This study examined associations between low nurse/patient ratios and adverse patient outcomes. In January 2004, a California law went into effect that regulates minimum nurse/patient ratios in hospitals because several studies had documented worse patient outcomes when nurse/patient ratios fell. The estimated costs of complying with this law are at least $400 million/year.
The authors focused on outcomes from patients admitted on Thursdays at a single hospital between 1996–2000 because hospital admissions tend to be the most variable and staff numbers lower on weekends. Admission shocks over the next two days were recorded, and follow-up information was drawn from restricted-use hospital discharge data kept by the state of California. Previous multihospital studies correlating staff ratios and outcomes may be flawed by failing to account for other hard-to-measure characteristics (newer technology, better surgeons, etc., in hospitals with high nurse/patient ratios) that also affect patient outcomes. Also, studies that use within-hospital admission variation between weekend and weekday do not account for the fact that scheduled weekday admissions tend to be less severe than weekend unscheduled admissions. Thus, this study seeks to correct for these conditions by using patients admitted on a weekday, but staying through the weekend when admission shocks occur.
Data analysis focused on three outcomes: in-hospital and seven- and 14-day mortality; relatively longer hospital stays, which were assumed to indicate worse care, rather than a practice of simply discharging unrecovered patients; and hospital readmission. Results found limited evidence that routine (i.e., not caused by a sudden pandemic or other catastrophic event) fluctuations in caseload adversely affected patients. In-hospital and seven- and 14-day mortality did not increase in statistically significant amounts; and readmission rates and lengths of stay were affected modestly, depending on the model used, but still impacts were small.
This study suggests two possible interpretations: that hospitals are able to deal effectively with unexpected fluctuations in patient admission, and/or that these fluctuations have, at most, modest effects on patient outcomes. Both interpretations imply that California's nurse-staffing law will have minor measurable benefits on outcomes considered in this study, while being expensive to implement.