The impact of insomnia on anxiety and depression: a longitudinal study of non-clinical young Chinese adult males

Sample size calculation

G*Power software version 3.1.9.2 was used to estimate required sample size of this study. The present study used hierarchical regression analysis to analyze interactions between insomnia, anxiety, and depression. Therefore, F-test (Linear multiple regression: Fixed model, R2 deviation from zero) was chosen and effect size (f2) was set at 0.15 [20,21,22], alpha value was set at 0.05. Approximately 68 participants would provide 80% power and 88 participants would provide 90% power to detect a statistical significance.

Subjects and procedures

There were 2 inclusion criteria in this study. They were listed as follow: (1) no dyslexia, (2) Chinese male, and (3) aged 18 years old or above. The exclusion criterion was the experiences of being diagnosed with mental disorder. Convenient sampling method was applied to recruit subjects in Shanghai.

The respondents were asked to sit in a room and filled out all the paper questionnaires. All participants signed written informed consent form in ethics approval and consent to participate form. The study was approved by the ethical committee of Naval Medical University in accordance with the ethical standards established in the 1964 Declaration of Helsinki and its later amendments. Participants received gifts after completing the survey. All the subjects were assured their responses were anonymous and confidential and they were free to withdraw at any time without penalty.

A flow diagram of sample selection is presented in Fig. 1. 288 participants were recruited in non-clinical young Chinese male population in the first investigation (Time point 1, T1) with a response rate of 98.61% (284 valid questionnaires were received following the exclusion criteria). 120 of them participated in the second survey (Time point 2, T2) with a response rate of 100%. 168 participants didn’t complete the study due to house moving, out of communication, business trip and so on. Therefore, data of 120 subjects from 2 survey was analyzed. Participants were asked to respond to a questionnaire consisting of established instruments that assessed insomnia, anxiety, and depression in October 2017 (T1) and accepted a re-test 8 months later in June 2018 (T2). The average age of 120 subjects was 24.30 ± 4.47, and the average year of educational level was 14.03 ± 1.79.

Fig. 1figure 1

Flow Diagram of Sample Selection

MeasurementDemographics

In the present study, demographic information including name, age, and educational level were recorded.

Athens insomnia scale, AIS

AIS was developed by Soldatos and colleagues to assess the severity of insomnia (including sleep induction, awakenings during the night, early morning awakening, total sleep time, overall quality of sleep, problems with sense of well-being, functioning, and sleepiness during the day) according to ICD-10 diagnostic criteria. It is a self-assessment psychometric tool in reliably establishing the diagnosis of insomnia which has previously shown high consistency, reliability, and external validity [23, 24]. AIS includes 8 items, and each item can be rated 0–3, with 0 corresponding to no problem at all and 3 to very serious problem. The responders are requested to rate each item positive only if they had experienced their sleep difficulty at least three times a week during the last month. Total score of AIS ranged from 0 to 24. A total score of 6 or more indicated that the participant illustrated insomnia symptoms. In the present study, the Cronbach’s alpha was 0.821 (T1) and 0.821 (T2).

Generalized anxiety disorder-7, GAD-7

The GAD-7 is a valid and efficient tool for screening GAD and assessing its severity in clinical practice and research [25]. The 7-item questionnaire was applied to ask participants how often they were bothered by each symptom during the last 2 weeks. Response options were “not at all”, “several days”, “more than half the days” and “nearly every day” scored as 0, 1, 2, and 3, respectively. The cut-off score for the diagnosis of anxiety is 10. In the present study, the Cronbach’s alpha was 0.871 (T1) and 0.819 (T2).

Patient health questionnaire-9, PHQ-9

The PHQ-9 includes 9 items pertaining to the DSM-IV criteria for depressive disorder [26]. Each item is rated on a 4-point scale from 0to 3 (0-never; 1- several days; 2-more than half the time; and 3-nearly every day) within the last two weeks before the completion of the survey. The cut-off score for the diagnosis of depression is 10. As long as item 9 appears (thoughts that you would be dead or of hurting yourself in some way), it is considered as positive, regardless of the number and duration of occurrence. In the present study, the Cronbach’s alpha was 0.784(T1) and 0.826(T2).

Data analysis

Shapiro-Wilk normality tests were applied to test data distribution. The results shown that the total scores of insomnia, anxiety and depression weren’t normally distributed (Ps < 0.001). Therefore, comparisons of total scores of insomnia, anxiety and depression between the two time points were made using Wilcoxon tests. Pearson correlation tests were used to analyze the correlations between insomnia, anxiety, and depression in T1 and T2, respectively. The cross-lagged analysis using regression analysis was conducted to examine prospective associations among insomnia, anxiety, and depression according to the methods described in previous research [27]. In Fig. 2A, a cross-lagged model was described in which variables A and B are measured at two time points (T1 and T2), resulting in three types of relationships: synchronous correlations (1 and 2), auto correlations (3 and 4), and cross-lagged correlations (5 and 6). The cross-lagged estimates can be interpreted as A1(B1) predicting relative changes in B2(A2). IBM SPSS 21.0 Software was used for the data analyses. P < 0.05, P < 0.01 and P < 0.001 were accepted as statistically significant probability values.

Fig. 2figure 2

Cross-lagged model of insomnia, anxiety, and depression

Note: A- Cross-lagged model; B- Cross-lagged analysis of insomnia and anxiety; C- Cross-lagged analysis of insomnia and depression. *p < 0.05, **p < 0.01, ***p < 0.001

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