Nurse-Patient Ratios as a Patient Safety Strategy
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Nurse–Patient Ratios as a Patient Safety Strategy
A Systematic Review
Paul G. Shekelle, MD, PhD
A small percentage of patients die during hospitalization or shortly
thereafter, and it is widely believed that more or better nursing care
could prevent some of these deaths. The author systematically
reviewed the evidence about nurse staffing ratios and in-hospital
death through September 2012. From 550 titles, 87 articles were
reviewed and 15 new studies that augmented the 2 existing re-
views were selected. The strongest evidence supporting a causal
relationship between higher nurse staffing levels and decreased
inpatient mortality comes from a longitudinal study in a single
hospital that carefully accounted for nurse staffing and patient
comorbid conditions and a meta-analysis that found a “dose–
response relationship” in observational studies of nurse staffing and
death. No studies reported any serious harms associated with an
increase in nurse staffing. Limiting any stronger conclusions is the
lack of an evaluation of an intervention to increase nurse staffing
ratios. The formal costs of increasing the nurse–patient ratio cannot
be calculated because there has been no evaluation of an inten-
tional change in nurse staffing to improve patient outcomes.
Ann Intern Med. 2013;158:404-409. www.annals.org
For author affiliation, see end of text.
T HE P ROBLEM
A small percentage of hospitalized patients die during
or shortly after hospitalization. Evidence suggests that
some proportion of these deaths could probably be pre-
vented with more nursing care. For example, in 1 early
study of 232 342 surgical discharges from several Pennsyl-
vania hospitals, 4535 patients (2%) died within 30 days of
hospitalization; the investigators estimated that the differ-
ence between 4:1 and 8:1 patient–nurse ratios may be ap-
proximately 1000 deaths in a group of this size (1). Other
studies have produced roughly similar estimates, namely
approximately 1 to 5 fewer deaths per 1000 inpatient days
with more nurse staffing per patient (2– 4). The rationale
for suggesting that increasing the ratio of registered nurses
(RNs) to patients will lead to decreased illness or mortality
rates rests on the belief that improved attention to patients
is the critical factor. This systematic review examined the
evidence on the effects of interventions aimed at increasing
nurse–patient ratios on patient illness and death.
P ATIENT S AFETY S TRATEGIES
There has been no evaluation of an intentional change
in RN staffing to improve patient outcomes; therefore, the
patient safety strategy referred to in this article remains
somewhat unclear. Most studies have been cross-sectional
or longitudinal assessments of differences in nursing staff
variables, with the most commonly assessed measure being
the proportion of RN time per some measure of inpatient
load and the most commonly assessed outcome being mor-
tality. However, many other factors have been proposed as
being causal with respect to the relationship between nurs-
ing care and reductions in hospital mortality, potentially in
addition to or instead of a simple nurse–patient ratio.
These factors include measures of nursing burnout, job
satisfaction, teamwork, nurse turnover, nursing leadership
in hospitals, and nurse practice environment.
Several research groups have proposed conceptual
frameworks to explain why more effective nursing care
may reduce inpatient mortality (5– 8). Underlying all of
these conceptual frameworks is the belief that surveillance
is a critical factor that can be improved with more staff,
better-educated staff, or a better working environment (9).
A representative framework by Aiken and colleagues (8)
posits that nurse–patient ratios, along with staffing skill
mix, can lead to better surveillance, which, along with
many other factors, can influence the process of care and
lead to better patient outcomes (Figure 1).
R EVIEW P ROCESSES
Two existing reviews relevant to the topic were iden-
tified, by using methods described by Whitlock and col-
leagues (10). These reviews were supplemented by search-
ing the Web of Science for articles published from 2009
(the end date of the search from the most recent review) to
September 2012 that cited any of 4 key articles in this
field, including the older of the 2 reviews, and was limited
to studies published in English. For a complete description
of the search strategies, literature flow diagram, and evi-
dence tables, see the Supplement (available at www.annals
.org). The update search identified 546 titles, and 4 articles
came from reference mining. Titles and abstracts were re-
viewed and selected if they reported empirical data on the
relationship between nurse staffing ratios and mortality or
nursing-sensitive outcomes, such as pressure ulcers and fail-
ure to rescue. Because several cross-sectional studies have
assessed this relationship, only 1 additional cross-sectional
study was included for detailed review. The exception was
a cross-sectional study that evaluated a quasi-intervention
(11). Nine longitudinal studies were identified (12–20).
See also:
Web-Only
CME quiz (Professional Responsibility Credit)
Supplement
Annals of Internal MedicineSupplement
404 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) www.annals.org
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
A Systematic Review
Paul G. Shekelle, MD, PhD
A small percentage of patients die during hospitalization or shortly
thereafter, and it is widely believed that more or better nursing care
could prevent some of these deaths. The author systematically
reviewed the evidence about nurse staffing ratios and in-hospital
death through September 2012. From 550 titles, 87 articles were
reviewed and 15 new studies that augmented the 2 existing re-
views were selected. The strongest evidence supporting a causal
relationship between higher nurse staffing levels and decreased
inpatient mortality comes from a longitudinal study in a single
hospital that carefully accounted for nurse staffing and patient
comorbid conditions and a meta-analysis that found a “dose–
response relationship” in observational studies of nurse staffing and
death. No studies reported any serious harms associated with an
increase in nurse staffing. Limiting any stronger conclusions is the
lack of an evaluation of an intervention to increase nurse staffing
ratios. The formal costs of increasing the nurse–patient ratio cannot
be calculated because there has been no evaluation of an inten-
tional change in nurse staffing to improve patient outcomes.
Ann Intern Med. 2013;158:404-409. www.annals.org
For author affiliation, see end of text.
T HE P ROBLEM
A small percentage of hospitalized patients die during
or shortly after hospitalization. Evidence suggests that
some proportion of these deaths could probably be pre-
vented with more nursing care. For example, in 1 early
study of 232 342 surgical discharges from several Pennsyl-
vania hospitals, 4535 patients (2%) died within 30 days of
hospitalization; the investigators estimated that the differ-
ence between 4:1 and 8:1 patient–nurse ratios may be ap-
proximately 1000 deaths in a group of this size (1). Other
studies have produced roughly similar estimates, namely
approximately 1 to 5 fewer deaths per 1000 inpatient days
with more nurse staffing per patient (2– 4). The rationale
for suggesting that increasing the ratio of registered nurses
(RNs) to patients will lead to decreased illness or mortality
rates rests on the belief that improved attention to patients
is the critical factor. This systematic review examined the
evidence on the effects of interventions aimed at increasing
nurse–patient ratios on patient illness and death.
P ATIENT S AFETY S TRATEGIES
There has been no evaluation of an intentional change
in RN staffing to improve patient outcomes; therefore, the
patient safety strategy referred to in this article remains
somewhat unclear. Most studies have been cross-sectional
or longitudinal assessments of differences in nursing staff
variables, with the most commonly assessed measure being
the proportion of RN time per some measure of inpatient
load and the most commonly assessed outcome being mor-
tality. However, many other factors have been proposed as
being causal with respect to the relationship between nurs-
ing care and reductions in hospital mortality, potentially in
addition to or instead of a simple nurse–patient ratio.
These factors include measures of nursing burnout, job
satisfaction, teamwork, nurse turnover, nursing leadership
in hospitals, and nurse practice environment.
Several research groups have proposed conceptual
frameworks to explain why more effective nursing care
may reduce inpatient mortality (5– 8). Underlying all of
these conceptual frameworks is the belief that surveillance
is a critical factor that can be improved with more staff,
better-educated staff, or a better working environment (9).
A representative framework by Aiken and colleagues (8)
posits that nurse–patient ratios, along with staffing skill
mix, can lead to better surveillance, which, along with
many other factors, can influence the process of care and
lead to better patient outcomes (Figure 1).
R EVIEW P ROCESSES
Two existing reviews relevant to the topic were iden-
tified, by using methods described by Whitlock and col-
leagues (10). These reviews were supplemented by search-
ing the Web of Science for articles published from 2009
(the end date of the search from the most recent review) to
September 2012 that cited any of 4 key articles in this
field, including the older of the 2 reviews, and was limited
to studies published in English. For a complete description
of the search strategies, literature flow diagram, and evi-
dence tables, see the Supplement (available at www.annals
.org). The update search identified 546 titles, and 4 articles
came from reference mining. Titles and abstracts were re-
viewed and selected if they reported empirical data on the
relationship between nurse staffing ratios and mortality or
nursing-sensitive outcomes, such as pressure ulcers and fail-
ure to rescue. Because several cross-sectional studies have
assessed this relationship, only 1 additional cross-sectional
study was included for detailed review. The exception was
a cross-sectional study that evaluated a quasi-intervention
(11). Nine longitudinal studies were identified (12–20).
See also:
Web-Only
CME quiz (Professional Responsibility Credit)
Supplement
Annals of Internal MedicineSupplement
404 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) www.annals.org
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
Four simulation studies reported on costs, and 1 systematic
review article was included (21–25). Two frameworks
were also included (6, 7). No experimental studies were
identified.
The assessment of multiple systematic reviews
(AMSTAR) criteria was used to assess the quality of the
systematic reviews (26). Only criteria relevant to a partic-
ular review were applied; for example, 2 of the 11
AMSTAR criteria are only applicable to reviews that in-
volve meta-analysis. In addition, the AMSTAR criteria re-
quiring a list of all excluded studies were not applied. New
studies were not formally assessed for study quality, but
their strengths and limitations are discussed later.
This review was supported by the Agency for Health-
care Research and Quality, which had no role in the selec-
tion or review of the evidence or the decision to submit
this manuscript for publication.
B ENEFITS AND H ARMS
Benefits
Two recent relevant systematic reviews on this topic, a
meta-analysis (27) and a narrative review (28), respectively
scored 10 out of 10 relevant criteria and 7 out of 9 relevant
criteria according to AMSTAR.
The meta-analysis included 28 studies, of which 17
were cohort studies, 7 were cross-sectional studies, and 4
were case– control studies (no experimental studies were
identified). Most were U.S. studies, and the average level of
staffing was 3.0 patients per RN for the intensive care unit
(ICU) setting, 4.0 patients per RN in the surgical setting,
and 4.4 patients per RN for the medical setting. It found a
consistent relationship between higher RN staffing and
lower hospital-related mortality: An increase of 1 RN full-
time equivalent (FTE) per patient day was related to a 9%
reduction in the odds of death in the ICU, a 16% reduc-
tion in the surgical setting, and a 6% reduction in the
medical setting. With respect to other outcomes, lower
rates of hospital-acquired pneumonia, pulmonary failure,
unplanned extubation, failure to rescue, and nosocomial
bloodstream infections were related to higher RN staffing
in pooled analyses of several studies. However, several
other outcomes that were presumed to have strong sensi-
tivity to nurse staffing levels did not show consistent rela-
tionships, including falls, pressure ulcers, and urinary tract
infections.
The authors also conducted an indirect analysis of the
potential for a dose–response relationship. This analysis
assessed the effect across studies of additional RNs per
shift. In each case, comparisons of quartiles of nurse staff-
ing levels showed the expected relationship (Figure 2). In
other words, if the relationship between nurse staffing and
mortality is causal, the difference in the risk for death
should be greater between the first and third quartiles of
nurse staffing than it is between the first and second quar-
tiles because the difference in staffing between the first and
third quartiles is greater than that between the first and
second quartiles.
The authors of the meta-analysis concluded that a
consistent relationship has been shown but identified sev-
eral limitations in the literature with respect to establishing
Key Summary Points
Cross-sectional studies, mostly in intensive care unit or
postsurgical settings, support a relationship between
the number of nurses staffed per patient and inpatient
mortality.
The strongest evidence supporting a causal relationship
between higher nurse staffing levels and decreased inpa-
tient mortality comes from a longitudinal study in a single
hospital that carefully accounted for nurse staffing levels
and found decreases in mortality of 2% to 7%.
Limiting any stronger conclusions is the lack of an evalua-
tion of an intervention to increase nurse staffing ratios.
Figure 1. Hospital organization, nursing organization, and patient outcomes.
Hospital organization
Process of care
Medical staff qualifications
Nurse
outcomes
Patient
outcomes
Organizational support for
nursing care
Resource adequacy
Nurse autonomy
Nurse control
Nurse–physician relations
Nurse–patient ratios/
staffing skill mix
Surveillance/early
detection of complications
From reference 8, with permission.
SupplementNurse–Patient Ratios as a Patient Safety Strategy
www.annals.org 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) 405
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
review article was included (21–25). Two frameworks
were also included (6, 7). No experimental studies were
identified.
The assessment of multiple systematic reviews
(AMSTAR) criteria was used to assess the quality of the
systematic reviews (26). Only criteria relevant to a partic-
ular review were applied; for example, 2 of the 11
AMSTAR criteria are only applicable to reviews that in-
volve meta-analysis. In addition, the AMSTAR criteria re-
quiring a list of all excluded studies were not applied. New
studies were not formally assessed for study quality, but
their strengths and limitations are discussed later.
This review was supported by the Agency for Health-
care Research and Quality, which had no role in the selec-
tion or review of the evidence or the decision to submit
this manuscript for publication.
B ENEFITS AND H ARMS
Benefits
Two recent relevant systematic reviews on this topic, a
meta-analysis (27) and a narrative review (28), respectively
scored 10 out of 10 relevant criteria and 7 out of 9 relevant
criteria according to AMSTAR.
The meta-analysis included 28 studies, of which 17
were cohort studies, 7 were cross-sectional studies, and 4
were case– control studies (no experimental studies were
identified). Most were U.S. studies, and the average level of
staffing was 3.0 patients per RN for the intensive care unit
(ICU) setting, 4.0 patients per RN in the surgical setting,
and 4.4 patients per RN for the medical setting. It found a
consistent relationship between higher RN staffing and
lower hospital-related mortality: An increase of 1 RN full-
time equivalent (FTE) per patient day was related to a 9%
reduction in the odds of death in the ICU, a 16% reduc-
tion in the surgical setting, and a 6% reduction in the
medical setting. With respect to other outcomes, lower
rates of hospital-acquired pneumonia, pulmonary failure,
unplanned extubation, failure to rescue, and nosocomial
bloodstream infections were related to higher RN staffing
in pooled analyses of several studies. However, several
other outcomes that were presumed to have strong sensi-
tivity to nurse staffing levels did not show consistent rela-
tionships, including falls, pressure ulcers, and urinary tract
infections.
The authors also conducted an indirect analysis of the
potential for a dose–response relationship. This analysis
assessed the effect across studies of additional RNs per
shift. In each case, comparisons of quartiles of nurse staff-
ing levels showed the expected relationship (Figure 2). In
other words, if the relationship between nurse staffing and
mortality is causal, the difference in the risk for death
should be greater between the first and third quartiles of
nurse staffing than it is between the first and second quar-
tiles because the difference in staffing between the first and
third quartiles is greater than that between the first and
second quartiles.
The authors of the meta-analysis concluded that a
consistent relationship has been shown but identified sev-
eral limitations in the literature with respect to establishing
Key Summary Points
Cross-sectional studies, mostly in intensive care unit or
postsurgical settings, support a relationship between
the number of nurses staffed per patient and inpatient
mortality.
The strongest evidence supporting a causal relationship
between higher nurse staffing levels and decreased inpa-
tient mortality comes from a longitudinal study in a single
hospital that carefully accounted for nurse staffing levels
and found decreases in mortality of 2% to 7%.
Limiting any stronger conclusions is the lack of an evalua-
tion of an intervention to increase nurse staffing ratios.
Figure 1. Hospital organization, nursing organization, and patient outcomes.
Hospital organization
Process of care
Medical staff qualifications
Nurse
outcomes
Patient
outcomes
Organizational support for
nursing care
Resource adequacy
Nurse autonomy
Nurse control
Nurse–physician relations
Nurse–patient ratios/
staffing skill mix
Surveillance/early
detection of complications
From reference 8, with permission.
SupplementNurse–Patient Ratios as a Patient Safety Strategy
www.annals.org 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) 405
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
that this relationship is causal. The authors ultimately con-
cluded that the arguments for a causal relationship are
“mixed,” and they called for future research to address the
role of nurse staffing and competence on the effectiveness
of patient care, “taking greater cognizance of other relevant
factors such as patient and hospital characteristics and
quality of medical care” (27).
The narrative review identified literature published
through 2009 and was restricted to studies that used
hospital-related mortality as the outcome; the authors
identified 17 studies (10 of which were not included in the
first review and 7 that were published since 2007) (28).
Although this review was narrative, the 2 reviews had
broadly similar results: 14 of 17 studies found a statistically
significant relationship between nurse staffing variables and
lower mortality rates. In addition, the narrative review
identified mixed findings for mortality among 5 studies
assessing the characteristics of the nurse work environment
and work relationships, 3 studies assessing nurses’ re-
sponses to work and the work environment (for example,
burnout), and 7 studies assessing nurses’ educational prep-
aration and experience. Only 1 study, which had a cross-
sectional design, assessed nursing process-of-care variables;
it found a relationship between the use of care maps and
lower hospital-associated mortality, with an estimated ef-
fect size of 10 fewer deaths per 1000 acute medicine dis-
charged patients. Like the meta-analysis, the narrative re-
view concluded that a strong relationship exists but more
research is needed to understand the reasons why this re-
lationship between higher nurse staffing and lower hospital
mortality may be causal (that is, they called for a theoret-
ical model that explains the relationship in ways that can
be tested and refined).
Thus, these 2 reviews came to broadly similar conclu-
sions. Mostly cross-sectional studies consistently report
that higher RN staffing is related to lower hospital-related
mortality.
However, many factors can confound the observed re-
lationship. In cross-sectional studies, hospitals that are
“better” in other ways may also be better staffed with more
RNs. For example, 1 published study of electronic health
record implementation showed that hospitals with elec-
tronic health records have higher nurse staffing ratios and
lower patient mortality (29). If the cross-sectional relation-
ship is confounded, then critics worry that adoption of
fixed nurse–patient ratios will not necessarily lead to better
health outcomes, that such a policy is “an inflexible solu-
tion that is unlikely to lead to optimal use of resources” (30).
The results of the updated search are as follows. Nine
longitudinal studies and one new systematic review (12–
20, 25) were identified. The systematic review included
studies that assessed nurse staffing ratios and outcomes re-
stricted to adult ICU settings (25) and reached conclusions
similar to the previous reviews: a consistent relationship
between increased nurse staffing and better patient out-
comes in observational studies, evidence that falls short of
causality. One longitudinal study narratively reported that
increased nurse staffing was related to “significantly (P
0.01) decreased rates of decubiti, pneumonia, and sepsis,”
but data were not presented (20). The cross-sectional study
addresses the effect of an “intervention” to change nurse
staffing ratios, implemented in response to a 2004 Califor-
nia law requiring minimum nurse–patient ratios in acute
care hospitals (11). This legislation mandated patient–
nurse staffing levels of 5:1, 4:1, and 2:1 for medical or
surgical units, pediatric units, and ICUs, respectively. The
California legislative mandate does not require nurse staff-
ing to be met with RNs (that is, licensed vocational [prac-
tical] nurses can also meet the mandate).
Aiken and colleagues (11) assessed the relationship be-
tween nurse staffing and mortality in 2006, 2 years after
the California mandate, comparing data from California
with those of 2 states without mandates, New Jersey and
Pennsylvania. Data about workloads were drawn from a
survey of RNs in the 3 states (22 336 nurses in total); the
response rate was 35.4%. Hospital data came from the
American Hospital Association, and patient and outcome
data came from state hospital discharge databases.
The authors reported that their survey data showed
substantial adherence to the California mandate, with 88%
of medical or surgical nurses, 85% of pediatric nurses, and
85% of ICU nurses reporting that the staffing of their last
Figure 2. Pooled odds ratio of quartiles of nurse staffing levels.
Quartiles of Patients/RN per Shift
All patients
1 vs. 2
1 vs. 3
1 vs. 4
2 vs. 3
2 vs. 4
3 vs. 4
Intensive care units
2 vs. 3
Medical patients
1 vs. 2
Surgical patients
1 vs. 3
1 vs. 4
2 vs. 3
2 vs. 4
3 vs. 4
Odds Ratio
of Death*
(95% CI)
Odds Ratio of Death*
0.94 (0.92–0.95)
0.76 (0.71–0.81)
0.62 (0.59–0.66)
0.81 (0.76–0.87)
0.66 (0.63–0.70)
0.82 (0.76–0.88)
0.94 (0.92–0.97)
0.94 (0.92–0.95)
0.76 (0.70–0.82)
0.62 (0.58–0.66)
0.80 (0.74–0.87)
0.65 (0.61–0.70)
0.81 (0.75–0.88)
0.5 1
Odds ratios are based on pooled analysis consistent across the studies
(heterogeneity not significant). From reference 27, with permission.
RN registered nurse.
Supplement Nurse–Patient Ratios as a Patient Safety Strategy
406 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) www.annals.org
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
cluded that the arguments for a causal relationship are
“mixed,” and they called for future research to address the
role of nurse staffing and competence on the effectiveness
of patient care, “taking greater cognizance of other relevant
factors such as patient and hospital characteristics and
quality of medical care” (27).
The narrative review identified literature published
through 2009 and was restricted to studies that used
hospital-related mortality as the outcome; the authors
identified 17 studies (10 of which were not included in the
first review and 7 that were published since 2007) (28).
Although this review was narrative, the 2 reviews had
broadly similar results: 14 of 17 studies found a statistically
significant relationship between nurse staffing variables and
lower mortality rates. In addition, the narrative review
identified mixed findings for mortality among 5 studies
assessing the characteristics of the nurse work environment
and work relationships, 3 studies assessing nurses’ re-
sponses to work and the work environment (for example,
burnout), and 7 studies assessing nurses’ educational prep-
aration and experience. Only 1 study, which had a cross-
sectional design, assessed nursing process-of-care variables;
it found a relationship between the use of care maps and
lower hospital-associated mortality, with an estimated ef-
fect size of 10 fewer deaths per 1000 acute medicine dis-
charged patients. Like the meta-analysis, the narrative re-
view concluded that a strong relationship exists but more
research is needed to understand the reasons why this re-
lationship between higher nurse staffing and lower hospital
mortality may be causal (that is, they called for a theoret-
ical model that explains the relationship in ways that can
be tested and refined).
Thus, these 2 reviews came to broadly similar conclu-
sions. Mostly cross-sectional studies consistently report
that higher RN staffing is related to lower hospital-related
mortality.
However, many factors can confound the observed re-
lationship. In cross-sectional studies, hospitals that are
“better” in other ways may also be better staffed with more
RNs. For example, 1 published study of electronic health
record implementation showed that hospitals with elec-
tronic health records have higher nurse staffing ratios and
lower patient mortality (29). If the cross-sectional relation-
ship is confounded, then critics worry that adoption of
fixed nurse–patient ratios will not necessarily lead to better
health outcomes, that such a policy is “an inflexible solu-
tion that is unlikely to lead to optimal use of resources” (30).
The results of the updated search are as follows. Nine
longitudinal studies and one new systematic review (12–
20, 25) were identified. The systematic review included
studies that assessed nurse staffing ratios and outcomes re-
stricted to adult ICU settings (25) and reached conclusions
similar to the previous reviews: a consistent relationship
between increased nurse staffing and better patient out-
comes in observational studies, evidence that falls short of
causality. One longitudinal study narratively reported that
increased nurse staffing was related to “significantly (P
0.01) decreased rates of decubiti, pneumonia, and sepsis,”
but data were not presented (20). The cross-sectional study
addresses the effect of an “intervention” to change nurse
staffing ratios, implemented in response to a 2004 Califor-
nia law requiring minimum nurse–patient ratios in acute
care hospitals (11). This legislation mandated patient–
nurse staffing levels of 5:1, 4:1, and 2:1 for medical or
surgical units, pediatric units, and ICUs, respectively. The
California legislative mandate does not require nurse staff-
ing to be met with RNs (that is, licensed vocational [prac-
tical] nurses can also meet the mandate).
Aiken and colleagues (11) assessed the relationship be-
tween nurse staffing and mortality in 2006, 2 years after
the California mandate, comparing data from California
with those of 2 states without mandates, New Jersey and
Pennsylvania. Data about workloads were drawn from a
survey of RNs in the 3 states (22 336 nurses in total); the
response rate was 35.4%. Hospital data came from the
American Hospital Association, and patient and outcome
data came from state hospital discharge databases.
The authors reported that their survey data showed
substantial adherence to the California mandate, with 88%
of medical or surgical nurses, 85% of pediatric nurses, and
85% of ICU nurses reporting that the staffing of their last
Figure 2. Pooled odds ratio of quartiles of nurse staffing levels.
Quartiles of Patients/RN per Shift
All patients
1 vs. 2
1 vs. 3
1 vs. 4
2 vs. 3
2 vs. 4
3 vs. 4
Intensive care units
2 vs. 3
Medical patients
1 vs. 2
Surgical patients
1 vs. 3
1 vs. 4
2 vs. 3
2 vs. 4
3 vs. 4
Odds Ratio
of Death*
(95% CI)
Odds Ratio of Death*
0.94 (0.92–0.95)
0.76 (0.71–0.81)
0.62 (0.59–0.66)
0.81 (0.76–0.87)
0.66 (0.63–0.70)
0.82 (0.76–0.88)
0.94 (0.92–0.97)
0.94 (0.92–0.95)
0.76 (0.70–0.82)
0.62 (0.58–0.66)
0.80 (0.74–0.87)
0.65 (0.61–0.70)
0.81 (0.75–0.88)
0.5 1
Odds ratios are based on pooled analysis consistent across the studies
(heterogeneity not significant). From reference 27, with permission.
RN registered nurse.
Supplement Nurse–Patient Ratios as a Patient Safety Strategy
406 5 March 2013 Annals of Internal Medicine Volume 158 • Number 5 (Part 2) www.annals.org
Downloaded from https://annals.org by India: ANNALS Sponsored user on 05/15/2019
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