An Exploration of Self-Reported Sleep Inertia Symptoms Using Network Analysis

Figures & data

Table 1 Demographic Characteristics of the Current Sample (N=1240)

Variables	n	%
Sex
Male	565	45.6
Female	675	54.4
Age, years
≤18	200	16.1
19–20	653	52.7
21–22	248	20.0
≥23	139	11.2
Grade
Freshman	602	48.5
Sophomore	290	23.4
Junior and above	348	28.1
Sleep latency, minute
≤15	730	58.9
16~30	406	32.7
≥31	104	8.4
Sleep duration, hours
<6	387	31.2
6~7	552	44.5
>7	301	24.3
	Mean	SD
Duration of sleep inertia, minute	11.7	13.72
Times, days/week	2.8	2.16
SIQ total score	56.0	18.79

Abbreviations: SD, standard deviation; SIQ, Sleep Inertia Questionnaire.

Table 2 Mean, Standard Deviation, Skewness, and Kurtosis for the SIQ Items (N=1240)

Construct/Nodes	Label	Mean (SD)	Skewness	Kurtosis	Predictability
Difficulty getting up	SIQ_1	3.02(1.26)	−0.05	−1.23	50%
Need an alarm to wake up	SIQ_2	3.31(1.38)	−0.41	−1.15	39%
Hit the snooze button on the alarm	SIQ_3	2.79(1.43)	0.12	−1.40	41%
Bump into and drop things	SIQ_4	1.8(1.05)	1.25	0.77	35%
Move more slowly	SIQ_5	2.93(1.26)	−0.14	−1.20	59%
Feel sleepy	SIQ_6	3.24(1.25)	−0.42	−0.96	67%
Heavy, sore, or itchy eyes	SIQ_7	2.87(1.31)	0.01	−1.23	64%
Tired or heavy arms and/or legs	SIQ_8	2.84(1.27)	0.03	−1.18	70%
Groggy, fuzzy or hazy mind	SIQ_9	2.77(1.27)	0.12	−1.18	70%
Get winded more easily	SIQ_10	1.99(1.08)	1.06	0.38	60%
Difficulty keeping balance	SIQ_11	2.22(1.2)	0.74	−0.52	65%
Feel tense	SIQ_12	2.05(1.09)	0.92	0.08	–
Anxious about the upcoming day	SIQ_13	2.27(1.18)	0.65	−0.57	71%
Dread starting your day	SIQ_14	2(1.09)	0.99	0.23	73%
Wish to sleep more	SIQ_15	3.69(1.25)	−0.85	−0.33	52%
Difficulty concentrating	SIQ_16	2.68(1.26)	0.18	−1.11	67%
Think more slowly	SIQ_17	2.85(1.27)	−0.04	−1.21	–
React more slowly	SIQ_18	2.81(1.28)	0.00	−1.24	73%
Make more mistakes/errors	SIQ_19	2.6(1.22)	0.24	−1.04	73%
Cannot imagine being able to wake up	SIQ_20	2.77(1.37)	0.16	−1.28	56%
Difficulty getting thoughts together	SIQ_21	2.54(1.24)	0.35	−0.96	71%

Notes: (Missing): Items of SIQ_12 and SIQ_17 were excluded from the subsequent network analysis. Adapted from Kanady JC, Harvey AG. Development and validation of the Sleep Inertia Questionnaire (SIQ) and assessment of sleep inertia in analogue and clinical depression. Cognitive Ther Res. 2015;39(5):601–612. Table 2 is copyright protected and excluded from the open access licence.²⁸

Abbreviations: SD, standard deviation; SIQ, Sleep Inertia Questionnaire.

Figure 1 Network structure of the sleep inertia symptoms in the total sample (N= 1240). Blue lines indicate positive associations, and orange lines indicate negative associations. The thickness of an edge represents the association strength, the size of a circle represents the node strength, and the area of red ring indicates the predictability.

Note: SIQ questionnaires are adapted from Kanady JC, Harvey AG. Development and validation of the Sleep Inertia Questionnaire (SIQ) and assessment of sleep inertia in analogue and clinical depression. Cognitive Ther Res. 2015;39(5):601–612. Table 2 is copyright protected and excluded from the open access licence.²⁸

Figure 2 Centrality indices of network structure of sleep inertia symptoms, shown as standardized values z-scores.

Figure 3 Stability of centrality indices as assessed using the case-dropping bootstrap method. The x-axis represents the percentage of cases of the original sample used at each step. The y-axis represents the average of correlations between the centrality indices from the original network and the centrality indices from the networks that were re-estimated after excluding increasing percentages of cases. Each line indicates the correlations among betweenness, closeness, and strength, while areas indicate 95% CI.

Figure 4 Estimation of node strength difference by bootstrapped difference test. Bootstrapped difference tests between node strength of factors. Gray boxes indicate nodes that do not significantly differ from one-another. Black boxes represent nodes that differ significantly from one another (α = 0.05). White boxes show the values of node strength.

Figure 5 Estimated network models for sleep inertia symptoms between females and males. Left panel: network structure in females (n = 675); right panel: network structure in males (n = 565).

Kanady JC, Harvey AG. Development and validation of the Sleep Inertia Questionnaire (SIQ) and assessment of sleep inertia in analogue and clinical depression. Cognitive Ther Res. 2015;39(5):601–612. doi:10.1007/s10608-015-9686-4

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