Insomnia symptoms mediate the association between eveningness and suicidal ideation, defeat, entrapment, and psychological distress in students

Figures & data

Table 1. Bivariate associations (Kendall’s τ_b with 95% confidence intervals in parentheses) and descriptive statistics. Mdn = median, IQR = interquartile range, M = mean, S = standard deviation

		1.	2.	3.	4.	5.	6.	7.	8.	9.	Mdn (IQR)	M (S)
1.	Age										21 (19–23)	20.7 (2.04)
2.	Insomnia	.03 (−.11, .17)									13 (7–19)	13.2 (7.62)
3.	Chronotype	.06 (−.08, .20)	−.24 (−.37, −.10)								13 (10–16)	13.4 (3.90)
4.	DASS-21	−.06 (−.20, .08)	.44 (.33, .55)	−.22 (−.35, −0.08)							34 (16–58)	40.1 (22.7)
5.	Depression	−.10 (−.24, .04)	.40 (.27, .51)	−.22 (−.36, −.08)	.73 (.66, .79)						10 (4–20)	12.9 (11.3)
6.	Anxiety	−.05 (−.19, .09)	.39 (.26, .51)	−.21 (−.34, −.07)	.70 (.62, .76)	.48 (.36, .58)					8 (2–18)	11.4 (9.94)
7.	Stress	.02 (−.12, .16)	.41 (.28, 52)	−.17 (−.31, −.03)	.76 (.69, .82)	.52 (.41, .62)	.58 (.47, .66)				14 (8–22)	15.8 (10.0)
8.	Defeat	−.09 (−.23, .05)	.39 (.26, .51)	−.20 (−.34, −.06)	.57 (.47, .66)	.65 (.55, .72)	.42 (.30, .53)	.44 (.32, .55)			19.5 (12–30.75)	22.8 (13.8)
9.	Entrapment	−.05 (−.19, .10)	.36 (.23, .48)	−.26 (−.39, −.13)	.61 (.51, .69)	.66 (.57, .74)	.45 (.33, .56)	.48 (.36, .58)	.65 (.56, .72)		14.5 (5–26)	18.0 (15.6)
10.	Suicidal Ideation	−.02 (−.16, .12)	.34 (.21, .46)	−.14 (−.28, .00)	.48 (.36, .48)	.50 (.38, .60)	.39 (.26, .50)	.39 (.26, .50)	.51 (.40, .61)	.52 (.41, .62)	3 (0–13)	8.82 (11.6)

Table 2. Two-tailed Mann–Whitney U-test statistics for M-types v. E-types. Mdn = median, IQR = interquartile range, U = Mann–Whitney U-test statistic, r = effect size (|Z|/√N; Field et al. 2012, 665). Significance levels of between-group differences: * p < .05, ** p < .01, *** p < .001. Holm-Bonferroni corrected for 30 tests (3 pairings of chronotype, with 10 variables each) significance levels: † p < .05, †† p < .01, NS not significant. If no daggers, then no change to significance level following correction. No significant difference in age between groups

	M-types (N = 34)		E-types (N = 60)
	Mdn	IQR	Mdn	IQR	U	r
Age	20	20–23	21	18–22	959.5	.05
Insomnia^***††	11	5–15.5	19	12.5–22	1492.5	.38
Chronotype***	19	18–20	9	8–10	0	.83
DASS-21^**†	21	14–52	53	28–82.5	1430.5	.33
Depression^**†	5	2–12	16	7.5–28	1407.5	.31
Anxiety^**†	6	2–15.5	16	7.5–24.5	1403.5	.31
Stress^**NS	12	8–18	18	12–32	1358.5	.27
Defeat^**NS	18	10.25–26.75	28	15–42.5	1388	.30
Entrapment^***††	7.5	1.25–2375	21.5	12.5–40.25	1508	.40
Suicidal Ideation^*NS	2.5	0–14.25	7.5	2–23.5	1271	.20

Table 3. Two-tailed Mann–Whitney U-test statistics for N-types v. E-types. Mdn = median, IQR = interquartile range, U = Mann–Whitney U-test statistic, r = effect size (|Z|/√N; Field et al. 2012, 665). Significance levels of between-group differences: * p < .05, ** p < .01, *** p < .001. Holm-Bonferroni corrected for 30 tests (3 pairings of chronotype, with 10 variables each) significance levels: † p < .05, †† p < .01, NS not significant. If no daggers, then no change to the significance level following correction. No significant difference in age between groups

	N-types (N = 96)		E-types (N = 60)
	Mdn	IQR	Mdn	IQR	U	r
Age	20.5	19–23	21	18–22	2804	.02
Insomnia***	10.5	5–16	19	12.5–22	4293	.41
Chronotype***	14	13–15.25	9	8–10	0	.84
DASS-21^***††	28	15.5–52.5	53	28–82.5	3947.5	.31
Depression^***††	8	2–18	16	7.5–28	3834.5	.28
Anxiety^***††	7	2–14	16	7.5–24.5	3916.5	.30
Stress^**†	13	7.5–20	18	12–32	3717	.24
Defeat^***††	16.5	11–27.25	28	15–42.5	3957	.31
Entrapment***	12	5–20	21.5	12.5–40.25	4073	.35
Suicidal Ideation^***††	2	0–9	7.5	2–23.5	3959.5	.32

Table 4. Bootstrapped point estimates and 95% bias-corrected confidence intervals (in parentheses) for direct and indirect effects as represented in Figure 1. Point estimates and 95% confidence intervals of indirect and direct pathways resulting from multiple serial mediation analysis. Generated using 50000 bootstrapping iterations. Italics indicate insignificant relations (i.e. where confidence intervals include zero). P_m = proportion mediated as a percentage of total effect size using point estimates = a × b/(c’ + a × b). Ratio = ratio of scale-normalized change in outcome variable to scale-normalized change in chronotype (e.g. a ratio value of −0.39 means that a 10% increase in chronotype score is associated with a 3.9% decrease in outcome score)

Outcome	a	b	a × b	c’	a × b + c’	Pm (%)	Ratio
DASS-21	−0.62 (−0.90, −0.33)	2.13 (1.74, 2.49)	−1.32 (−1.98, −0.72)	−1.03 (−1.86, −0.21)	−2.34 (−3.41, −1.30)	56.2	−0.39
Depression	−0.62 (−0.90, −0.33)	0.73 (0.55, 0.90)	−0.45 (−0.71, −0.24)	−0.50 (−0.86, −0.13)	−0.95 (−1.36, −.52)	47.4	−0.47
Anxiety	−0.62 (−0.90, −0.33)	0.66 (0.51, 0.82)	−0.41 (−0.63, −0.23)	−0.37 (−0.69, −0.06)	−0.78 (−1.16, −0.41)	52.6	−0.39
Stress	−0.62 (−0.90, −0.33)	0.74 (0.58, 0.89)	−0.46 (−0.70, −0.25)	−0.16 (−0.47, 0.15)	−0.46 (−0.70, −0.25)	74.6	−0.31
Defeat	−0.62 (−0.90, −0.33)	1.00 (0.81, 1.18)	−0.62 (−0.97, −0.33)	−0.48 (−0.91, −0.05)	−1.10 (−1.64, −0.57)	56.3	−0.36
Entrapment	−0.62 (−0.90, −0.33)	0.90 (0.66, 1.11)	−0.56 (−0.89, −0.30)	−0.98 (−1.52, −0.46)	−1.54 (−2.15, −0.93)	36.3	−0.50
Suicidal Ideation	−0.62 (−0.90, −0.33)	0.75 (0.54, 0.96)	−0.47 (−0.76, −0.24)	−0.10 (−0.51, 0.30)	−0.57 (−1.04, −0.09)	82.05	−0.24

Figure 1. Mediation model for chronotype and outcomes via insomnia

Field AP, Miles J, Field Z. 2012. Discovering statistics using R. London: Sage.

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