Demographic characteristics of the participants were described using frequency and percentage for categorical data and mean and standard deviation for continuous data. The rate was calculated using the number of nurses who reported WPV with or without JA, at least one occasion during the past 12 months as the numerator and the total number of nurses who responded to the questionnaire as the denominator. The 95% confidence interval (CI) of the rate was computed based on normal approximation to binomial distribution. Probability sampling weight was used to account for the sampling design of the study. This method was also used to calculate the rate of WPV with JA. To investigate factors that affect WPV, odds ratios (ORs) and their 95% confidence intervals (95%CIs) were estimated using multiple logistic regression for survey sampling. This analysis was adjusted for baseline variables that were considered biologically and sociologically relevant or which showing a univariate relationship with outcomes such as age, gender, job characteristics (e.g. non-service nurses, worked at nighttime, workload), previous and current illnesses such as musculoskeletal disorder (MSD), neurological illnesses, cardiovascular diseases, etc. All analyses were performed using Stata version 11.0 (StataCorp, College Station, TX). All test statistics were two-sided and a p-value of less than 0.05 was considered statistical significant. This project was approved by the Human Research and Ethics Committees of the Ministry of Public Health of Thailand.