Study area and subjects
This cross-sectional study was performed in Northeastern China from May to September 2017. First, according to the information of pension institutions on the website of the Civil Affairs Bureau, the institutions with more than 500 beds were selected.Liaoning is a province with 14 prefecture-level cities, however not too many pension institutions are qualified for this research. And mostly are located within and near the provincial capital. With the support for project funding, we selected eligible institutions from Shenyang, Anshang, Tieling and Benxi and trained the personnel accordingly. In consideration of the economic status, cultural background and cooperation level, we selected six pension institutions from these cities. Two in Shenyang, two in Anshan, one in Tieling, and one in Benxi. The inclusion criteria of the study population were: age≥60; stay time≥6 months; not diagnosed with Alzheimer's disease; voluntary participation in the study. Exclusion criteria of the study population: Elderly with acute diseases during the investigation.We primarily double confirm with elder people’s family if elders have been diagnosed as Alzheimer as there was limited resources for us to look through.Besides, all the participants were interviewed by using a questionnaire exploring cognitive function, demographic characteristics, and influencing factors. The questionnaire also made based on the Pittsburgh Sleep Quality Index (PSQI) and Geriatric Depression Scale (GDS). The selection of sample size is 5-10 times of the number of items of all scales. The sample size needs to consider 10-20% error . There were 52 items in this study. Therefore, the sample size should be 286 ~ 624. The sample size was proportionally determined based on each facility’s bed quantities. And participants were selected randomly. The specific sampling results is shown in Table 1. Considering the economic and human factors, the final sample size were 588. We contacted a total of 588 elderly people, of whom 553 were interviewed and completed questionnaires. After screening for the cognitive function using the Mini-Mental State Examination (MMSE) . The MMSE has been widely used to screen for cognitive defects among the elderly10. The total score of the MMSE ranges from 0 to 30. Combined with the educational level of the elderly, the diagnostic criteria for cognitive impairment among the elderly are as follows: illiteracy is ≤17 points, primary school is ≤20 points, secondary school (including technical secondary school) is ≤22 points, and university is ≤23 points. 507 elderly adults without cognitive defects were chosen as participants.
Ethics approval and consent to participate
All participants were asked to fulfill a consent form prior participating the study. Each participants was well noted that they have the right to decline or withdraw from the survey at any time. Project detail has been introduced in detail with contact persons from each institution. And the project has been conducted with the permission from China Medical University(Address of: No.77, Puhe Road, Shenyang North New Area, Shenyang 110122, China)under the protocol and consent approved by the Ethics Review Committee of China Medical University.(Ethical Review Code: AF-SOP-07-1.1-01).
Geriatric Depression Scale (GDS)
The GDS  is a 30-item self-report assessment used to identify depression among the elderly. In the GDS, 20 questions are answered “yes” (scored 1) or “no” (scored 0), while the remain 10 questions are evaluated the opposite way (where “yes” is scored 0 and “no” is scored 1). The total score of the GDS ranges from 0 to 30, with a score of ≥11 indicating depression.
Pittsburgh Sleep Quality Index (PSQI)
The PSQI  is a self-report questionnaire that assesses sleep quality over a one-month time interval. The measure scale consists of seven components, including subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbance, use of sleeping medication, and daytime dysfunction. The score for each component ranges from 0 to 3, where 0 indicates “no difficulty” and 3 indicates “very difficult.” The total score of the PSQI ranges from 0 to 21, with a score of >7 denoting poor sleep quality or having a sleep disorder.
Both scales are already used in China with citation. We also used a self-designed questionnaire for baseline information including age, sex, marital status, pension, economic status, chronic disease, self-care, body aches, chewing ability, ability to go out alone, exercise frequency, regular diet, smoking, filial piety, and loneliness. The researchers used self-assessment questionnaire to evaluate whether the participants were lonely or lack of family car.
We recruited 35 investigators to support the project and standardized training were provided for them in order to conduct questionnaire on their own. In consideration of the facts that some elderly people were already unable to read, we apply face-to-face interviews. During the interview, the investigator could inform the elder regarding the questionnaire in detail but could not be subjective nor changing the contents randomly. For certain cases, contents could be explained in more details on the condition that not affecting the survey result. Investigators observed participants’cognitive function to ensure the survey result accuracy.
Items for which over 95% of participants had the same answers were excluded from the data analysis; these items included race (“Han” accounted for 96.8%) and medical insurance (“Have” accounted for 98.9%).
In addition, the proportion of missing items was <5% among elderly adults with poor or good sleep quality. No missing items were processed. We performed a statistical analysis of the data using SPSS Statistics 20.0. We conducted a univariate analysis using the chi-square test, and a multivariate analysis using binary unconditional logistic regression analysis. A P value less than 0.05 was considered statistically significant. In this study, the elderly people with good sleep quality and poor sleep quality were investigated. The elderly depression in pension institutions was taken as the dependent variable, and the content in the general data was used as the independent variable.