Purpose: Weak empirical evidence exists showing that nursing home staffing levels influence quality of care. We propose that weak findings have resulted in many prior analyses because research models have underspecified the labor composition needed to influence care processes that, in turn, influence quality of care. In this analysis, we specified the nursing home labor composition by using staff stability, use of agency staff, and professional staff mix, in addition to staffing levels. Design and Methods: Data used in this investigation came from surveys of nursing home administrators (N = 6,005); Nursing Home Compare; the Online Survey, Certification and Reporting data; and the Area Resource File. Staffing characteristics, quality indicators, facility, and market information from these data sources were all measured in 2004. Results: The regression analyses showed that staffing levels alone were weakly associated with the six quality measures examined. However, when the regression models were more fully specified (by including agency staff, stability, and professional staff mix), staffing levels were generally associated with the quality measures (i.e., 15 of the 18 staffing coefficients were significant). Implications: Simply adding more staff may be a necessary but not sufficient means of improving nursing home quality. Some accounting for agency staff, stability, and professional staff mix is also needed.