A real-time survey on the psychological impact of mild lockdown for COVID-19 in the Japanese population

To deter the spread of the coronavirus disease 2019 (COVID-19), many countries have imposed a lockdown with restrictions. On 7 April 2020, the Japanese government declared a state of emergency over the COVID-19 outbreak. Japan was in “mild lockdown” which was not enforceable and non-punitive with the declaration. We conducted an online survey to investigate factors associated with psychological distress in the “mild lockdown” under a declared state of emergency for COVID-19. We collected data on 11,333 inhabitants (52.4% women, 46.3 ± 14.6 years) living in the seven prefectures where the declaration was first applied. The investigation dates of this study, 11 and 12 May 2020, were in the final phase of the state of emergency. The survey was conducted in real-time to minimize participants’ recall bias. In addition to psychological inventories often used worldwide, the questionnaires used in this survey included lifestyle and stress management items related to COVID-19 and various socio-demographic items including occupation (e.g. healthcare worker) or income.

urgent need to investigate the association between lifestyle changes related to mild lockdown, psychological status, and socio-demographic profile in the mild lockdown that affects people's lives despite its non-punitive nature. In particular, there is inadequate investigation of the stressors and stress coping during the lockdown. Such analysis can contribute to effective provisions of mental health services in a future pandemic.
Thus, to investigate relative factors to psychological distress in mild lockdown we conducted an online survey of inhabitants living in the seven prefectures where the emergency declaration was first applied. We collected data between 11 and 12 May 2020, the period in the final phase of the state of emergency. Methods participants and data collection. A total of 11,333 individuals participated in our study (52.4% women, mean age = 46.3 ± 14.6 years, range = 18-89 years). The survey was conducted online between 11 May and 12 May 2020. The survey was designed to assess the psychological impact of the mild lockdown on participants for approximately one month or from the start of "mild lockdown. " The exclusion criteria were as follows: (a) aged <18 years, (b) high school students, and (c) living outside the seven prefectures. To sensitively detect the impact of the mild lockdown, participants were recruited only in the seven prefectures where the emergency declaration was first applied (Tokyo, Kanagawa, Osaka, Saitama, Chiba, Hyogo, and Fukuoka). These prefectures were assumed to be susceptible to mild lockdown due to their large populations and the large number of cases reported in these areas. The number of people collected in each prefecture was determined according to the ratio of the number of people living in Tokyo (n = 2,783, 24.6%), Kanagawa (n = 1,863, 16.4%), Osaka (n = 1,794; 15.8%), Saitama (n = 1,484; 13.1%), Chiba (n = 1,263; 11.1%), Hyogo (n = 1,119; 9.9%), and Fukuoka (n = 1,027; 9.1%).
Through Macromill.inc. (Tokyo, Japan), approximately 80,000 people were recruited by email, and data were collected on an online platform. Participants completed the online survey on the second day after receiving a link to the online survey. All participants voluntarily responded to the survey anonymously and provided informed consent online before the survey. Participants received a clear explanation of the survey procedure and could interrupt or terminate the survey at any time without explaining the reason.
This study was approved by the Research Ethics Committee at the Graduate School of Social and Industrial Science and Technology, Tokushima University (acceptance number 212), and was performed in accordance with the ethical standards of the 1964 Declaration of Helsinki and its later amendments.
Measurements. Socio-demographic data. Participants' socio-demographic information was collected, including age, sex, employment status, marital status, and annual household income. To compare the impact on the group assumed to be vulnerable to the effects of lockdown in previous studies 2,4,13,14 , information was collected on whether the individual or a family member was a healthcare worker, whether the individual was currently being treated for a mental problem or severe physical disease, and whether the individual had a history of treatment for a mental problem or severe physical disease. Psychological distress. Psychological distress was measured using the Japanese version of the Kessler Psychological Distress Scale-6 (K6) 15 non-specific psychological stress scale, a six-item screening instrument measuring distress over the past 30 days. Each question was rated on a scale of 0 (none of the time) to 4 (all of the time); total scores ranged from 0 to 24. Owing to its brevity and high accuracy, the K6 is considered an ideal scale for screening for mental disorders in population-based health surveys [15][16][17] . In addition, because the duration of symptoms examined by this scale (the past 30 days) corresponds to the period between the start of mild lockdown and the implementation of the survey (approximately 1 month), we assumed that the scale would sensitively reflect the influence of psychological distress caused by the mild lockdown. We adopted a threshold of five points commonly used to screen for mild-to-moderate mood/anxiety disorders 18 . K6 scores ranging from 5 to 12 were defined as mild-to-moderate psychological distress (MMPD). This threshold is the optimal lower threshold cutoff point for screening for moderate psychological distress 18 . MMPD is considered because of the associated risk of progression to more severe disability as well as current distress and disability 19 . A threshold score of 13 is a criterion traditionally used in previous studies 16,20 . A score of ≥13 was defined as serious psychological distress (SPD). Additionally, a score of ≤4 was defined as no or low psychological distress.
We also used the Japanese version of the Patient Health Questionnaire-9 (PHQ-9) 21 to collect basic information on the mental health of participants; the PHQ-9 consists of nine questions. Depressive symptoms during the past four weeks were reported by the participants, with a score of 0 (not at all) to 3 (nearly every day) 22 . We defined a score of ≥10, as recommended by previous studies 21 , as a cutoff point, meaning that a person is more likely to have major depression. The PHQ-9 has been widely used internationally as a screening scale for depression 23 and is highly reliable and valid 21 .
Loneliness and social networks. We measured loneliness since the declaration of the state of emergency on 7 April 2020 using the Japanese version of the UCLA loneliness scale version 3 (UCLA-LS3) 24 . The UCLA-LS3 consists of 10 items, each rated from 1 (never) to 4 (always) 25 . The scores range from 10 to 40, with higher scores indicating higher levels of loneliness. The UCLA-LS3 is highly reliable and valid 24 , and is an internationally used scale for measuring loneliness [26][27][28] .
We also measured social networks since the declaration of the state of emergency using the Japanese version of the abbreviated Lubben Social Network Scale (LSNS-6) 29 . The LSNS-6 consists of three items related to the family network, three items related to the friendship network, and the number of people in the network is calculated using a six-point scale (0 = none to 5 = nine or more) for each item 30 . The total score ranges from 0 to 30 points, with higher scores indicating a larger social network and <12 points indicating social isolation. The LSNS-6 is highly reliable and valid 29 and has been used in many countries [31][32][33] .
Lifestyle, stress management, and stressors related to mild lockdown. With extensive reference to the literature on the COVID-19 pandemic 2,4,6,14,34 , we developed eight lifestyle and stress management items and seven stressors assumed to be associated with mild lockdown (Table 1). Item 7 (Optimism) was included in the eight lifestyle and stress management items because optimism acts to reduce depression after experiencing a stressful event 35 . We asked participants to rate the frequency of implementation and experience of these items from the start of the mild lockdown to the time of the survey on a scale of 1 (not at all) to 7 (extremely).
The above methods are elaborated versions of descriptions provided in our related work (ref. 8 )

Data records
Data records are available in XLSX format from the Open Science Framework (OSF) platform together with files of the questionnaires 36 . The datasets were anonymized to remove any personal information. Abbreviation guides for variable names are also included in each XLSX file. www.nature.com/scientificdata www.nature.com/scientificdata/ technical Validation Characteristics of the data. A strength of this data is to be able to evaluate the effect of mild lockdown in real-time by minimizing recall bias. Moreover, the investigation dates of this study, 11 and 12 May 2020, were also in the final phase of the state of emergency when the effect of changes in life due to mild lockdown may be amplified. Additionally, psychological questionnaires applied to this survey have been often used worldwide in psychological or psychiatric researches. Thus, our data is comparable with the results in other countries with enforceable lockdowns for COVID-19.
Descriptive results. In our dataset, although 1,707 participants (15.1%) did not provide any data regarding annual household income, there were no missing data in other variables.
The socio-demographic characteristics and sex differences using the χ 2 test are shown in Table 2. There were significant sex differences in all socio-demographic variables except two variables: "the presence of health care worker in participants' family" and "current treatment of psychological problems. " The "Unknown" of annual household income in Table 2 includes the missing values (N = 1707).
Online-only Table 1 displays the descriptive results of psycho-social indexes and items specific to mild lockdown and sex differences in these variables using the t-test. Sex differences were significant in these variables except "healthy sleep habits, " one of the items specific to mild lockdown. In total, 4,146 participants (36.6%) had MMPD (K6 score 5-12) and 1,303 (11.5%) had SPD (K6 score ≥13). In previously published data in 2019 concerning K6 in the Japanese population from the Ministry of Health, Labour and Welfare (217,179 households), 26.9% of participants had SPD or MMPD (i.e., K6 score ≥ 5) 37 . Additionally, the estimated prevalence of depression (PHQ-9 score ≥10) was 2,034 (17.9%). In a previous survey of the general Japanese population conducted in 2013 (N = 3753), 7.9% of participants reported a PHQ-9 score of ≥10 38 .  Table 2. Socio-demographic characteristics and sex difference. † Differences between total number and the numbers indicated in this table are the numbers of "No" or "Not married" because there are no missing data regarding these questions. *Significant sex difference found by residual analysis (adjusted residual > 1.96). The size criteria for φ are: 0.100 = small, 0.300 = medium, 0.600 = large. (2020) 7:372 | https://doi.org/10.1038/s41597-020-00714-9 www.nature.com/scientificdata www.nature.com/scientificdata/ Online-only Table 2 displays the Pearson's correlation coefficients between psycho-social indexes and items specific to mild lockdown. There were significant correlations between these variables except between the K6 score and "online interaction with familiar people" or "preventive behaviors of COVID-19" and between the LSNS-6 score and "difficulties owing to the lack of daily necessities. " There were moderate correlations between the K6 score and "frustration" or "COVID-19-related sleeplessness" scores, between the PHQ-9 score and "frustration" score, and between the UCLA-LS3 score and "optimism" score.
Therefore, sex differences in many socio-demographic variables and psychological and lifestyle items in our data were statistically significant. Moreover, psychological distress indices significantly correlated with several items relating to COVID-19. In the hypothesis testing using our dataset or the comparison with other datasets, our results and particularly sex differences in age should be considered.