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Socioeconomics
Original research
Racial and insurance based disparities in the treatment of carotid artery stenosis: a study of the Nationwide Inpatient Sample
  1. Waleed Brinjikji1,
  2. Abdulrahman M El-Sayed1,
  3. David F Kallmes2,
  4. Giuseppe Lanzino1,3,
  5. Harry J Cloft1,3
  1. 1Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
  2. 2Department of Epidemiology, Columbia University, New York, New York, USA
  3. 3Department of Neurosurgery, Mayo Clinic, Rochester, Minnesota, USA
  1. Correspondence to Dr W Brinjikji, Department of Radiology, Mayo Clinic, 200 SW First Street, Rochester, MN 55905, USA; brinjikji.waleed{at}mayo.edu

Abstract

Background and purpose Minorities and uninsured/underinsured patients have poorer access to healthcare system resources, especially preventative treatments. We sought to determine whether racial and insurance based disparities existed in the treatment of carotid artery stenosis.

Methods Using the Nationwide Inpatient Sample, hospitalizations for carotid artery stenting and carotid endarterectomy for symptomatic and asymptomatic carotid artery stenosis from 2005 to 2011 were identified. We calculated χ2 tests, and bivariate and multivariable logistic regression models were fit to assess differences in the characteristics of patients receiving carotid revascularization for asymptomatic compared with symptomatic carotid artery stenosis. Demographic characteristics studied included race/ethnicity (white, black, Hispanic, Asian/Pacific Islander) and primary payer status (Medicare, Medicaid, private insurance, self-pay and no charge).

Results Between 2005 and 2011, 890 680 patients underwent carotid revascularization for the treatment of carotid artery stenosis (92.1% asymptomatic and 7.9% symptomatic). Multivariate logistic regression analysis demonstrated that Medicaid (OR=0.87, 95% CI 0.83 to 0.92, p<0.0001) and self-pay patients (OR=0.48, 95% CI 0.45 to 0.51, p<0.0001) had a lower odds of being revascularized for asymptomatic carotid artery stenosis compared with private insurance patients. Black (OR=0.81, 95% CI −0.77 to 0.84, p<0.0001) and Hispanic (OR=0.86, 95% CI −0.83 to 0.90, p<0.0001) patients had significantly lower odds of revascularization for asymptomatic carotid artery stenosis compared with white patients.

Conclusions Minorities and self-pay/Medicaid patients were less likely to receive carotid revascularization when asymptomatic—rather they were more likely to have treatment only after symptoms had developed. These findings suggest possible disparities in the degree of morbidity related to carotid artery stenosis, the likelihood of early detection, and/or the likelihood of treatment conditional on indication.

  • Stent
  • Economics
  • Stroke

https://doi.org/10.1136/neurintsurg-2014-011294

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    Introduction

    Previous studies have demonstrated significant socioeconomic disparities in access to healthcare system resources, especially preventative treatments.1–6 In the setting of both symptomatic and asymptomatic carotid artery stenosis, prior studies have demonstrated that carotid revascularization decreases the risk of future stroke in select patients.7–11 However, little is known about differences in rates of carotid revascularization in the treatment of carotid artery stenosis by race/ethnicity and/or insurance status.

    Carotid artery stenosis treatment is unique as there are two mutually exclusive indications for carotid revascularization representing treatment at different points in the natural history of the disease. Revascularization procedures may be recommended for asymptomatic patients with stenosis >60%, or for symptomatic patients with stenosis >50%. In this respect, comparing the demographic characteristics of symptomatic and asymptomatic carotid artery stenosis patients receiving revascularization represents a unique opportunity to assess racial and insurance based disparities in the treatment of carotid artery stenosis, as those receiving treatment for symptomatic stenosis do not, by definition, receive surgical treatment for asymptomatic stenosis and thus are treated following progression of asymptomatic disease to symptomatic disease.9–12

    Using the Nationwide Inpatient Sample (NIS) 2005–2011, we compared racial/ethnic and insurance characteristics of patients undergoing carotid revascularization for asymptomatic versus symptomatic carotid artery stenosis. We hypothesized that there would be a higher ratio of racial minorities and uninsured patients in the symptomatic group due to less diagnosis and treatment, both medical and surgical, of asymptomatic carotid stenosis.

    Methods

    Patient population

    We purchased the NIS hospital discharge database for the period 2005–2011 from the Healthcare Cost and Utilization Project of the Agency for Healthcare Research and Quality (Rockville, Maryland, USA). The NIS is a hospital discharge database that includes 20% of all inpatient admissions to non-federal hospitals in the USA. Discharge weights were applied to this study for representativeness.

    We selected all patients receiving carotid endarterectomy (ICD-9 procedure code 3812) and carotid artery stenting (ICD-9 procedure code 0061 and 0063). Patients treated for asymptomatic carotid artery stenosis were identified using ICD-9 diagnosis codes 43310 and 43330. Symptomatic carotid artery stenosis patients were identified using ICD-9 procedure codes 43311 and 43331. Demographic variables collected included race/ethnicity (white, black, Hispanic, Asian/Pacific Islander) and primary payer (Medicare, Medicaid, private insurance, and self-pay). Comorbidities included were smoking, hyperlipidemia, coronary artery disease, hypertension, diabetes, and obesity. Hospital level characteristics included hospital region and hospital location/teaching status. Information as to whether admission was elective was also obtained.

    Variables and outcomes

    Demographic characteristics were compared between the two groups: (1) symptomatic carotid artery stenosis and (2) asymptomatic carotid artery stenosis. An underlying assumption of our analysis is that symptomatic patients will necessarily present to hospitals and providers, and receive appropriate treatment for their disease, while asymptomatic patients will typically be treated on an elective basis and demographic factors might impact on the tendency of patients to seek medical care and how medical care is delivered. Based on this assumption, the demographics of symptomatic disease are treated as a control group, representative of overall carotid artery stenosis demographics. After this assumption, demographic differences in the asymptomatic relative to the symptomatic group are likely secondary to differences in the tendency of patients to seek medical care and how medical care is delivered.

    For each group, demographic information analyzed included age, race/ethnicity (white, black, Hispanic, Asian/Pacific Islander), sex, primary payer (Medicare, Medicaid, private insurance, self-pay), and Charlson Comorbidity Index. We performed five subgroup analyses.

    1. Comparison of demographics in the asymptomatic and symptomatic groups among patients receiving carotid endarterectomy and carotid artery stenting separately.

    2. We separated the study into two time periods, 2005–2008 and 2009–2011, to determine if demographic differences existed across time periods.

    3. Comparison of demographic differences in the asymptomatic and symptomatic groups among patients aged <65 years and those aged ≥65 years separately, as patients aged ≥65 years generally have access to Medicare. We performed this analysis to determine whether differences in access to insurance affected the demographics of carotid disease treatment.

    4. A subgroup analysis to determine whether any demographic variable was associated with an increased rate of carotid artery stenting versus endarterectomy.

    5. A subgroup analysis to determine whether the racial and insurance based disparities in revascularization for asymptomatic and symptomatic disease are similar across geographic regions in the USA.

    Statistical analysis

    Means are presented with their corresponding SDs; χ2 tests were used to compare categorical variables and the Student's t test was used to compare continuous variables. Reference groups were identified a priori based on our hypothesis that white patients and well insured patients would be more likely to receive carotid revascularization for asymptomatic carotid artery stenosis. For race, the reference group was white patients. For income and insurance status, the reference group was privately insured patients. For univariate analyses, we calculated ORs as a measure of effect size. We fitted two multivariable logistic regression models. For the first model, the outcome was asymptomatic versus symptomatic indications for carotid revascularization, which was regressed on the demographic covariates of interest and adjusted for age, sex, Charlson Comorbidity Index, hospital region, location, and bed size.13 A second multivariable model of carotid stenting was fitted by the demographic covariates of interest and adjusted by age, sex, Charlson Comorbidity Index, hospital region, location, bed size, and indication for treatment (symptomatic vs asymptomatic). All statistical analysis was performed using the SAS based statistical package JMP V.9.0 (http://www.jmp.com).

    Results

    Patient characteristics

    Between 2005 and 2011, 890 680 patients underwent carotid revascularization for the treatment of carotid artery stenosis. The number of patients undergoing revascularization decreased from 132 729 in 2005 to 117 341 in 2011. The decrease was primarily due to a decrease in revascularization for asymptomatic disease, as in 2005, 123 284 patients underwent revascularization for asymptomatic disease compared with 106 884 patients in 2011. The proportion of patients undergoing revascularization for symptomatic disease increased from 7.1% in 2005 to 8.9% in 2011. These findings are summarized in figure 1.

    Figure 1
    Figure 1

    Number of revascularization patients for asymptomatic and symptomatic carotid artery stenosis, 2005–2011.

    A total of 820 432 patients (92.1%) were asymptomatic and 70 248 (7.9%) were symptomatic. We found that 781 608 patients (87.8%) underwent carotid endarterectomy and 109 072 patients (12.2%) underwent carotid artery stenting. White patients numbered 633 462 (90.6%), and 192 811 patients (22.1%) had private insurance. Regarding admissions, 82.1% of admissions (672 120 admissions) for revascularization of asymptomatic disease were elective compared with 37.7% of admissions (26 451 admissions) for symptomatic disease (p<0.0001). These data are summarized in table 1.

    View this table:
    Table 1

    Characteristics of patients undergoing carotid revascularization in the Nationwide Inpatient Sample

    Comparison of demographic group by indication for revascularization

    Compared with symptomatic carotid stenosis patients undergoing carotid revascularization, asymptomatic revascularization patients had a significantly higher mean age (71.1±20.9 vs 69.8±24.1 years; p<0.0001). Compared with white revascularization patients, black revascularization patients (OR=0.72, 95% CI 0.69 to 0.75), Hispanic revascularization patients (OR=0.79, 95% CI 0.76 to 0.82), and Asian revascularization patients (OR=0.81, 95% CI 0.76 to 0.82) were significantly less likely to undergo revascularization for asymptomatic disease. Compared with Medicare revascularization patients, Medicaid revascularization patients (OR=0.60–95% CI 0.58 to 0.64), private insurance revascularization patients (OR=0.78, 95% CI 0.77 to 0.79), and self-pay revascularization patients (OR=0.37, 95% CI 0.28 to 0.46) were significantly less likely to undergo revascularization for asymptomatic disease. These differences were consistent across treatment modalities and time periods. These data are summarized in tables 2 and 3.

    View this table:
    Table 2

    Comparison of demographic characteristics between asymptomatic and symptomatic carotid artery stenosis patients undergoing carotid revascularization procedures in the Nationwide Inpatient Sample

    View this table:
    Table 3

    Comparison of demographic characteristics between asymptomatic and symptomatic carotid artery stenosis patients undergoing carotid revascularization procedures in the Nationwide Inpatient Sample by time period (2005–2008 and 2009–2011)

    Among patients <65 years, 193 761 underwent treatment for asymptomatic disease and 21 571 underwent treatment for symptomatic disease. Similar to the overall cohort, black revascularization patients (OR=0.73, 95% CI 0.69 to 0.78) and Hispanic revascularization patients (OR −0.79, 95% CI 0.74 to 0.85) had significantly lower odds of revascularization for asymptomatic disease than white revascularization patients. Compared with Medicare revascularization patients, Medicaid revascularization patients (OR=0.71, 95% CI 0.67 to 0.75), private insurance revascularization patients (OR=0.88, 95% CI 0.85 to 0.92), and self-pay revascularization patients (OR=0.39, 95% CI 0.37 to 0.42) had significantly lower odds of revascularization for asymptomatic carotid artery stenosis.

    Among patients ≥65 years, 452 777 received treatment for asymptomatic disease and 40 369 received treatment for symptomatic disease. Compared with white revascularization patients, black revascularization patients (OR=0.74, 95% CI 0.71 to 0.78), Hispanic revascularization patients (OR=0.79, 95% CI 0.76 to 0.83), and Asian revascularization patients (OR=0.77, 95% CI 0.70 to 0.84) were significantly less likely to undergo revascularization for asymptomatic carotid artery stenosis. Compared with Medicare revascularization patients, Medicaid revascularization patients (OR=0.63, 95% CI 0.57 to 0.69), private insurance revascularization patients (OR=0.87, 95% CI 0.84 to 0.90), and self-pay revascularization patients (OR=0.66, 95% CI 0.58 to 0.75) were significantly less likely to undergo revascularization for asymptomatic disease. These data are summarized in table 4.

    View this table:
    Table 4

    Comparison of demographic characteristics between asymptomatic and symptomatic carotid artery stenosis patients undergoing carotid revascularization procedures in the Nationwide Inpatient Sample by age group (<65 and ≥65 years)

    Comparison of type of carotid revascularization

    Compared with white revascularization patients, black revascularization patients (OR=1.30, 95% CI 1.26 to 1.34), Hispanic revascularization patients (OR=1.14, 95% CI 1.11 to 1.18), and Asian patients (OR=1.44, 95% CI 1.36 to 1.53) were significantly more likely to undergo carotid stenting. Compared with Medicare revascularization patients, Medicaid patients (OR=1.32, 95% CI 1.27 to 1.37) and self-pay patients (OR=1.18, 95% CI 1.12 to 1.25) were significantly more likely to undergo carotid stenting. These data are summarized in table 5.

    View this table:
    Table 5

    Comparison of demographic characteristics between carotid endarterectomy and carotid artery stenting patients undergoing treatment for carotid artery stenosis in the Nationwide Inpatient Sample

    Disparities by region

    Racial and insurance based disparities for revascularization of asymptomatic disease by region are summarized in table 6. Briefly, racial and insurance based disparities were present in all four regions; west, midwest, northeast and south. In general, white patients were significantly more likely to receive revascularization for asymptomatic carotid artery stenosis than minority groups. For insurance status, Medicare patients were significantly more likely to undergo revascularization for asymptomatic disease than other insurance groups. Insurance based disparities were most marked in the west: the odds of a self-pay patient receiving revascularization for asymptomatic disease compared with a Medicare patient was 0.27 (95% CI 0.24 to 0.31). Black patients in the midwest had the lowest OR for receiving revascularization for asymptomatic disease compared with whites (OR=0.65, 95% CI 0.59 to 0.72).

    View this table:
    Table 6

    Comparison of demographic characteristics between asymptomatic and symptomatic carotid artery stenosis patients undergoing carotid revascularization procedures in the Nationwide Inpatient Sample by region

    Multivariate analysis

    Multivariate analysis demonstrated that Medicaid (OR=0.87, 95% CI 0.83 to 0.92, p<0.0001) and self-pay patients (OR=0.48, 95% CI 0.45 to 0.51, p<0.0001) had a lower odds of being treated for asymptomatic carotid artery stenosis compared with private insurance patients. Black (OR=0.81, 95% CI −0.77 to 0.84, p<0.0001) and Hispanic (OR=0.86, 95% CI −0.83 to 0.90, p<0.0001) patients had significantly lower odds of treatment for asymptomatic carotid artery stenosis compared with white patients.

    Multivariate analysis demonstrated that Medicare (OR=1.10, 95% CI 1.08 to 1.13, p<0.0001), Medicaid (OR=1.31, 95% CI 1.25 to 1.37, p<0.0001), and self-pay patients (OR=1.14, 95% CI 1.07 to 1.22, p<0.0001) had higher odds of carotid artery stenting. Black patients (OR=1.27, 95% CI 1.22 to 1.32, p<0.0001), Hispanic patients (OR=1.09, 95% CI 1.05 to 1.14, p<0.0001), and Asian/Pacific Islanders (OR=1.36, 95% CI 1.25 to 1.47, p<0.0001) had higher odds of carotid artery stenting compared with white patients. These data are summarized in table 7.

    View this table:
    Table 7

    Multivariate logistic regression analysis for indication of revascularization and type of revascularization by demographic covariates

    Discussion

    We found that patients treated for symptomatic carotid artery stenosis were more likely to be minorities and less well insured patients compared with those treated for asymptomatic disease. The insurance based and racial/ethnic disparities seen in this study were consistent across time periods, treatment modality, age groups, and region. These findings suggest that racial and insurance based disparities exist in the utilization of surgical and endovascular carotid revascularization for the treatment of asymptomatic carotid artery stenosis.

    Many factors likely play a role in the disparities seen in our study. First, the underlying assumption of our study was that patients presenting with symptomatic disease would be treated regardless of symptomatic status. This is likely due to the fact that the advantage of surgery over medical therapy is largest among patients with symptomatic disease.10 ,11 ,14 Thus a higher proportion of patients presenting with symptomatic disease will be treated surgically, regardless of insurance status or ability to pay. The fact that there was a higher proportion of minority and less well insured patients in the symptomatic group may be explained by the willingness of surgeons to operate in the situation of poor or no reimbursement as opposed to the situation of asymptomatic disease when medical therapy may be comparable with surgical therapy. Surgeons may be more willing to electively operate on asymptomatic disease only for patients who can pay for surgery.

    Previous studies have demonstrated significant socioeconomic disparities in the treatment of cerebrovascular diseases. Brinjikji et al2 found that patients of lower socioeconomic status were less likely to undergo elective treatment of unruptured aneurysms that those of higher socioeconomic status. Patients of lower socioeconomic status are also less likely to receive intravenous tissue plasminogen activator and mechanical thrombectomy for acute ischemic stroke.5 ,15 ,16 Amaranto et al17 demonstrated that Caucasian race was an independent predictor of surgical intervention for the treatment of carotid artery stenosis. In a study of California hospitals, Kennedy et al18 found that non-white patients had lower rates of carotid endarterectomy and worse surgical outcomes compared with white patients. Skerritt et al19 found that, per 100 000 discharges, racial minorities were less likely to receive carotid endarterectomy compared with white patients. However, this is to be expected as racial minorities are known to have lower rates of carotid disease compared with whites.20 By demonstrating a higher proportion of minorities in the symptomatic cohort, our study suggests that, while they may have lower rates of carotid disease, these groups are less likely to undergo elective surgical and endovascular treatment for asymptomatic disease.

    Our findings are not surprising as minority patients generally have less access to medical care for the treatment of vascular risk factors. For example, Egan et al21 used the National Health and Nutrition Examination Surveys to demonstrated that Hispanic and Black patients were significantly less likely to have adequate control of hypertension and hypercholesterolemia. Zweifler et al22 found that while black patients had a lower prevalence of dyslipidemia, they were less likely to be aware, treated, and controlled for dyslipidemia than white patients. These differences were more marked outside of the stroke belt. In a report from the Center for Disease Control and Prevention, Gillespie and Hurvitz23 found that black patients not only had higher rates of hypertension than white patients, but those with hypertension were less likely to be controlled.

    Less access to imaging likely also plays a small role in the disparities seen in this study. In general, uninsured patients are less likely to undergo imaging for screening purposes than their insured counterparts.24 A Canadian study demonstrated that, even in a system where all patients have healthcare coverage, patients with lower socioeconomic status undergo medical imaging at significantly lower rates than their counterparts of higher socioeconomic status.25 In the case of carotid disease, a recently published study by Cheng et al26 found that carotid artery imaging is under-utilized in minority serving hospitals. In a large study of VA hospitals, Oddone et al27 found that black patients were more likely to present with stroke than white patients, but were less likely to have an imaging study for their carotid arteries, even after adjusting for clinical factors. Less access to the healthcare system coupled with decreased imaging and screening among the uninsured and racial/ethnic minorities may contribute to the lower rates of treatment for asymptomatic carotid artery stenosis among this population in the USA.

    Previously published studies have demonstrated that patients from minority groups and lower socioeconomic strata have less access to advanced surgical techniques and elective surgical procedures.28–31 It is possible that the decreased treatment of asymptomatic disease may be attributed to a lack of access to surgical and endovascular treatments. Patients who lack financial resources may be more likely to opt for not undergoing elective procedures and may opt for conservative management. The majority of the admissions for revascularization of asymptomatic disease in our study were considered elective.

    Our study also demonstrated that on multivariate analysis, non-private insurance patients are more likely to receive carotid stenting than carotid endarterectomy, as are racial/ethnic minorities compared with white patients. There are a number of possible explanations for this finding. First, many private insurers have very select indications for carotid stenting. Hence patients with private insurance may be more likely to receive carotid endarterectomy because stenting is not covered in most situations. Also, surgeons who do offer carotid endarterectomy and not stenting are unlikely to refer the best insured patients for an alternative treatment. For patients with self-pay or poor insurance, referral for stenting is more likely because there will be little or no reimbursement for endarterectomy or stenting.

    Limitations

    Although it would be ideal to compare the demographics of patients undergoing treatment of asymptomatic carotid artery stenosis with the overall population of treatable asymptomatic carotid artery stenosis, this is not possible with the NIS database. The use of symptomatic carotid artery stenosis patients as controls may introduce some selection bias as patients from poorer areas may lack access to surgical treatment of asymptomatic disease and thus may suffer from higher rates of pretreatment mortality. However, this would mean that we are underestimating the disparity. We were unable to determine if lower rates of treatment observed among racial/ethnic minorities and less well insured patients were because of lower rates of detection of carotid artery stenosis or lower access to invasive treatment. It is possible that differences in the incidence of carotid artery stenosis between groups, or more rapid progression of carotid artery stenosis in certain subgroups of patients, may be the cause of some of the disparities seen in this study. This database does not offer any data on presenting condition and degree of carotid artery stenosis, important factors which influence the decision to recommend treatment of asymptomatic disease. Potential coding inaccuracies may also affect the accuracy of this study, as they do any administrative database.32 Lastly, given the large sample size, it is possible that many statistically significant p values may not necessarily be clinically meaningful. For this reason we provided ORs in addition to p values in order to provide a measure of effect size.14

    Our study did not address the role of medical management in the treatment of carotid artery stenosis. Medical therapy has significantly improved since the publication of the Asymptomatic Carotid Atherosclerosis Study (ACAS) trial which has led many experts to re-evaluate the role of medical therapy in the treatment of asymptomatic carotid artery stenosis.14 In fact, improvement in medical therapy has led many to question the relative benefits of surgical revascularization of patients with asymptomatic carotid artery stenosis. Clinical trials comparing current medical therapies with surgical and endovascular revascularization for asymptomatic disease may change current treatment paradigms for treatment of asymptomatic carotid artery stenosis as it is likely that the number needed to treat for surgical revascularization to have any benefit over medical management has increased since the publication of ACAS. By not being able to examine differences in rates of utilization of medical therapy, our study ignores an important facet of treatment of asymptomatic disease. Furthermore, it is important to point out the benefits of revascularization in asymptomatic patients in terms of stroke risk reduction are not as marked as they are for symptomatic patients with 70–99% stenosis. The risks of revascularization surgery for asymptomatic patients are lower than those of symptomatic patients but the benefits are also lower.9–12

    Given the limited benefit of revascularization for asymptomatic disease and improvements in medical therapy, we believe physicians should be more selective regarding patient selection for revascularization of asymptomatic disease. It is interesting to note however that over the course of the study, the number of patients undergoing revascularization for asymptomatic carotid artery stenosis decreased from 123 284 patients in 2005 to 106 883 patients in 2011. This decrease in the number of patients receiving revascularization for asymptomatic disease was steady over the course of the study time period. The number of patients receiving revascularization for symptomatic disease fluctuated between 9500 patients and 11 000 patients over the study, and a greater proportion of patients received revascularization for symptomatic disease over the study period. While the significance of these findings is unclear, it is possible that more patients with asymptomatic disease were treated with medical rather than surgical/endovascular therapy over the study time period.

    Conclusions

    Our findings indicate that racial/ethnic and insurance based disparities exist in the surgical and endovascular treatment of asymptomatic carotid artery stenosis. These differences were independent of age or time period treated. Further studies are needed to determine the underlying causes and solutions for these disparities.

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    Footnotes

    • Contributors WB, AME, DFK, GL, and HJC participated in drafting the article and revising it critically for important intellectual content. These authors made substantial contributions to conception and design, acquisition of the data, and analysis and interpretation of the data. All authors provided final approval of the version to be published.

    • Competing interests HJC: grants/grants pending from Cordis Endovascular*. DFK: consultancy for ev3*, Medtronic*, and Codman*; grants/grants pending from ev3*, MicroVention*, Sequent*, and Codman*; payment for lectures (including service on speakers bureaus) fromMicroVention*; royalties from UVA Patent Foundation*; payment for development of educational presentations from ev3*; and travel/accommodations/meeting expenses unrelated to the activities listed from MicroVention*. GL: consultancy for Edge Therapeutics; payment for development of educational presentations from Covidien/ev3*; and travel/accommodations/meeting expenses unrelated to the activities listed from Boston Biomedica Associates.

    • *Money paid to institution.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data sharing statement The authors will share datasets on request as these were obtained from a publically available administrative database.