2. Materials and methods
An observational, cross-sectional, descriptive, and multicentre study was conducted during 2013 in 126 nursing homes in different Spanish cities. The nursing homes were selected randomly to representative each region of Spain. The Granmo 7.0 program was used to calculate a representative sample, which resulted in a minimum of 87 nursing homes and 450 nurses (equivalent to RN in Spain). Inclusion criteria of the nursing homes were as homogeneous as possible. Nursing homes should be private institutions with at least 2 staff nurses. The sociodemographic and labor variables included age, sex, family responsibilities, number of elderly dependents, shift, and work area. The Ethics Committee of the Cantabrian Health Service approved the study. Consent, which was obtained in order to conduct the study, was granted by the ethics committee of all nursing homes.