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Address for correspondence: Peter B. Smulowitz, MD, MPH, Department of Emergency Medicine, Beth Israel Deaconess Medical Center, One Deaconess Road, WCC 2, Boston, MA 02215; 617-667-1708, fax 617-754-2350
Health care reform in Massachusetts improved access to health insurance, but the extent to which reform affected utilization of the emergency department (ED) for conditions potentially amenable to primary care is unclear. Our objective is to determine the relationship between health reform and ED use for low-severity conditions.
We studied ED visits, using a convenience sample of 11 Massachusetts hospitals for identical 9-month periods before and after health care reform legislation was implemented in 2006. Individuals most affected by the health reform law (the uninsured and low-income populations covered by the publicly subsidized insurance products) were compared with individuals unlikely to be affected by the legislation (those with Medicare or private insurance). Our main outcome measure was the rate of overall and low-severity ED visits for the study population and the comparison population during the period before and after health reform implementation.
Total visits increased from 424,878 in 2006 to 442,102 in 2008. Low-severity visits among publicly subsidized or uninsured patients decreased from 43.8% to 41.2% of total visits for that group (difference=2.6%; 95% confidence interval [CI] 2.25% to 2.85%), whereas low-severity visits for privately insured and Medicare patients decreased from 35.7% to 34.9% of total visits for that group (difference=0.8%; 95% CI 0.62% to 0.98%), for a difference in differences of 1.8% (95% CI 1.7% to 1.9%).
Although overall ED volume continues to increase, Massachusetts health reform was associated with a small but statistically significant decrease in the rate of low-severity visits for those populations most affected by health reform compared with a comparison population of individuals less likely to be affected by the reform. Our findings suggest that access to health insurance is only one of a multitude of factors affecting utilization of the ED.
Through a combination of individual mandates, employer assessments, insurance market reforms, and expansion of publicly subsidized insurance products, the program provided insurance coverage to an incremental 439,000 individuals as of March 31, 2008.
Altering health insurance can change patients' care-seeking behavior, but the effect on emergency department (ED) use is uncertain.
What question this study addressed
Did the Massachusetts health reform act, created in 2006 to increase coverage statewide, alter ED utilization for all conditions and low-acuity conditions?
What this study adds to our knowledge
When comparing the year before with the year after implementation, ED visits in 11 hospitals selected by convenience increased marginally. ED visits for lower-acuity conditions decreased slightly.
How this is relevant to clinical practice
Health insurance reform alone does not translate to a widespread change in ED use for low-acuity conditions.
Approximately 70% of the newly insured in Massachusetts obtained coverage through expansion of MassHealth, the state's Medicaid program (including an extension of children's eligibility from 200% to 300% of the federal poverty level) and enrollment in Commonwealth Care, a publicly subsidized option for those with low income who do not qualify for Medicaid.
Under Commonwealth Care, those individuals earning less than 150% of the federal poverty level receive fully subsidized insurance, whereas those earning between 150% and 300% of the federal povery level receive partially subsidized coverage on a sliding scale. The remaining newly insured obtained other private insurance coverage, with most receiving employer-sponsored insurance and the remainder purchasing unsubsidized insurance through the Commonwealth Connector, an independent public insurance exchange that offers a choice of health plan products for both the Commonwealth Care and Choice programs, with relatively standardized benefit packages.
The Commonwealth Choice program specifically is an unsubsidized health insurance option available through the Connector to people who are not eligible for Commonwealth Care or MassHealth (see Appendix E1, available online at http://www.annemergmed.com). This structure of subsidies and a health insurance exchange as a means to expanding health insurance coverage served as the model for the Patient Protection and Affordable Care Act recently passed by Congress.
The Massachusetts legislation has been successful in reducing financial barriers to accessing care. A 2008 Urban Institute survey showed that the expansion of health insurance in Massachusetts had the intended effect of reducing the influence of cost as a barrier for all adults and lower-income adults seeking necessary health care services and prescription drugs.
Although the legislation has reduced financial barriers to care, its effect on access to care and emergency department (ED) utilization is less clear. ED visits across the country have been burgeoning, increasing more than 9% from 1999 to 2007,
and decreasing ED crowding has been one of the anticipated benefits of health reform. This expectation may be due to the ED's role as a safety net for patients with nonurgent conditions who have no other source of care.
By increasing insurance coverage, Massachusetts health reform theoretically could facilitate access to ongoing primary care for the newly insured and thereby result in decreased ED utilization for services potentially amenable to timely primary care.
Despite Massachusetts having the most primary care physicians per capita in the United States, difficulties accessing primary care services have been well documented.
In 2007, about 1 in 5 adults in Massachusetts reported difficulty obtaining care because a physician's office or clinic was not accepting patients with their type of coverage or was not accepting new patients at all.
These problems are most severe in specific parts of the state with primary care shortages, including Cape Cod and parts of western Massachusetts. With this overburdened primary care system, it is unclear whether providing insurance coverage alone will be sufficient to improve access to primary care services. Furthermore, an individual's decision to utilize an ED is complex and not dependent solely on access to primary care, a function of both the nature and severity of the presenting complaint and the patient's experience with and access to other health care delivery settings.
For some individuals, lack of effective access to health care may be related to their lack of insurance. For others, barriers exist because of the high cost of care despite insurance. And for others, the decision to seek care in an ED may be due to lack of access to other sources of care. In all cases, the severity of underlying health problems, the convenience of ED hours, the ability to obtain a comprehensive evaluation and testing at one time in the ED, cultural views about seeking care through primary care or the ED, patient perceptions of severity of illness, and other educational, cultural, logistic, and psychosocial factors also affect this decision.
Thus, it still remains to be seen whether obtaining insurance or improved access to primary care will have a substantial effect in altering the patterns of ED use.
Goals of This Investigation
The goal of this study was to assess the effect of the Massachusetts health reform law on ED utilization for the group of individuals affected by health reform compared with utilization by a comparison group of individuals with private insurance or Medicare. We specifically compared ED utilization for all and for lower-severity visits, as well as visits for ambulatory care sensitive conditions. These are conditions “for which good outpatient care can potentially prevent the need for hospitalization or for which early intervention can prevent complications or more severe disease.”
We hypothesized that despite limited primary care availability in the state, health care reform would be associated with decreases in ED visits for low-severity conditions and reductions in ambulatory care sensitive visits and hospitalizations.
Materials and Methods
We used administrative billing data from a subset of Massachusetts hospitals for January 1, 2006, through September 30, 2008, to examine ED and hospital utilization during the year before and 2 years after the implementation of health reform. Specifically, we focused on rates of low- and high-severity ED visits, as well as rates of ambulatory care sensitive hospitalizations that resulted from ED visits. Although the health reform legislation was enacted in April 2006, enrollment into the publicly subsidized Commonwealth Care plans did not begin until October 1, 2006, and the individual mandate was not implemented until January 1, 2008. At that time, every individual in Massachusetts was required to have proof of health insurance or be subject to a $219 fine.
We used a pre-post difference in differences approach to compare rates of ED utilization among those who were most likely to be affected by health reform (the uninsured and low-income populations covered by the publicly subsidized insurance products, hereafter referred to as “publicly subsidized”) with rates among those unlikely to have been affected by health reform (eg, the commercially insured and Medicare populations).
We used administrative data from a convenience sample of 11 hospitals in Massachusetts. These included 4 tertiary care academic medical centers, 2 community hospitals, 3 safety net/community hospitals, and 2 safety net/tertiary care academic centers, with a combined annual ED volume of approximately 587,000 visits. These hospitals account for about 20% of ED visits in Massachusetts.
Because ED use varies seasonally and because we had data through October 2008 (9 months after the individual mandate took effect and 24 months after health reform was implemented), we elected to study 3 identical 9-month periods (January 1 to September 30) including the year before and the 2 years after the implementation of health reform (Figure 1).
Selection of Participants
Our intent in defining the study groups was to compare the rates of ED utilization for populations most likely to be affected by health reform with the rates among the commercially insured and Medicare populations who were unlikely to be affected during the periods before and after the implementation of health reform. We used this approach because the available data lacked individual identifiers that would allow for longitudinal tracking of a defined population. Health reform in Massachusetts expanded coverage principally through offering subsidized or free coverage through Commonwealth Care or MassHealth to those who were previously uninsured or received limited coverage from the state's uncompensated care pool. Under health reform, a new and smaller health safety net fund replaces the uncompensated care pool and provides coverage to selected low-income individuals who are not eligible for MassHealth or Commonwealth Care. In fiscal year 2009, there were 277,000 remaining health safety net users compared with 447,000 individuals in the uncompensated care pool in fiscal year 2006.
Before health reform, 3 groups composed those most likely to be affected by health reform: the uninsured (self-pay), enrollees in MassHealth, and those covered by the uncompensated care pool. After health reform, these patients fell into one of 4 coverage groups: uninsured (self-pay), MassHealth, Commonwealth Care, and the much smaller health safety net group. The MassHealth population specifically is included because a substantial portion of those newly insured through health reform acquired their insurance through MassHealth. Health reform simply increased the overall number of MassHealth enrollees. Thus, changes in ED utilization for the study group should reflect, at least in part, the effect of health reform on this population. The only group likely to have been affected whom we were unable to adequately track is those uninsured who enrolled in private plans through the private market or Commonwealth Connector. Of the 439,000 newly insured individuals, more than two thirds obtained coverage through MassHealth or Commonwealth Care, whereas the remainder obtained new employer-sponsored insurance or purchased coverage through Commonwealth Choice.
to classify visits as low, indeterminate, or high severity or unclassified. Unclassified diagnoses are those not captured in the initial algorithm. We defined a visit as high severity if the probability that ED care was needed was at least 75% for the visit's primary International Classification of Diseases, Ninth Revision (ICD-9), Clinical Modification diagnosis. We defined a visit as low severity if the probability of needing ED care was less than 25%. Visits between 25% and 75% probability were defined as indeterminate (Figure 2). The low-severity category should identify a group of diagnoses that could be more amenable to available primary care, but the severity categories, consistent with the initial intent of Billings et al,
Hospitalizations were identified by examining the disposition codes from the ED administrative data. We analyzed changes in overall hospitalization rates, rates of ED visits for ambulatory care sensitive conditions, and hospitalization rates for the ambulatory care sensitive ED visits as measured by the Agency for Healthcare Research and Quality's prevention quality indicators. We excluded prevention quality indicator admissions for chronic obstructive pulmonary disease and lower-extremity amputations among patients with diabetes because they required recognition of secondary diagnoses and our data included only the primary ICD-9 diagnosis.
Primary Data Analysis
We compared patient demographics for each of the 3 periods of the study groups with χ2 tests or t tests, as appropriate (Table 1).
We then examined how the implementation of health reform affected the distribution of ED visits by comparing the percentage of visits of low, indeterminate, and high severity across the 2 populations before and after the implementation of health reform. Our analyses rely on the assumption that the populations served by these hospitals remained relatively constant during the study period such that changes in the distribution of visits reflected changes in ED utilization patterns among the intervention and control groups. χ2 Tests were used to examine the outcomes of interest: changes in low-severity visits and ambulatory care sensitive visits and hospitalizations in the publicly subsidized/uninsured group compared with the comparison group from the period before health reform to the period after. All analyses were performed with SAS software (SAS Institute, Inc., Cary, NC).
The study was approved by the institutional review board at each participating institution.
Characteristics of Study Subjects
Individuals in the publicly subsidized/uninsured group were more likely to be male, younger, and nonwhite (Table 1). Overall ED visits increased by 4.1% from 2006 to 2008 (424,878 to 442,102). This includes an increase of 3.4% from 2006 to 2007 and an increase of 0.7% from 2007 to 2008. ED visits for the study population increased from 157,586 in the year before health reform to 159,649 in the year after full implementation of health reform. During the same period, visits for the comparison population less likely to be affected by health reform increased from 267,292 to 283,453 (Figure 3). In an analysis by type of hospital, overall visits in the study population decreased slightly for safety net hospitals (90,425 in period 1 to 88,834 in period 3), whereas visits at academic hospitals increased during that same period (38,827 to 43,051). Visits for the comparison population increased for both groups (91,525 to 95,632 for safety net hospitals, 113,648 to 125,735 for academic hospitals). These results must be interpreted with caution, however, because the decrease in safety net hospital visits in the study group is largely attributable to a single hospital, with 3 of the 5 safety net hospitals actually demonstrating an increase in visits from periods 1 to 3.
Low-severity visits for the group likely to be affected by health reform decreased from 43.8% of total group visits in 2006 to 41.2% in 2008 (difference=2.6%; P<.05). Low-severity visits in the comparison population decreased to a lesser extent, from 35.7% of visits to 34.9% (difference=0.8%; P<.05), for a difference in differences of 1.8% (P<.001) (Table 2) (Figure 4). In an analysis stratified by age, for the group less than 18 years old the difference in differences between the publicly subsidized/uninsured group and the comparison group was virtually zero. Hence, the large majority of the difference in low-severity visits between the study and comparison groups from period 1 to period 3 is attributable to the group of individuals at or over 18.
Table 2Overall ED visits and visit severity for the uninsured/publicly subsidized group and the comparison group.
Publicly Subsidized/Uninsured Group, Period
Comparison Group, Period
Difference in Difference Between Study Group and Comparison Group (95% CI)
In contrast, high-severity visits in the publicly subsidized/uninsured group decreased to a lesser extent than in the comparison group, although the decrease in each was still statistically significant (9.8% to 9.4%, P<.05 in the study group versus 12.2% to 11.6%, P<.05 in the comparison population, for a difference in differences of 0.2%, P<.001).
Table 3 shows rates of ED visits for ambulatory care sensitive conditions, as well as percentages of ED visits resulting in admissions for all conditions and for ambulatory care sensitive conditions. Overall hospitalizations after ED visits increased by 1.0% from 2006 to 2007 (20.0% of overall visits to 21.0%; P<.05) and by 0.2% from 2007 to 2008 (21.0% to 21.2%; P<.05).
Table 3ED visits for ambulatory care sensitive conditions and those resulting in hospitalization for all visits and for ambulatory care sensitive conditions.
Publicly Subsidized/Uninsured Group, Period
Comparison Group, Period
Difference in Difference Between Study Group and Comparison Group
Calculated Change From Period 1 to Period 3 (95% CI +/−)
Calculated Change From Period 1 to Period 3 (95% CI +/−)
No. ED visits for ambulatory care sensitive conditions (% of total visits)
−0.6 (−0.51 to −0.69)
−0.4 (−0.32 to −0.48)
−0.2 (−0.3 to −0.1)
No. ED visits resulting in hospitalization (% of total visits)
1.3 (1.15 to 1.45)
0.5 (0.33 to 0.67)
0.8 (0.6 to 0.10)
No. ED visits resulting in hospitalization for ambulatory care sensitive conditions (% of total ambulatory care sensitive visits)
Overall visits for ambulatory care sensitive conditions decreased by 0.6% in the publicly subsidized/uninsured group (3.7% of total visits to 3.1%; P<.05) and by 0.4% in the comparison group (4.4% to 4.0%; P<.05), for a difference in differences of 0.2% (P<.001). Hospitalizations for ambulatory care sensitive visits for the publicly subsidized/uninsured group increased by 6.7% after health reform (21.1% to 27.8% of total ambulatory care sensitive visits before and after; P<.05). The comparison group visits increased by 0.6% (57.8% to 58.4% of total ambulatory care sensitive visits; P<.05) after health reform. This accounts for a difference in difference of 6.1% (P<.001).
Our study is subject to several limitations. First, because we included only 1 year before and after health reform, longer-term studies will be needed to verify any trend in ED visit rates.
The chief limitation of this study is our inability to study longitudinally a specific population of enrollees before and after health reform. Instead, we relied on visit-level information from the ED and inferred differences by examining the changes in the percentage of visits for a population that was expected to be most affected by health reform. Additionally, because of limitations in our data we were unable to identify individuals who enrolled in private health insurance plans in the private market or through the Commonwealth Connector. Thus, some patients in the population likely to be affected by health reform were included in the commercially insured control population in the postreform period. This accounts for roughly one third of the newly insured in Massachusetts. It is plausible that these privately insured individuals would have better access to primary care and thus may influence our results by augmenting the decrease in lower-severity ED visits. Yet it is also plausible that obtaining insurance coverage could result in these individuals seeking ED care more often for lower-severity conditions. Hence, it is impossible to discern the magnitude of effect of this potential bias, and future studies will endeavor to eliminate this effect entirely.
The study is further limited by including a convenience sample of hospitals from Massachusetts. We included a mix of tertiary, academic, community, and safety net hospitals of a variety of sizes, though hospitals in the sample are more likely to be larger, and western Massachusetts is underrepresented. The other limitation of this convenience sample is that patients might have migrated to other hospitals even in similar geographic areas. Overall, the 4.1% increase in ED visits in our study mirrors the 4.6% increase observed on the state level. Future studies will endeavor to use data on a statewide level.
With respect to demographic characteristics, our results demonstrate changes in both groups from before to after health reform that may in part explain the changes in ED utilization. Because the study sample does not include the entire state, we cannot be certain that the hospitals included in our study are not experiencing a shift in race or other demographic characteristics as an unintended consequence of health reform. Nevertheless, even though we are not able to discern the effect of race versus insurance, the findings of an overall increase in ED use and a modest decrease in lower-severity visits are noteworthy. This study can demonstrate only a temporal association of findings with health reform and does not seek to imply causality.
Finally, it is possible that much or all of the decrease in low-severity visits in the study population could be due to an increase of 3.2% in the number of unclassified visits from 2006 to 2008. This change is not due to differences in administrative coding or a differential application of the algorithm to the study and comparison groups because the administrative databases and their coding did not change from 2006 to 2008. This change is likely due to changes in ICD-9 codes for diagnoses introduced after 2006, some of which we were able to account for through updates to the code, conducted in collaboration with the Massachusetts Division of Health Care Finance and Policy. On inspection, these appear to represent a large variety of codes, many of which would be indeterminate or high severity.
It is also possible that there are confounding effects caused by the deterioration in the US economy in 2008. However, because the recession officially began on October 1, 2008, we expect a marginal influence during the earlier part of 2008.
In this study, we evaluated the extent to which Massachusetts health reform led to changes in utilization of the ED, in particular, for conditions that could potentially be treated outside the ED setting. Our study has several notable findings. First, consistent with national trends, overall ED utilization continued to increase during the study period despite the reduction in the number of uninsured. The 4.1% increase in ED visits in our hospitals was comparable to the 4.6% increase in visits statewide according to data from the Massachusetts Division of Health Care Finance and Policy.
These results suggest that health reform is not likely to lead to an overall decrease in ED visits. The rate of increase in ED visits was less from 2007 to 2008 than it was from 2006 to 2007. Although this may be an indication of the effect of health reform after the individual mandate was instated, ED visit volume in Massachusetts during the past decade can fluctuate from one year to the next,
so longer-term studies will be needed to determine whether health reform has produced any attenuation to the increase in ED visit volume.
Second, although ED visits overall increased during this period, we found a decrease in low-severity ED visits in the group most likely to have been affected by health reform relative to a comparison group. However, the absolute changes were modest. Our methodology is limited by not being able to completely prevent crossover of patients from our study and comparison groups, and as discussed in the “Limitations” section, it is possible that most or all of this finding could be accounted for by the increase in the unclassified category from 2006 to 2008. Nevertheless, to the extent that policymakers expected a substantial decrease in overall and low-severity ED visits, this study does not support those expectations. Finally, overall visits for ambulatory care sensitive conditions in the publicly subsidized/uninsured group decreased by 0.6%, a small change consistent with the modest decrease in low-severity visits. In contrast, the number of hospitalizations for ambulatory care sensitive conditions in this group shows a substantial increase, which seems at odds with the other results and could imply that patients are sicker even within each “severity” class or perhaps that insured patients are more likely to be admitted from the ED.
There are several reasons why the effect of health reform on ED utilization might have been limited. First, although access to health care should be improved when insurance is acquired, limitations in the availability of primary care in Massachusetts might have limited the effect.
In addition, even with adequate coverage, it might take time and effort to alter care-seeking patterns that have become ingrained in some communities. Many of these patients had never had insurance before, so they may have been used to relying on the ED instead of other care settings. In addition, although the Commonwealth Choice private health plans require copayments in the range of $75 to $150 for ED visits, such copayments are low or nonexistent in Medicaid and Commonwealth Care,
which accounted for the largest proportion of insurance expansion under health reform. Although we would expect that high ED copayments would affect this behavior, such a change might require additional time for enrollees to experience these high copayments.
Finally, even before health reform, the rate of uninsurance in Massachusetts was relatively low and many who lacked insurance received free care through the state's uncompensated care pool, thus affording them access to care.
The results of this study are pertinent in addressing the common perception that the nation's uninsured are flooding EDs.
observed that ED visits increased by 28% between 1992 and 2005, but the percentage of uninsured patients remained stable, suggesting that the uninsured are not responsible for increased ED utilization. Newton et al
reviewed the assumptions and evidence concerning adult uninsured patients presenting to the ED and concluded that many of the common assumptions about uninsured patients and their use of the ED and their contribution to ED crowding were observed equally with insured patients. Our findings that overall ED visits continue to increase and that low-severity ED visits decrease only modestly despite a dramatic reduction in the number of uninsured is consistent with results of this previous research and should dispel some of these assumptions.
Previous studies on the specific effect of health insurance on ED utilization have been inconclusive and suggest that other factors such as access to primary care may be more important determinants of ED use.
The landmark RAND Health Insurance Experiment found that insurance with no cost-sharing requirements resulted in significantly higher ED use than insurance with cost-sharing requirements, with a more pronounced effect of reducing “less urgent” ED visits.
found that cutbacks in Oregon's Medicaid program resulted in a sustained increase in ED volume from 2002 to 2004, suggesting that the loss of health insurance could leave the ED as one's main source of care. Finally, one recent population-based study comparing ED utilization between the United States and Ontario, Canada, demonstrated similar visit rates and patterns in these 2 populations, suggesting that health insurance coverage may not have the substantial influence on the overall utilization of emergency care that is hoped for.
Our combined findings from Massachusetts—that the rate of low-severity visits in the study group decreased by only 2.6% and that visits for ambulatory care sensitive conditions decreased by only 0.6%—suggests that other factors play a role in determining access to care and use of the ED in addition to one's insurance status. These likely include availability of primary care, convenience of ED hours, the ability to obtain a comprehensive evaluation and testing at one time in the ED, cultural views about seeking care through primary care or the ED, patient perceptions of severity of illness, and financial factors, including the presence or absence of copayments for ED care. The modest decrease in low-severity and ambulatory care sensitive visits does suggest that access to primary care in Massachusetts continues to be limited. That low-severity visits showed any decrease is a significant finding, but this result is limited by the increase in unclassified visits, and in terms of policy significance we would have expected a more substantial decrease if access to care were dependent only on insurance status.
In conclusion, our findings suggest that access to health insurance is not akin to access to primary or preventive care and likely has a limited, albeit significant, role in affecting ED utilization. Ongoing health care reform efforts should be mindful of this fact. Sufficient attention will need to be paid to the adequacy of the primary care safety net and the myriad other factors contributing to an individual's decision to seek care in an ED.
Glossary of health insurance programs relevant to Massachusetts health reform.
MassHealth: Massachusetts' Medicaid program. Accounts for approximately 120,000 newly insured after health reform.
Commonwealth Care: A subsidized program for low-income adults who are not offered employer-sponsored insurance and do not qualify for Medicare or Medicaid. Covers individuals making up to 300% of the federal poverty level. Accounts for approximately 180,000 newly insured individuals.
Commonwealth Choice: Unsubsidized private insurance for individuals, families, and certain employers. Available from a choice of 6 private health plans through the Commonwealth Health Connector. Accounts for approximately 36,000 newly insured individuals.
Health safety net fund: formerly known as the uncompensated care pool. Provides services for residents with incomes below 400% of federal poverty level and who are not eligible for MassHealth or Commonwealth Care.
The Billings and modified ED severity algorithms.
The initial intent of the Billings ED algorithm was to provide a potentially powerful tool for tracking the characteristics of ED utilization patterns and consequently to what extent ED utilization would be subject to timely and effective primary care both in terms of financial resources (ie, health insurance coverage) and availability of primary care.
in 2007. The algorithm uses ICD-9 diagnosis codes to determine the probability that a given ED visit falls into one of 4 categories: “nonemergency” (NE), “emergency, primary care treatable” (EPCT), “ED care needed, preventable/avoidable” (EDCNPA), and “ED care needed, not preventable or avoidable” (EDCNNPA). Certain diagnoses are not captured in this algorithm and are categorized as unclassified. The original algorithm and its modification are illustrated in Figure 2.
Since the creation of the Billings algorithm, there has been no update to account for newly introduced ICD-9 codes. In our study, with assistance from the Massachusetts Division of Health Care Finance and policy,
Please see page 226 for the Editor's Capsule Summary of this article.
Supervising editor: Donald M. Yealy, MD
Author contributions: PBS, RL, JFW, CWB, SGW, JDS, SWL, and BEL conceived and designed the study. PBS, SGW, LB, CWB, MEM, AS, MCB, and JHP undertook recruitment of participating centers and data collection. PBS, RL, LA, SGW, LB, CWB, JDS, SWL, and BL managed the data, including quality control. PBS, RL, JFW, and BEL provided statistical advice on study design and analyzed the data. PBS drafted the article, and all authors contributed substantially to its revision. PBS takes responsibility for the paper as a whole.
Funding and support: By Annals policy, all authors are required to disclose any and all commercial, financial, and other relationships in any way related to the subject of this article as per ICMJE conflict of interest guidelines (see www.icmje.org). The authors have stated that no such relationships exist.