1. Johnson, Kathie RN, PhD
  2. Chisholm, Arkia RN
  3. Weatherman, Pat RN

Article Content

Ensuring a safe environment for patients is a top concern for healthcare professionals. Most recently, the interest into ways to improve patient safety has raised questions regarding the effect of nurse work schedules on job performance. Literature states that long hours of work pose serious threats to patient safety, as fatigue reduces reaction time, decreases energy, creates inattention to details, and generally contributes to errors.1 Research comprising 393 hospital staff nurses shows that approximately 40% of the 5,317 work shifts these nurses logged as a part of this study exceeded 12 hours. The risks of making an error were significantly increased when they worked more than 12 hours in a day, overtime, or more than 40 hours in a week. Investigators recommend curtailing the routine use of 12-hour shifts and the elimination of overtime. They also recommend additional research with larger samples, inclusion of other variables, and more precise measurements of error.2


Forsyth Medical Center, Winston-Salem, N.C., is an 850-bed hospital that employs more than 2,000 nurses. The majority of the nurses who work at Forsyth on the inpatient units choose to work a 12-hour shift on a 3 days/week schedule. This choice has been a major source of job satisfaction for these nurses. The implication that 12-hour shifts may impact patient safety was a concern to the nursing staff, as they believe these schedules don't result in the same level of fatigue or stress as the research suggests. Therefore, a decision was made to undertake a controlled study of the effects of 8- versus 12-hour shifts on several measures of staff nurse performance.



Two data collection tools were designed for the purpose of this investigation. The first tool was developed to collect information regarding hours of work, and recorded scheduled hours worked, overtime, and extra shifts worked for each study participant. Demographic information, including shift, unit, years of experience, gender, age, and float status, were also collected, as well as data regarding special shift options and advanced registered nurse practitioner temporaries. The second tool was designed for the collection of job performance information for each participant for each shift worked. Four measures to evaluate nurse performance were selected, including medication errors, patient complaints, patient falls, and nurses' self-report of fatigue. Nurse managers agreed to aggregate this data separately for the 2-week study period, and also arranged to ask study participants if they felt fatigued at the end of each shift.


A pilot of the data collection tools was conducted. Overall, 178 nurses were randomly selected to participate. Data was completed for 62% of shifts, with no difficulty using the tools identified by participants or managers. Instructions clarifying the length of the study period and the expectation regarding study participation were added to the data collection tools. Data from the pilot was analyzed using correlation and regression statistics. No significant difference was found between the performance of 8- and 12-hour shift nurses.


The actual study was conducted several months following the pilot. Systematic sampling techniques were used to select nurses to participate in the study. As there are few nurses regularly scheduled to work 8 hours on inpatient units at Forsyth, all of the nurses assigned to work this schedule on these units during the study period volunteered to participate. Every third 12-hour shift nurse on each inpatient unit was selected for the study. A total of 256 nurses participated in the study; 189 worked 12-hour shifts and 67 worked 8-hour shifts. Each of the nurses completed a log of their hours of work using the data collection tool. Hours of work were verified by nurse managers by comparing the logs with payroll reports. The nurse managers collected data each day on errors, falls, complaints, and self-reports of fatigue on the data collection tool. The study was conducted over 2 weeks. Data collection was completed on 80% of the nurses selected to participate.


Data analysis

In total, 245 female nurses and 11 male nurses participated in the study. Of these, 64 female nurses and three male nurses were regularly scheduled to work 8-hour shifts, and 181 female nurses and eight male nurses were regularly scheduled to work 12-hour shifts. The mean age of the 8-hour shift sample was 43.15, while the mean age of the 12-hour shift sample was 37.32. Mean years of experience for the 8-hour shift sample was 16.08, whereas mean years of experience for the 12-hour shift sample was 10.26.


The main purpose of this study was a comparison of performance and shift schedules by the evaluation of three variables. The first variable was that there's no relationship between working 12-hour shifts and 8-hour shifts as measured by collection of self-reports of fatigue. For this question, the Wilcoxon Rank Sum (WRS) test was performed to investigate whether significant differences occur in the mean number of fatigue days per shift. The same analysis was repeated using a contingency table approach. A logistic regression was performed to examine the probability of fatigue due to shift work. The second variable was that there's no relationship between the number of errors and working 12-hour shifts versus 8-hour shifts. The WRS test was used to investigate whether significant differences occur in mean number of errors per shift. The same analysis was repeated using Poisson regression. For the purpose of data analysis medication errors, falls and complaints were combined into one category called errors. This was necessary due to the relatively low number of errors reported. For the third variable, whether differences occur in the relationship between fatigue and errors from shift to shift, Spearman correlations were performed within shifts, as this would indicate if any positive relationship existed between the variables.


Data analysis demonstrated a relationship between self-reports of fatigue and the 8-hour shift for all measures. The odds of self-report of fatigue for the 8-hour shift nurses in the study were 2.38 times that of the 12-hour shift nurses, controlling for the effects of day, experience, and age. No relationship was found between the number of mean errors and shift in this data analysis, and no significant correlation between fatigue and errors were demonstrated. As this last result was unexpected, a detailed evaluation of fatigue days and errors per day was conducted using descriptive statistics. No definitive reason for this result was found. The difference in sample size between 8- and 12-hour shift nurses in this study, the relatively low number of errors reported (0% to 3% per day), and the fact that fatigue was collected only at the end of the shift may be factors that contribute to this result.


No difference determined

This investigation found no statistical difference in errors made by nurses regularly working 8-hour shifts and nurses regularly working 12-hour shifts. The design of the study enabled investigators to distinguish between a regular schedule of 12-hour shifts and nurses required to work additional, longer, or unexpected shifts due to staffing problems or other emergencies. The hospital doesn't mandate overtime, and the number of nurses who reported working overtime in the course of the study was relatively low, with only 21% of study participants reported as working more than 40 hours in a week. This may have contributed to the result. Studies involving the effects of long hours of work due to staffing emergencies, mandatory overtime, or multiple extra shifts may have different results.


Fatigue was measured by self-report by nurses at the end of the shift. There was no measurement of fatigue at the beginning of the shift. Collecting and evaluating demographic data such as hours of sleep, the number of children at home, and the drive time to work may provide further information. Nurse job satisfaction also wasn't measured as a part of this study. Adding this variable may be revealing especially as 12-hour shift nurses report high satisfaction with their work schedule. Collecting data regarding workload and patient acuity is suggested for future study. Replication at other hospitals and with a larger sample size, especially a more equal sample of 8- and 12-hour shift nurses, is also recommended.




1. Page A, ed. Keeping Patients Safe: Transforming The Work Environment of Nurses. Washington, DC: The National Academies Press; 2004:2-14. [Context Link]


2. Rogers A, et al. The working hours of hospital staff nurses and patient safety. Health Affairs. 2004;23(4):202-212. [Context Link]