TABLE 1.

Number of included primary studies, methodologies, patient outcomes, quality assessment score and further descriptors reviews

Authors	Number of included primary studies	Research objective	Design	Period	Patient setting	Input variables—nurse staffing measures a	Output variables—considered NSPOs (min 1, max 29)	Quality Assessment Category [weighted score]
Bae and Fabry (2014) 36	11 b	To evaluate systematically the effect of nurse overtime and long work hours on nurse and patient outcomes	Systematic literature review	2000‐2013	Acute care, nursing homes, and other health care settings	Shift length (daily) work hours Weekly work hours Number of shifts per week Breaks Overtime Voluntary overtime Mandatory overtime On call	Medication errors Falls Decubitus ulcers Failure to rescue Nurse perceptions of quality Hypoglycemic events Perceived adverse events Errors or near misses Pneumonia deaths Patient dissatisfaction Nosocomial infection Abdominal aortic aneurysm postoperative deaths Mortality Central‐line‐associated blood stream infection Urinary tract infection Ventilator‐associated pneumonia Gastrointestinal bleedings Shock cardiac arrest Sepsis	Moderate [0.463]
Chin (2013) 37	12	To examine the empirical evidence on the relationship between nurse staffing and quality of care in acute care settings	Systematic literature review	2002‐2012	Acute care adult setting	Nurse staffing: Nurse‐to‐patient ratio Nursing hours per patient day RN hours per patient day Total number of nursing care hours Total of hours of RNs, LPNs and NAs Total hours of nursing care provided Total hours worked by nurses Ratio of licensed nurses to patients Skill mix: Ratio of RNs to other nursing staff Ratio of RN hours to all nursing care hours	Quality of care (30‐day) mortality Failure to rescue Falls Sepsis Gastrointestinal bleeding Pressure sore/pressure ulcer/decubitus Congestive heart failure Prolonged length of stay Pneumonia Deep vein thrombosis Urinary tract infections (Wound) infection Shock and cardiac arrest Length of stay	Moderate [0.352]
Driscoll et al (2018) 17	31	To examine the association between nurse staffing levels and nursing‐sensitive patient outcomes in acute specialist units	Systematic review and meta‐analysis	2006‐2017	Acute care (specialist units)	Ratio of the number of nurses (per shift or over a 24‐h period) divided by the number of beds occupied by patients over the same period Number of nursing hours per patient bed days	Mortality Failure to rescue Shock Cardiac arrest Unplanned extubation Hospital‐acquired pneumonia Respiratory failure Surgical bleeding Heart failure/fluid overload Catheter‐associated urinary tract infections Pressure sores Patient falls Nosocomial bloodstream infections Medication error Length of stay Hospital‐acquired sepsis Deep vein thrombosis Central nervous system complication Death Wound infection Pulmonary failure Metabolic derangement Pain control Unplanned readmission	Moderate [0.597]
Donaldson and Shapiro (2010) 38	6 c	To examine the impact of California's nurse‐to‐patient ratios on patient care cost, quality, and outcomes in acute care hospitals	Literature Synthesis	2004‐2009	Acute care	RN hours of direct care per patient day RN productive hours of care per patient day RN registry hours of direct care per patient day Ratio RN to patient Hours of RN care per patient day Skill mix LVN	Falls incidence Falls with injury % prevalence hospital‐acquired pressure ulcer (HAPU) % prevalence restraint use Length of stay Incidence failure to rescue Incidence HAPU Incidence hospital‐acquired infections Incidence DVT Incidence postop pneumonia Incidence postop sepsis Reported medication errors	High [0.889]
Griffiths et al (2014) 39	35 d	To provide evidence on which patient safety outcomes are associated with nurse and health care assistant staffing levels and skill mix by answering the following two questions: What outcomes are associated with tasks undertaken by registered nurses, health care assistants (HCA), and other staff? Which outcomes should be used as indicators of safe staffing?	Systematic literature review	1993‐2014	Acute care adult setting	Nurse‐to‐patient ratios	Mortality Fall/injury Pressure ulcer Adverse drug event Pneumonia Urinary tract infection Wound infection Sepsis Upper gastrointestinal bleeding Pulmonary failure Shock/cardiac failure Central nervous system complications Deep vein thrombosis Bloodstream infection Physical/metabolic derangement Length of stay Cost Hospital‐acquired infections Failure to rescue Readmission Patient satisfaction Drug administration errors Lack of or inadequate nursing care Discharge preparation Emergency department (ED) visits MRSA infection	High [0.685]
Heslop and Lu (2014) 40	38	To report a concept analysis of nurse‐sensitive indicators within the applied context of the acute care setting	Concept analysis	2000‐2012	Acute care setting	Hours of nursing care per patient day Nurse staffing (staff mix, skill mix, and staff ratio)	Mortality Falls and falls with injury Pressure ulcer Nosocomial selective infection Nosocomial urinary tract infection Medication error Pneumonia Vein system complication Failure to rescue Restraint Sepsis Gastrointestinal bleeding Shock Patient/family satisfaction with nursing care Patient/family satisfaction with pain management Length of stay Waiting time for nursing care Unplanned hospital visits postdischarge Vital signs status, self‐care ability Symptom resolution/reduction	Moderate [0.344]
Hill (2017) 41	5	To provide evidence on whether registered nurse staffing levels affect patient mortality in acute secondary care settings	Systematic literature review	1994‐2014	Acute care setting	Nurse staffing levels, incl. nurse‐to‐patient ratios and nursing time	Mortality	Low [0.315]
Kane et al (2007) 6	96 (28 e )	To examine the association between RN staffing and patient outcomes in acute care hospitals	Systematic literature Review and meta‐analysis	1990‐2006	Acute care setting	RNs to patients	Hospital‐related mortality Failure to rescue Cardiac arrest Shock Unplanned extubation Respiratory failure Deep venous thrombosis Upper gastrointestinal bleeding Surgical bleeding Patient falls Pressure ulcers Nosocomial infection Urinary tract infection Hospital‐acquired pneumonia Nosocomial bloodstream Length of stay	High [0.764]
Min and Scott (2016) 42	14 f	To identify techniques used to measure nurse staffing and to evaluate the reliability, validity, and limitations of nursing hours per patient day (NHPPD)	Literature review	2002‐2015	Acute care setting	Nurse‐to‐patient ratios Full‐time equivalents Nursing hours per patient day Skill mix Nurse‐perceived staffing adequacy Nurse‐reported number of assigned patients	Risk‐adjusted 30‐d mortality Failure to rescue Rates of patient falls Injury falls Pneumonia Decubitus/pressure ulcer Mortality Quality scores	Moderate [0.407]
Olley et al (2018) 43	11 g	To evaluate and summarize available research on nurse staffing methods and relate these to outcomes under the following three overarching themes: Management of clinical risk, quality, and safety Development of a new or innovative staffing methodology Equity of nursing workload	Systematic literature review	2010‐2016	Acute care setting	Nurse‐to‐patient ratios	Mortality/inpatient deaths within 30 d of admission	Low [0.315]
Recio‐Saucedo et al (2017) 44	14	To undertake a systematic review of the literature on the impact of missed nursing care on outcomes in adults in acute hospital wards or in nursing homes	Systematic literature review	N/A (oldest study is from 2004, most recent study from 2016)	Acute care setting and nursing homes	Missed care/nursing care left undone based on surveys	Medication errors Bloodstream infections Pneumonia Urinary tract infections (UTIs) Nosocomial infections Patient falls Pressure ulcers Patient and/or carer experience and satisfaction ratings Patient safety Quality of nurse‐delivered care Critical incidents Adverse events Mortality 30‐day hospital readmission	Moderate [0.611]
Shekelle (2013) 45	17	To examine the evidence on the effects of interventions aimed at increasing nurse‐patient ratios on patient illness and death	Systematic literature review	2009‐2012	Acute care setting	Nurse‐to‐patient ratios	Mortality Failure to rescue Decubitus/pressure ulcer Pneumonia Sepsis Falls	Moderate [0.407]
Stalpers et al (2015) 1	17 h	To examine the relationships between characteristics of the nurse work environment and five nursing‐sensitive patient outcomes in hospitals	Systematic literature review	2004‐2012	Acute Care setting	Total nursing hours RN hours Proportion of registered nurses Temporary nurses Turnover	Delirium Malnutrition Pain Patient falls Pressure ulcers	Moderate [0.630]
Twigg et al (2015) 46	9	To review the literature on economic evaluations of nurse staffing and patient outcomes to see whether there is consensus that increasing nursing hours/skill mix is a cost‐effective way of improving patient outcomes	Systematic literature review	Until 2013	Acute Care setting	Ratio of required to actual nurse staffing hours Nursing hours per patient day Total RN hours per patient day Non‐RN hours per patient day Raising RN proportion to 75th percentile/raising nursing hours to 75th percentile Nursing FTE per patient day Split between overtime and nonovertime hours RN vacancy rate	Length of stay Presence of complications Acuity level Pulmonary failure Metabolic derangement Wound infection Deep vein thrombosis Pneumonia Urinary tract infection Pressure ulcer Sepsis Shock/cardiac arrest Gastrointestinal bleed Transfer to Intensive Care Unit Avoided deaths Avoided adverse outcomes Mortality Lives saved Failure to rescue Unplanned extubation Respiratory failure Falls Nosocomial infection Nosocomial blood stream infection Life years gained (based on differences in failure to rescue pre‐ and postintervention) Unplanned readmissions in 30 d ED visits in 30 d Quality of discharge teaching scale Readiness for hospital discharge scale	Moderate [0.630]
Unruh (2008) 47	21	To assess the impact of hospital nurse staffing levels on given patient, nurse, and financial outcomes	Literature Review	1980‐2006	Acute Care setting	Number of (registered/nonregistered) nurses or (registered/nonregistered) nursing hours per number of patients or patient days RN skill mix	Blood stream infections Cardiac arrest Shock Complications Falls Failure to rescue Medication errors Mortality Pneumonia Postoperative infections Patient satisfaction Pulmonary compromise Restraint use Skin breakdown Thrombosis Urinary tract infections Upper gastrointestinal bleeding	Low [0.093]

Abbreviations: DVT, deep vein thrombosis; ED, emergency department; FTE, full‐time equivalent; HAPU, hospital‐acquired pressure ulcer; HCA, health care assistant; LPN, licensed practical nurse; LVN, licensed vocational nurse; NA, nursing assistant; NHPPD, nursing hours per patient day; RN, registered nurse.

^aBased on reported list of included NSPOs (inclusion criteria). If not explicitly stated, we derived and aggregated staffing measures based on results and evidence tables from the included studies.

^b24 studies included in total, 11 reporting on patient outcomes.

^c12 studies included in total, six reporting on patient outcomes.

^d46 studies included in total, 35 related to our research question.

^e28 of 96 studies included in the meta‐analysis reported adjusted odds ratios and included studies were available.

^f17 studies included in total, 14 related to our research question.

^g21 studies included in total, 11 related to our research question.

^h29 studies included in total, 17 related to our research question (nurse staffing as independent variable).