Abstract
Background
The lung allocation score (LAS) is a tool used to prioritize patients for lung transplantation. For patients with interstitial lung diseases (ILDs), spirometry data are used for the LAS calculation. Spirometry values such as a FVC are subjected to race-specific equations that determine expected values. The effect of race-specific equations in LAS score remains unknown.
Research Question
Did the use of a race-based spirometry equation lead to longer waitlist times for Black patients?
Study Design and Methods
We performed a retrospective analysis of patients listed for lung transplantation from 2005 through 2020 using publicly available data from the United Network for Organ Sharing. We recalculated LAS scores for Black patients using White-specific equations with the available variables. The primary objective was to evaluate the effect of race-specific equations on LAS scores and time on the transplant waitlist.
Results
A total of 33,845 patients listed for lung transplantation were included in the analysis. White patients were listed at lower LAS scores, a higher proportion of White patients underwent transplantation, and White patients died on the waitlist at lower rates. When recalculating LAS scores using White-specific equations, Black patients with ILD had up to a 1.9-point higher score, which resulted in additional waitlist time.
Interpretation
Race-specific equations led to longer wait times in Black patients listed for lung transplantation. The use of race-based equations widened already known disparities in pulmonary transplantation.
Key Words: disparities, spirometry, transplant
Graphical Abstract
Take-home Points.
Study Question: Did the use of race-based spirometry equations lead to longer waitlist times for Black patients awaiting lung transplantation?
Results: When recalculating lung allocation scores using White-specific equations, Black patients with interstitial lung disease had up to a 1.9-point higher score, which resulted in additional waitlist time.
Interpretation: Race-specific equations led to longer wait times for Black patients listed for lung transplantation.
Before 2021, racially adjusted pulmonary function test (PFT) findings played an important role in determining transplant priority for tens of thousands of patients listed for lung transplantation. Before listing, each individual considered or listed for lung transplantation underwent a series of tests and procedures to determine the lung allocation score (LAS) and therefore the transplant priority.1 The LAS was calculated differently depending on the underlying lung disease process. To calculate the LAS for individuals with interstitial or restrictive lung diseases, the patient’s FVC was compared with a predicted value determined by the person’s age, sex, height, and self-identified race to determine the percentage of the predicted value.2,3 If all other inputs were the same, a person who identified as White would have had a higher predicted FVC than an individual identifying as any other race.4,5 Therefore, if a White patient and a patient from another race had the same measured FVC value, the White patient would have had a lower FVC % predicted, translating to a higher LAS and increased transplant priority. In March 2023, the lung transplant community transitioned from the LAS to the composite allocation score (CAS) to mitigate disparities related to blood type, height, race, sex, and geographic location.6 This transition to the CAS is expected to reduce deaths of those on the waitlist and to decrease sex disparities, although its effect on mitigating social factors remains unknown.7
The greater medical community recently turned a critical eye to the use of a patient’s racial self-identity to allocate treatments or make diagnostic decisions. Racial self-identity can be fluid throughout an individual’s life and, although it may overlap with genetic ancestry, it is not a biological determinant, but rather a social construct.8 Additionally, using race in predicting PFT values is the result of historical attempts to support the enslavement of human beings further based on racial identification.9 Prior studies that blurred the lines between genetic ancestry and racial self-identity found significant associations between genetic markers they associated with non-European ancestry (and therefore non-White races) and lung function. In addition, ancestry is linked to oppressive social circumstances.8, 9, 10, 11 However, these studies, along with many others, also have acknowledged that lung function in adults also is dependent on a number of environmental exposures in the prenatal period and during childhood that typically are more common among individuals from racial and ethnic minority groups.5,10, 11, 12, 13 This in turn may normalize lower lung function in these groups, which might not exist had they not been exposed to such disparities. As a result, pulmonary professional societies recently called for eliminating the use of race from predictive spirometry equations.14,15 However, this practice may have come too late for some patients for whom racial-specific spirometry equations were used to make transplantation decisions, transposing society’s racial disparities directly onto the bodies of patients.
To quantify the impact that the race-specific equations for predicted spirometry values had on the LAS and time spent on the lung transplant waiting list, we conducted a retrospective analysis of all individuals listed for lung transplantation in the United States from 2005 through 2020. We sought to recalculate LASs for Black patients, the patients who have the lowest predicted FVC values using widely available equations, to quantify the group experiencing the greatest harm from this practice. Additionally, Black patients have been the only racial group consistently differentiated from White patients in the two lung function predictive equations that have been used widely over the past 20 years (the National Health and Nutrition Examination Survey and the Global Lung Function Initiative [GLI]). It is important to note that FVC % predicted values are no longer part of any scoring system for lung transplantation. To our knowledge, this is the first study to quantify this historical effect and therefore to expand our collective understanding of disparities in transplantation allocation and chronic lung disease management in the United States.
Study Design and Methods
We obtained publicly available datasets from the United Network for Organ Sharing (UNOS) for this analysis; specifically, we used data from the files named THORACIC_DATA and THORACIC_LAS_HISTORY_DATA. We included patients who were aged 18 years or older and were listed for lung transplantation from June 1, 2005, through December 30, 2020. We excluded patients younger than 18 years at the time of listing, those listed for retransplantation, and those listed for combined solid organ transplantation. We evaluated data available for only the first lung transplant listing for patients with multiple listings. This study was evaluated by the institutional review board of the University of Colorado and found to be exempt given the use of a publicly available de-identified data set.
To evaluate baseline differences, the characteristics of the five racial and ethnic groups provided in the UNOS data set (non-Hispanic/Latinx White/Caucasian, non-Hispanic/Latinx Black/African American, Hispanic/Latinx, Asian, and other) were assessed. Baseline information included demographic (eg, age, sex) and clinical (disease severity measured by LAS at the time of listing) characteristics.
The primary objectives of the study were to investigate the change in LAS when race-specific equations for FVC were modified and to simulate the effect on waitlist time. To this end, we recalculated individual LAS based on the publicly available formula16 and changed the FVC % predicted for Black patients based on White-specific equations for the GLI and the Third National Health and Nutrition Examination Survey (NHANES III) correction (e-Table 1). We used both GLI and NHANES III because they were the equations used during the study period and the data obtained do not distinguish which equation was used at the time of LAS calculation. We chose to recalculate all LAS for Black patients as if they had been White patients to capture the largest potential difference in LAS based on racial identity alone. We anticipate that recalculating scores using other possible racial identification or race-neutral categories (eg, GLI-Other or GLI-Global) would produce smaller differences. Additionally, many patients were listed before the creation of GLI and the new GLI-Global algorithm, and therefore using these scores as comparisons would underestimate real delays experienced by these patients based on their racial identity. Although the initial LASs provided to UNOS were included in the data set for each patient, we needed to recalculate an initial score for each patient so that we then could modify a single value (FVC) to recalculate a new score. For the recalculated score, we used the earliest possible score, but if a variable was not available at that time, then the next available value at a later time point was used. Therefore, all patients had an initial LAS and a recalculated initial LAS. Although only patients in group D (restrictive lung diseases) had an FVC % predicted as part of the LAS formula, we wanted to assess the effect on the entire Black population listed for transplantation so that all eligible patients were included in the analysis. Furthermore, given that most patients are listed at an LAS of approximately 35 to 45 (Table 1), we performed subgroup analyses in the cohort of patients with initial scores in this range. We performed additional subgroup analysis among those with restrictive lung disease (group D) because the LAS only for patients in this group included FVC % predicted. Finally, the change in wait time based on a single-point change in LAS was assessed using the entire cohort to model and describe subgroups to determine the effect of changes in LAS on waitlist time.
Table 1.
Baseline Characteristics of the Study Population: Patients Listed for Lung Transplantation 2005-2020
| Characteristic | Patients Listed for Transplantation (N = 33,845) |
|---|---|
| Age, y | 56.2 ± 12.7 |
| Male sex | 19,182 (56.7) |
| Race | |
| White, non-Hispanic/Latinx | 27,003 (79.8) |
| Black, non-Hispanic/Latinx | 3,247 (9.6) |
| Hispanic/Latinx | 2,607 (7.7) |
| Asian | 740 (2.2) |
| American Indian/Alaska Native | 119 (0.4) |
| Native Hawaiian/Pacific Islander | 29 (0.1) |
| Multiracial | 100 (0.3) |
| Initial LAS | 37.1 (33.4-44.5) |
Data are presented as No. (%), mean ± SD, or median (interquartile range). LAS = lung allocation score.
Statistical Analysis
Categorical variables were reported as proportions and continuous variables were reported as mean ± SD or median (interquartile range). To analyze normally distributed and nonnormally distributed data, t tests and Mann-Whitney U tests, respectively, were used. Categorical variables were analyzed using Fisher exact test. A P value of .05 was deemed statistically significant.
A mixed-effect linear regression was used to test the hypothesis that initial LAS predicted total time on the waitlist for lung transplantation among those who had undergone transplantation successfully. A mixed-effect model was chosen with the initial LAS, patient height (in centimeters), patient race or ethnicity, and blood type as fixed effects and transplant center volume as a random effect. LAS, patient height, and transplant center volume were treated as continuous variables, whereas blood type and race or ethnicity were treated as factor (categorical) variables. Fixed-effect factors were selected for inclusion that were identified in the Organ Procurement & Transplantation Network/Scientific Registry of Transplan Recipients 2020 annual report as being associated significantly with transplantation.1 This was the final annual report of transplantations allocated by LAS. Transplant center volume was assigned for each patient based on the total number of lung transplants performed at their assigned transplant center during the year before the transplantation. Because waitlist time was evaluated among patients who underwent transplant data structure, the fact that data availability would be associated with transplant center volume was accounted for by treating center volume as a random effect. Because transplant center volume was used as the random effect and not transplant center identity, and therefore multiple centers theoretically could be grouped together when evaluating the random effect, an independent model of covariance was chosen that did not account for repeated measures within the random effect groupings. To account for patients who had died or been delisted, the same regression model was used separately to evaluate the entire cohort of patients who had been listed and received an initial LAS, regardless of waitlist outcome, with either transplant, delisting, or death as a censoring event. The data were analyzed using STATA version 17 software (StataCorp).
Results
From 2005 through 2020, 38,817 patients were listed for lung transplantation. Of those, 1,350 were excluded because they were younger than 18 years at the time of listing and 2,943 were excluded because they were listed as a retransplantation or a multiorgan transplantation. An additional 679 patients were excluded because they lacked one or more data values required to recalculate the LAS (Fig 1). Of the 33,845 included patients, the mean age was 56.2 years, 27,003 patients (79.8%) were White, 19,182 patients (56.7%) were male, and the median LAS at the time of listing was 37.1 (Table 1). The racial and ethnic breakdown of patients with group D diagnosis (restrictive lung disease) was similar to that of the entire cohort (Table 2). Black, Hispanic or Latinx, and Native American patients were significantly younger than non-Hispanic or Latinx White patients at the time of transplantation listing. All racial and ethnic groups, except those who identified as multiracial, had higher mean LASs compared with non-Hispanic or Latinx White patients at the time of listing (Table 3). Black, Hispanic or Latinx, and Asian patients were significantly less likely to receive transplants, after being listed, than White patients. The mean time on the waitlist before transplantation was 147.1 days. Despite younger age and higher initial listing LAS among Black and Hispanic or Latinx patients (43.3 and 47.4, respectively, vs 40.6 for non-Hispanic or Latinx White patients), wait time for transplantation was the same when comparing all ethnic groups with White patients except for patients who identified as multiracial, who waited longer (Table 3).
Figure 1.
Flow chart showing disposition of the 38,817 patients who were listed for lung transplantation from 2005 through 2020.
Table 2.
Racial and Ethnic Breakdown of Patients Listed With a Group D Diagnosis
| Variable | Patients Listed With a Group D Diagnosis (n = 21,071) |
|---|---|
| White, non-Hispanic/Latinx | 15,444 (73.3) |
| Black/African American | 2,484 (11.8) |
| Hispanic/Latinx | 2,278 (10.8) |
| Asian | 682 (3.2) |
| Native American/Alaska Native | 98 (0.50) |
| Native Hawaiian/Pacific Islander | 23 (0.11) |
| Multiracial | 62 (0.30) |
Data are presented as No. (%).
Table 3.
Listing Characteristics and Outcomes by Race and Ethnicity
| Variable | Age at Time of Listing, y | P Value | LAS at the Time of Listing | P Value | No. of Patients Transplanted | P Value | Time on Waitlist, d | P Value | Patients Who Died While on Waitlist | P Value | Time on Waitlist for Transplanted |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Total population (N = 33,845) | 56.2 ± 12.7 | …a | 41.5 ± 16.5 | …a | 26,726 (79.0) | …a | 147.1 ± 380.9 | …a | 7,119 | …a | 105.4 ± 3.3 |
| Initial scores 35-45 (n = 13,177) | 54.9 ± 13.9 | …a | 38.9 ± 2.8 | …a | 10,765 (81.7) | …a | 114.8 ± 323.7 | …a | 2,412 (18.3) | …a | 47.0 ± 3.0 |
| White, non-Hispanic/Latinx (n = 27,003) | 56.8 ± 12.8 | Reference | 40.6 ± 16.2 | Reference | 21,666 (80.2) | Reference | 142.2 ± 248.9 | Reference | 5,337 (19.8) | …a | 93.0 ± 3.4 |
| Black/African American, non-Hispanic/Latinx (n = 3,247) | 53.0 ± 11.0 | < .001 | 43.3 ± 16.7 | < .001 | 2,437 (75.1) | < .001 | 151.1 ± 252.6 | .09 | 810 (24.9) | < .001 | 118.2 ± 10.5 |
| Hispanic/Latinx (n = 2,607) | 54.0 ± 13.1 | < .001 | 47.4 ± 17.9 | < .001 | 1,922 (73.7) | < .001 | 135.2 ± 234.8 | .21 | 685 (26.3) | < .001 | 191.1 ± 16.1 |
| Asian (n = 740) | 56.0 ± 12.7 | .06 | 47.5 ± 17.6 | < .001 | 508 (68.6) | < .001 | 130.5 ± 232.3 | .28 | 232 (31.4) | < .001 | 234.6 ± 43.9 |
| Native American/Alaska Native (n = 119) | 54.3 ± 11.7 | .03 | 44.2 ± 15.9 | .01 | 89 (74.8) | .14 | 148.6 ± 154.3 | .81 | 30 (26.3) | .14 | 216.5 ± 136.6 |
| Native Hawaiian/ Pacific Islander (n = 29) | 55.9 ± 8.9 | .69 | 47.0 ± 17.3 | .03 | 21 (72.4) | .29 | 123.0 ± 205.3 | .72 | 8 (27.6) | .29 | 81.2 ± 23.0 |
| Multiracial (n = 100) | 53.3 ± 13.3 | .008 | 40.4 ± 14.5 | .87 | 83 (83) | .46 | 200.9 ± 372.9 | .03 | 17 (17) | .49 | 79.8 ± 34.9 |
Data are presented as No. (%) or mean ± SD, unless otherwise indicated. LAS = lung allocation score.
No comparisons made for the Total population and Initial scores rows.
Initial LASs were recalculated for all patients using the provided FVC % predicted values and granular data available from UNOS. The mean ± SD recalculated score was 50.0 ± 17.0, an increase of 8.5 points over the initial score reported to UNOS. This difference varied by ethnic group (e-Table 2). The mean ± SD recalculated score among all listed Black patients was 52.5 ± 17.4. This score increased by 1.1 points and 1.3 points when equations for White patients based on GLI and NHANES III, respectively, were used. Among Black patients with an initial LAS reported to UNOS of between 35 and 45 (mean, 39.1), the mean recalculated score was 48.1 and the score increases were 1.4 and 1.6 by GLI and NHANES III scores, respectively. Among those with a group D listing diagnosis, the mean recalculated initial LAS was 55.7 and increased by 1.4 and 1.7 points by GLI and NHANES III scores, respectively. Among those with a group D listing diagnosis and an initial listing score reported to UNOS of between 35 and 45, the mean recalculated score was 48.8, increasing by 1.6 and 1.9 points by GLI and NHANES III scores, respectively (Table 4).
Table 4.
LAS Change for Black or African American Patients When Using NHANES III and GLI Equations for White Patients
| Variable | Recalculated Initial Reported LAS |
Mean Change |
||||
|---|---|---|---|---|---|---|
| Overall | Including NHANES III Race Correction | Without Race Correction (GLI) | Without Race Correction (NHANES III) | GLI | NHANES III | |
| All (n = 3,247) | 43.3 ± 16.7 | 52.5 ± 17.4 | 53.7 ± 17.6 | 53.8 ± 17.6 | 1.1 ± 1.0 | 1.3 ± 1.2 |
| Initial LAS of 35-45 (n = 1,357) | 39.1 ± 2.8 | 48.1 ± 11.0 | 49.6 ± 11.3 | 49.7 ± 11.3 | 1.4 ± 0.9 | 1.6 ± 1.1 |
| ILD (n = 2,484) | 45.5 ± 17.2 | 55.7 ± 17.4 | 57.3 ± 17.4 | 57.4 ± 17.4 | 1.4 ± 0.9 | 1.7 ± 1.1 |
| ILD and initial LAS of 35-45 (n = 1,160) | 39.2 ± 2.8 | 48.8 ± 11.1 | 50.5 ± 11.3 | 50.6 ± 11.4 | 1.6 ± 0.7 | 1.9 ± 0.9 |
Data are presented as mean ± SD. GLI = Global Lung Function Initiative; ILD = interstitial lung disease; LAS = lung allocation score; NHANES III = Third National Health and Nutrition Examination Survey.
The mixed-effect regression model found that an average increase of 1 point of initial LAS reported in UNOS led to a decrease of 3.2 days (95% CI, 3.0-3.4 days) on the waiting list among all patients who received a transplant and a decrease of 9.5 days (95% CI, 8.3-10.7 days) among those with initial scores between 35 and 45. Based on this, Black patients who ultimately received a transplantation faced an additional 3.5 days on the waitlist on average regardless of initial LAS and an additional 18.1 days for those in the high-priority transplant group with initial scores of between 35 and 45. This increase in days on the waitlist represents a wait time that overall was 4% longer compared with that of White counterparts with the same FVC value and other LAS components and 21% longer for those with initial LASs between 35 and 45 (Table 5).
Table 5.
Mixed-Effect Linear Regression Evaluating Change in Waitlist Time per LAS
| Initial LAS Range | Change in Waitlist Time, d | 95% CI |
|---|---|---|
| All, transplanted (n = 27,209) | 3.2 | 3.0-3.4 |
| 35-45, transplanted (10,945) | 9.5 | 8.3-10.7 |
| All, including deceased and delisted (n = 33,618) | 4.4 | 4.2-4.6 |
| 35-45, including deceased and delisted (n = 13,036) | 11.6 | 10.2-12.9 |
LAS = lung allocation score.
Discussion
In this cohort of patients listed for lung transplantation in the United States between 2005 and 2020, Black patients with ILD were listed for transplantation at higher initial LASs (43.3 vs 40.6 for White patients), despite their scores being decreased artificially because of race-correcting equations. These patients with initial scores in the clinically relevant range of between 35 and 45 would have seen the LAS decreased by approximately 1.6 or 1.9 points based on the choice of predictive reference equation (GLI or NHANES III, respectively), likely increasing the wait time by as much as 19.1%. Therefore, the use of race-specific equations led to significantly longer waitlist times for a group of patients who already faced inequities in the listing process.
These findings must be considered in the general context of lung transplantation disparities. Our analysis of the data supports previous findings that Black patients were less likely to receive a lung transplantation and experienced similar waiting times for transplantation as White patients, despite higher LAS at the time of listing and younger age at the time of listing.17 Although it is possible that this may be the result of differences in listing diagnosis, this disparity in organ allocation may be explained partially by the finding that race correction significantly decreases initial LAS for Black candidates. In addition, the use of race-based equations also might have an impact on referral to a lung transplantation center given guideline-related thresholds for referral. Our findings suggest that race-specific predicted equations for PFT, which underestimate the severity of lung disease in Black patients, added to an already inequitable field in lung transplantation allocation. Previous studies have demonstrated that non-White candidates have lower access to lung transplantation and were listed as having higher disease severity and younger ages.3,17 Interestingly, among those who lived to transplantation despite this disparity, outcomes after transplantation were similar among White and non-White patients.18
Other areas of medicine have begun examining the effects of integrating racial correction into the physiologic measurements used to determine organ allocation. A study examining the role of racial correction in kidney transplantation found that removing the use of racial correction likely would increase access to specialists, nutrition therapy, renal disease education, and renal transplantation.19 In pulmonary medicine, the effect of race-specific spirometry equations on clinical outcomes remains unknown, but recent work suggests that Black patients may be less likely to receive a diagnosis of preserved ratio impaired spirometry and occupational lung disease.20,21 Moreover, given the reliance on FVC for diagnosis of ILD, it is plausible that disease in Black patients is being underdiagnosed, and therefore proper management is delayed. In addition, our results similarly suggest that unfounded race-based equations impacted organ allocation for a group of patients who already face barriers to life saving lung transplantation. More recently, the American Thoracic Society released a statement, endorsed by the European Respiratory Society, that advocated for the removal of race and ethnicity from pulmonary function test interpretation.20 Despite this recent statement, it is important to understand the historical harms that the use of race and ethnicity as biological variables have inflicted on historically marginalized communities.
The strength of this study is that it is comprehensive, including all patients in the United States who were listed for lung transplantation over a broad range of time using publicly available data and formulas. Our study was limited by the fact that the LASs were recalculated using variables that might have been collected at different time points. This was true for all patients included, but this was unavoidable given the nature of the data that are available for use. Furthermore, we attempted to recalculate the score by assigning default values to missing variables or by removing patients who did not have all variables at the earliest time point, which both yielded more discrepant scores when compared with the reported LAS at the time of listing. Another limitation is that for a number of patients, LAS exemptions are made that aim at advocating for higher scores. Previous data demonstrate that, from 2006 through 2014, a lung review board request was made for only 3.4% of all candidates, which is unlikely to change the conclusions of our study.22 That being said, the increase in LAS associated with changes in race reflects an important disparity that affected Black patients and led to unnecessary harm. It is worth noting that currently, LAS calculation does not include the use of FVC, but understanding the historical implications of race-based values remains critically important to avoid further harm to patients from minority populations.
Addressing the use of race in PFT results is important for several reasons. First and foremost, race is a social construct and not a biological one.15 Previous studies that reported differences between Black and White lungs failed to recognize the importance of socioeconomic factors in lung health. For example, Rossiter and Weill10 found that Black individuals had a 13.2% lower total lung capacity when compared with White people, but they failed to account for socioeconomic factors because these were thought to be “unimportant.”21 Furthermore, it was reported previously that the differences in adult lung function are related to differences in peak function (because trajectories in the decline of lung function in Black and White patients seem to be similar), suggesting that impaired lung growth during childhood represents a major factor.5,21 Previous studies also have compared lung function across different populations in Africa and have found discrepancies when compared with that of Black Americans, suggesting the lack of biological basis for the concept of the Black lung.21 Second, the concept of self-identified race often is complex and nuanced. With a growing number of individuals identifying as multiracial and multiethnic and significant differences in the proportion of African ancestry among Black individuals, the use of race as a category for biological purposes seems to be obsolete.23 Third, the use of pulmonary function testing goes beyond transplant evaluation. Although, since late 2021, spirometry is no longer part of the LAS calculation, PFT findings are crucial in the diagnosis and management of a myriad of pulmonary diseases, including cystic fibrosis, COPD, asthma, idiopathic pulmonary fibrosis, and others. Furthermore, in an ever-changing field, it is conceivable that spirometric data might be considered in future iterations of allocation scores. In summary, assuming that the harm of race-specific equations for spirometry was limited only to transplant prioritization is incorrect. Therefore, our data further support the recent recommendations by the American Thoracic Society and European Respiratory Society.
Interpretation
Black and other non-White patients already are listed at higher LAS, suggesting bias in the timing of the decision to list for transplantation. The previous use of race-specific spirometry equations led to further unnecessary and avoidable delays in transplantation among Black and other non-White patients that ultimately may explain why fewer non-White patients receive lung transplants after being listed. Now that the LAS is no longer used and spirometry values are not part of the CAS, it is important to evaluate the effect of CAS in racial and ethnic disparities in lung transplantation. Broadly, identifying sources of systematic racial bias in medicine is crucial to reduce racial disparities in medicine. One step toward reducing racial disparities in patients with lung disease should include the promoting the adoption of the recent society guideline regarding the elimination of race-specific equations for PFT results.
Funding/Support
This study was funded by the National Institutes of Health (Grant 1F32HL167572-01A1K to D. C. H. and grant 1R01NR020470-01A1 to K. R.).
Financial/Nonfinancial Disclosures
None declared.
Acknowledgments
Author contributions: D. C. H. and M. G. had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis, inculding and specially any adverse effects. D. C. H. served as principal author. K. J. R., E. A. H., F. H., E. F., and D. J. W. contributed substantially to the study design, data analysis and interpretation, and the writing of the manuscript.
Disclaimer: The views expressed in this article are the authors and do not necessarily reflect the positions or policies of the Department of Veterans Affairs or the United States government.
Role of sponsors: The sponsor had no role in the design of the study, the collection and analysis of the data, or the preparation of the manuscript.
Additional information: The e-Tables are available online under “Supplemental Data.”
Supplementary Data
References
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