.111	.099-.122	.101	.094-.108	.119	.109-.128	.120	.112-.128
Helsinki	All	.141	.106-.177	.120	.104-.137	.139	.125-.153	.140	.122-.158
	T+S+	.151	.064-.238	.115	.078-.151	.091	.039-.143	.163	.107-.219
	T+S-	.156	.076-.236	.107	.048-.166	.124	.087-.161	.123	.079-.167
	T-S+	.137	.089-.185	.132	.083-.182	.156	.115-.197	.144	.107-.180
	T-S-	.138	.087-.189	.147	.085-.208	.184	.125-.244	.155	.062-.248
Oulu	All	.114	.060-.168	.125	.092-.158	.239	.165-.313	.121	.067-.175
	T+S+	-	-	-	-	.324	.113-.535	-	-
	T+S-	.100	.001-.200	.107	.002-.211	.256	.053-.458	.110	.000-.220
	T-S+	.189	.084-.295	.130	.024-.237	.182	.060-.303	.103	.029-.176
	T-S-	-	-	-	-	.267	.142-.392	.229	.065-.393

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch away daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Table 9

Women: Daily mean of suicide mortality, and switching away from daylight saving time in fall.

Location	Days		1969-80 *				1981-94 (DST1)
			-1 m		+1 m		-1 m		+1 m
			m	CI	m	CI	m	CI	m	CI
Finland	All		.028	.025-.032	.029	.026-.033	.029	.024-.033	.035	.031-.039
Helsinki	All		.052	.039-.064	.048	.033-.062	.046	.030-.061	.064	.049-.078
	T+	S+	.071	.045-.097	.039	.019-.058	-	-	.074	.040-.108
		S-	-	-	.069	.033-.104	.049	.015-.084	.058	.033-.083
	T-	S+	.049	.025-.073	.055	.021-.089	.052	.031-.073	.067	.038-.096
		S-	.070	.022-.118	.023	.001-.046	.032	.005-.059	.065	.026-.103
Oulu	All		.033	.011-.055	.043	.006-.081	.020	.001-.040	.024	.001-.047
	T+S+		-	-	-	-	-	-	-	-
	T+S-		-	-	-	-	-	-	-	-
	T-S+		-	-	-	-	-	-	-	-
	T-S-		-	-	-	-	-	-	-	-

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch away daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Table 10

Men: Daily mean of suicide mortality, and switching away from daylight saving time in fall.

Location	Days	1969-80*				1995-2003 (DST2)
		-1 m		+1 m		-1 m		+1 m
		m	CI	m	CI	m	CI	m	CI
Finland	All	.101	.094-.108	.101	.093-.110	.105	.095-.115	.097	.088-.105
Helsinki	All	.126	.108-.145	.140	.119-.161	.118	.079-.157	.106	.090-.121
	T+S+	.116	.073-.159	.181	.078-.285	.128	.045-.212	.080	.033-.128
	T+S-	.134	.085-.182	.072	.017-.127	.117	.059-.176	.109	.075-.142
	T-S+	.135	.079-.191	.177	.105-.249	.112	.071-.153	.093	.054-.131
	T-S-	.152	.072-.233	.204	.093-.314	.099	.035-.163	.104	.066-.142
Oulu	All	.131	.089-.173	.106	.058-.154	.145	.096-.195	.169	.107-.230
	T+S+	-	-	-	-	-	-	-	-
	T+S-	.104	.003-.205	-	-	.200	.069-.332	-	-
	T-S+	.167	.050-.284	.085	.001-.169	-	-	-	-
	T-S-	-	-	-	-	.148	.006-.290	-	-

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch away daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Table 11

Women: Daily mean of suicide mortality, and switching away from daylight saving time in fall.

Location	Days	1969-80 *				1995-2003 (DST2)
		-1 m		+1 m		-1 m		+1 m
		m	CI	m	CI	m	CI	m	CI
Finland	All	.029	.026-.032	.025	.022-.029	.032	.026-.038	.027	.022-.032
Helsinki	All	.044	.029-.058	.042	.033-.051	.054	.039-.070	.035	.026-.044
	T+S+	.032	.011-.052	.058	.019-.097	.104	.050-.159	.053	.002-.104
	T+S-	.055	.027-.083	.074	.036-.112	.049	.015-.083	-	-
	T-S+	.046	.015-.076	.032	.010-.054	.034	.002-.067	.040	.016-.065
	T-S-	.026	.001-.051	-	-	.064	.030-.099	-	-
Oulu	All	.038	.005-.072	.032	.010-.054	.027	.004-.051	.051	.012-.090
	T+S+	-	-	-	-	-	-	-	-
	T+S-	-	-	-	-	-	-	-	-
	T-S+	-	-	-	-	-	-	-	-
	T-S-	-	-	-	-	-	-	-	-

Daily mean of suicide mortality during one month period before (-1 m), and after (+1 m) the switch away daylight saving time.

* = DST was not in use in Finland

m = daily mean of suicide mortality

CI = confidence interval of the mean

Relationship between daylength and suicide in Finland

Figures & Tables

Table 1

Table 2

Figure 1

Table 3

Table 4

Table 5

Table 6

Table 7

Table 8

Table 9

Table 10

Table 11

Paradigm

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