Source and study population
This study covers seven regions: north, east, central, south, southwest, northwest, and northeast China. The selection of key industries is based on the representative industries closely related to WMSDs and mentioned in the previous literature, including automobile manufacturing, shoemaking, biopharmaceutical manufacturing, electronic equipment manufacturing, ship and related equipment manufacturing, petrochemical industry, construction, furniture manufacturing, coal mining and washing industry, animal husbandry, medical personnel, automobile 4S shops, vegetable greenhouses, civil aviation crews, and toy manufacturing; a total of 15 industries or working groups. On the one hand, inclusion criteria of the study population were based on workers who are over 18 years old, have worked for more than 1 year, have certain reading and writing abilities, and can understand the meaning of the questionnaire in Chinese. On the other hand, exclusion criteria consisted of people with congenital spinal malformations and patients without WMSDs, such as trauma, infectious diseases, and malignancy. This study has passed the ethical review of the Ethics Review Committee of The Chinese Center for Disease Control and Prevention, and the informed consent was obtained from the participants. Moreover, all methods were performed per relevant guidelines and regulations. Data handling and storage are compatible with this law. All protocols were performed under the Declaration of Helsinki.
Sample size determination and sampling procedures
This study adopted a stratified cluster sampling method to select all on-duty workers meeting the inclusion criteria from representative enterprises in key industries in north, east, central, south, southwest, northwest, and northeast China. A total of 64,052 people were surveyed and 61,034 questionnaires were received, with a response rate of 94.6% (95% CI: 0.951, 0.955); a total of 57,501 valid questionnaires were collected, with an effective rate of 94.2% (95% CI: 0.940, 0.944).
Data collection tool and procedure
The incidence of WMSDs among occupational groups in key industries in different regions of China was investigated using the ergonomic evaluation and analysis system developed by the National Institute for Occupational Health and Poison Control, Chinese Center for Disease Control and Prevention. The system includes four functions: electronic remote operation site ergonomics survey and evaluation tool, real-time data monitoring system, data transmission network, and background data terminal. The survey tool used in this survey is a built-in questionnaire in the system, namely the electronic questionnaire system of the Chinese version of the musculoskeletal disorders questionnaire, which is based on the Nordic Musculoskeletal Disorders Questionnaire (NMQ) [8]. After appropriate modification, it has been proven to have good reliability and validity, and can be used in the Chinese occupational population. The survey contents include ① general information such as age and years of service; ② occurrence of musculoskeletal symptoms; ③ work type, organized form of work, and working posture.
The survey was conducted in 1 an N. One investigator conducted a face-to-face survey with N respondents. The respondents scanned the QR code of the electronic questionnaire and answered questions online. After submitting the questionnaires, they were uploaded directly to the cloud database. Figure 1 shows the implementation process of the study.
Criteria for LBP
The NIOSH criteria for musculoskeletal injury [9] were adopted: pain, stiffness, burning, numbness or tingling, and other uncomfortable symptoms, which were consistent with ①discomfort in the past year; ② discomfort after accepting the current job; ③ no previous accidents or sudden injuries (local effects and discomfort); ④ if discomfort occurred every month or lasted for more than 1 week, it was judged as a musculoskeletal disease in this part.
Data quality control
Quality control is conducted throughout the entire research process, including design, implementation, data collection, and data collation, to ensure the scientific nature of the research conclusions and the authenticity, validity, and reliability of the data.
I Research design
Referring to the relevant literature, clarifying the research purpose, investigation methods, and other vital aspects, and taking appropriate measures to control the possible bias in research design.
II On-site investigation and measurement
Before the investigation, the investigators were strictly trained to fully understand the purpose and significance of the research and master the investigation and monitoring methods. During the survey, the investigators explained the purpose, significance, and requirements and conducted a face-to-face survey. The participants filled in the questionnaire and submitted it on the spot to ensure the authenticity, integrity, and high retrieval rate of information sources.
III Data collection
Investigators monitored the completion of the questionnaires to ensure that all surveyed information was from the participants themselves. The electronic questionnaire had a logical error correction to avoid unreasonable information. If there were blank items, the questionnaire could not be submitted. Thus, the investigator assisted the participants to fill in the blanks to ensure that the information is complete.
Data management and analysis
After the survey data were exported from the backend database, they were statistically processed using SPSS 20.0 statistical software. The measurement data adopted \(\overline{\mathrm{X}}\pm \mathrm{s}\) indicators, and the single factor analysis of WMSDs adopts the χ 2 test method, multivariate analysis was performed using an unconditional logistic regression model.