The purpose of this study was to identify factors related to nurses' organizational citizenship behavior using multilevel analysis which included both nurse characteristics at individual levels and nursing unit characteristics at group levels.

The sample was composed of 1,996 nurses who were selected from 182 nursing units in 28 hospitals in six metropolitan cities and seven provinces using cluster sampling. Data were collected using self-reported questionnaires from February to March 2006.

The results of the study indicated that individual level variables related to organizational citizenship behavior were religion, job position, clinical career, self efficacy, positive affectivity, and supervisor support. The group level variables related to organizational citizenship behavior were collective efficacy, number of nurses in a nursing unit, and the average salary level of a nursing unit. 30.9% of individual level variances of organizational citizenship behavior were explained by the nurses' individual level variables. The explanatory power of group level variables, which is related to group level variances of organizational citizenship behavior, was 75.5%.

This research showed that it was necessary to develop appropriate strategies related to not only individual factors, but also higher-level organizational factors such as collective efficacy, to improve individual performances in the hospital.