Association of working hour characteristics and on-call work with risk of short sickness absence among hospital physicians: A longitudinal cohort study

Figures & data

Table 1. Descriptions of working hour characteristics evaluated in this study

Working hour dimension/variable	Description
Length of working hours
Weekly working hours (h)	The average weekly (from Monday 00:00 to Sunday 24:00) working hours in the case or control window
Shift length (h)	The average length of all shifts in the case or control window
Number of normal (≤12 h) shifts	Number of ≤12 h shifts in the case or control window
Number of long (>12 h) shifts	Number of > 12 h (and ≤24 h) shifts in the case or control window
Number of very long (> 24 hours) shifts	Number of >24 h shifts in the case or control window
Categorized long and very long shifts	The number of long and very long shifts was categorized for thresholds of 0, 1–2, 3–4, and ≥5 long or very long shifts within 4 weeks based on the distribution of these working hour characteristics
Length of duty period (h)	The average length of duty periods (i.e. consequent shifts without any rest between) in the case or control window
Shift intensity
Number of consecutive working days	The average number of consecutive work days (without free days) in the case or control window (starting from and ending to a free day or other absence from work)
Categorized consecutive working days*	The number of consecutive working days was categorized for thresholds of 3–5, 2 or 6, 7, and 1 or ≥8 consecutive working days based on the FIOH recommendations (Finnish Institute of Occupational Health 2021) in the case or control window
Number of work shifts in a day	The average number of consecutive work shifts in a day (i.e. within a date) in the case or control window
Number of on-call shifts	The average number of on-call shifts in the case or control window
Categorized on-call shifts	The number of on call shifts was categorized for thresholds of 0, 1–2, 3–4, and ≥5 on-call shifts in the case or control window based on the collective bargaining agreement of physicians in Finland
Number of short (<11 h) shift intervals	Number of shift intervals of <11 h in the case or control window
Categorized short shift intervals	The number of short shift intervals was categorized for thresholds of 0–1, 2–4, 5–11 and ≥12 short shift intervals in the case or control window based on the FIOH recommendations (Finnish Institute of Occupational Health 2021)

*In the categorization of consecutive working days, based on previous research, we assumed that very few (1 or 2) or very many (6, 7, 8 or more) consecutive working would be more strenuous than 3–5 days. The category 3–5 consecutive working days was used as reference, as 3–5 work days mainly resemble regular working hours in day work.

Table 2. Descriptive statistics (mean, standard deviation [SD]) and frequencies (with proportion, %) of working hour characteristics and on-call shifts in the case and control windows of 28 days

Working hour characteristics	Physicians, n = 2845
	Case window		Control window
	mean	SD	mean	SD
Length of working hours
Weekly working hours (h)	20.9	2.1	20.5	8.6
Shift length (h)	8.7	1.5	8.7	1.6
Number of normal (≤12 h) shifts	14.8	4.8	14.0	5.2
Number of long (>12 h) shifts	1.5	1.9	1.5	2.2
Number of very long (>24 hours) shifts	0.7	1.1	0.6	1.1
Length of duty period (h)	9.7	2.0	9.8	2.2
Shift intensity
Number of consecutive working days	4.1	1.4	4.3	1.8
Number of work shifts in a day	1.7	0.5	1.7	0.5
Number of on-call shifts	1.6	1.8	1.6	2.2
Number of short (<11 h) shift intervals	4.0	1.6	3.3	1.5
Thresholds for working hour characteristics^#	n	%	n	%
Number of long (>12 h) shifts^3
0	1140	40	1174	41
1–2	1073	38	1072	38
3–4	443	16	410	14
≥5	189	7	189	7
Number of very long (>24 hours) shifts^3
0	1782	63	1803	63
1–2	820	29	829	29
3–4	206	7	188	7
≥5	37	1	25	1
Shift intensity
Number of consecutive working days^1
3–5	2264	80	2178	78
2 or 6	387	14	385	14
7	51	2	68	2
1 or ≥8	114	4	149	5
Number of work shifts in a day^3
1	957	34	959	34
2	1814	64	1779	64
3	48	2	42	2
4*	1	0	0	0
Number of on-call shifts^2
0	1003	35	1055	37
1–2	1109	39	1135	40
3–4	571	20	494	17
≥5	162	6	161	6
Number of short shift intervals (4 weeks)^1
0–1	148	5	339	12
2–4	1672	59	2089	73
5–11	1023	36	417	15
≥12*	2	0	0	0

^#Where available, we have utilized the traffic light recommendations of FIOH¹ for thresholds of working hour characteristics and, for on-call shifts, we based the categorization on collective bargaining agreement of physicians² or on distribution³

* For statistical analyses, this category was collapsed with preceding category

Table 3. Conditional logistic regression (odds ratio, OR, with 95% confidence intervals, CI) for the associations between working hour characteristics and on-call shifts in the 28 days case and control windows and first incident sickness absence of physicians

	Crude model		Adjusted model*
	OR	95% CI	OR	95% CI
Length of working hours
Weekly working hours (h)	1.01	1.00, 1.02	-	-
Shift length (h)	0.97	0.94, 1.01	1.09	1.04, 1.15
Number of normal (≤12 h) shifts	1.06	1.04, 1.08	-	-
Number of long (>12 h) shifts
0	1		1
1–2	1.09	0.83, 1.44	1.26	1.00, 1.57
3–4	1.21	0.90, 1.63	1.78	1.47, 2.15
≥5	1.12	0.71, 1.77	2.54	1.68, 3.84
Number of very long (>24 hours) shifts
0	1		1
1–2	1.05	0.96, 1.15	1.14	1.03, 1.26
3–4	1.23	1.04, 1.46	1.51	1.30, 1.75
≥5	1.70	1.13, 2.56	2.62	1.61, 4.27
Length of duty period (h)	0.97	0.93, 1.00	1.18	1.09, 1.27
Shift intensity
Number of consecutive working days
3–5	1		1
2 or 6	0.97	0.84, 1.11	1.09	0.92, 1.30
7	0.62	0.37, 1.02	0.64	0.39, 1.03
1 or ≥8	0.66	0.54, 0.81	0.93	0.71, 1.21
Number of work shifts in a day
1	1		1
2	1.09	0.92, 1.29	1.25	1.08, 1.45
3	1.52	1.10, 2.10	1.72	1.17, 2.53
Number of on-call shifts
0	1		1
1–2	1.12	1.05, 1.20	1.23	1.15, 1.32
3–4	1.36	1.04, 1.79	1.74	1.35, 2.24
≥5	1.22	0.89, 1.65	2.15	1.44, 3.21
Number of short (<11 h) shift intervals
0–1	1		1
2–4	2.47	1.94, 3.16	2.88	2.25, 3.69
≥5	10.75	0.59, 12.05	12.61	8.88, 17.90

*Adjusted for the weekly working hours and the number of normal (≤12 h) length shifts. Statistically significant OR and 95% CI indicated with boldface.

Table 4. Conditional logistic regression (odds ratio, OR, with 95% confidence intervals, CI) for the associations between working hour characteristics in the 28 days case and control windows and first incident short (1–3 days) sickness absence of physicians with or without on-call shifts

	On-call work (n = 1842)		No on-call work (n = 1003)
	OR*	95%CI	OR*	95%CI
Length of working hours
Shift length (h)	1.06	0.98, 1.15	1.75	1.17, 2.63
Number of long (>12 h) shifts
0	1		1
1–2	1.09	0.73, 1.65	2.82	1.87, 4.27
3–4	1.43	0.96, 2.13	37.72	5.27, 269.68
≥5	1.78	1.12, 2.81	na	-
Number of very long (>24 hours) shifts
0	1		1
1–2	1.18	1.01, 1.38	3.81	2.06, 7.05
3–4	1.51	1.34, 1.71	42.87	2.59, 697.54
≥5	2.50	1.21, 5.16	na	-
Length of duty period (h)	1.17	0.98, 1.40	2.95	1.94, 4.50
Shift intensity
Number of consecutive working days
3–5	1		1
2 or 6	0.99	0.83, 1.18	0.93	0.69, 1.24
7	0.49	0.21, 1.13	0.92	0.33, 2.60
1 or ≥8	0.95	0.70, 1.28	0.90	0.59, 1.37
Number of work shifts in a day
1	1		1
2	1.22	0.89, 1.66	3.08	2.43, 3.91
3	1.69	1.08, 2.64	na	-
Number of short (<11 h) shift intervals
0–1	1		1
2–4	2.76	1.98, 3.85	2.43	0.93, 6.30
≥5	9.09	6.00, 13.76	17.04	5.58, 51.99

Adjusted for the weekly working hours and the number of normal (≤12 h) length shifts. Statistically significant OR and 95% CI indicated with boldface.

na = not assessed due to a low number of observations in the category

Finnish Institute of Occupational Health. 2021. Työaikojen kuormittavuuden arviointi jaksotyössä (in English: Evaluation of working hour loading in irregular shift work). Helsinki.

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