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Cost of injuries from a prospective cohort study of North Carolina high school athletes
  1. S B Knowles1,
  2. S W Marshall1,2,3,
  3. T Miller4,
  4. R Spicer4,
  5. J M Bowling5,
  6. D Loomis1,
  7. R W Millikan1,
  8. J Yang6,
  9. F O Mueller7
  1. 1
    Department of Epidemiology, School of Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
  2. 2
    The University of North Carolina Injury Prevention Research Center, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
  3. 3
    Department of Orthopedics, School of Medicine, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
  4. 4
    Pacific Institute for Research and Evaluation, Calverton, MD, USA
  5. 5
    Department of Health Behavior and Health Education, School of Public Health, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
  6. 6
    Department of Community and Behavioral Health, College of Public Health, The University of Iowa, Iowa City, IA, USA
  7. 7
    Department of Exercise and Sport Science, The University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
  1. Dr S B Knowles, Palo Alto Medical Foundation Research Institute, Department of Health Services Research, 795 El Camino Real, Ames Building, Palo Alto, CA 94301, USA; knowless{at}pamfri.org

Abstract

Objective: To estimate the economic cost of injuries in a population of US high school varsity athletes.

Design and Setting: The North Carolina High School Athletic Injury Study, conducted from 1996 to 1999, was a prospective cohort study of injury incidence and severity. A two-stage cluster sampling technique was used to select athletic teams from 100 high schools in North Carolina. An injury cost model was used to estimate the economic cost of injury.

Participants: Varsity athletes from 12 sports: football, girls’ and boy’s soccer, girls’ and boys’ track, girls’ and boy’s basketball, baseball, softball, wrestling, volleyball, and cheerleading.

Main outcome measures: Descriptive data were collected at the time of injury. Three types of costs were estimated: medical, human capital (medical costs plus loss of future earnings), and comprehensive (human capital costs plus lost quality of life).

Results: The annual statewide estimates were $9.9 million in medical costs, $44.7 million in human capital costs, and $144.6 million in comprehensive costs. The mean medical cost was $709 per injury (95% CI $542 to $927), $2223 per injury (95% CI $1709 to $2893) in human capital costs, and $10 432 per injury (95% CI $8062 to $13 449) in comprehensive costs. Sport and competition division were significant predictors of injury costs.

Conclusions: Injuries among high school athletes represent a significant economic cost to society. Further research should estimate costs in additional populations to begin to develop cost-effective sports injury prevention programs.

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Despite the health benefits of sports participation, injury is a detrimental consequence and an important public health problem. Van Mechelen and others proposed a comprehensive approach to sports injury severity that emphasized economic cost as one of six severity markers, along with nature of the injury, level of medical care, time lost from sports participation, working time lost, and permanent disability.14 Economic cost is based on the conversion of the other five markers into an economic estimate. To date, the majority of the sports injury literature in the USA has not addressed the costs associated with sports injuries in a comprehensive manner. Instead, the sports injury literature has generally described injury severity using different definitions based on the nature of the injury and the length of recovery time.510 Using these methods, most high school sports injuries have been considered relatively minor and non-permanent511; however, large costs, including treatment and rehabilitation, may be associated with managing these apparently “minor” injuries.

Prior research has emphasized that interventions such as bicycle helmets and child safety seats are cost-effective because of the high cost of childhood injury.1213 Increased knowledge about the cost of sports injuries can similarly help to target limited resources toward preventing those injuries that are most costly to society. The primary purpose of this analysis was to describe the cost of injuries in a population of high school varsity athletes.

METHODS

Sample selection

Data for this paper came from the North Carolina High School Athletic Injury Study (NCHSAIS), a prospective cohort study conducted from 1996 to 1999. An extensive description of the study methods has been published.14 Briefly, participants were approximately 5013 varsity athletes per school year representing 12 different sports in 100 public high schools in North Carolina: boys’ and girls’ soccer, boys’ and girls’ track, boys’ and girls’ basketball, baseball, softball, wrestling, volleyball, cheerleading, and football.

The sample was selected using a stratified two-stage probability proportional-to-size cluster sampling technique.1415 The sample was stratified by presence of a certified athletic trainer, competition division, geographic region, and average school attendance.14

Aggregate estimates and sample weights

Sample weights were constructed to produce aggregate statewide estimates by multiplying the product of the inverse probabilities of selection in the two stages by the response rates at the school, sport, and athlete levels.14 Normalized weights (sample weights multiplied by the sampling fraction) were used in all analyses in this paper. These weights account for non-response and the complex survey design.14

Definition of injury

A reportable injury was defined as “a result of participation in a high school sport that either limited the student’s full participation in the sport the day following the injury or required medical attention by a medical professional (ie, athletic trainer, physician, nurse, emergency medical technician, emergency room personnel, or dentist)”.14 Injuries such as concussions, fractures, and eye injuries were also reportable, regardless of whether they resulted in lost participation.

Data collection

Injury and risk factor data were collected from three sources: an athlete’s demographic questionnaire, a coach’s demographic questionnaire, and an injury report form. An injury report form was completed for each sustained injury, so an athlete who suffered multiple injuries during one incident had multiple corresponding injury reports. Data were collected by either the school’s certified athletic trainer (69%) or the athletic director (31%).

The NCHSAIS directly assessed several markers of severity, including type of injury, body site injured, level of medical treatment received, and time lost from sports participation. Type of injury and body site injured were used in this analysis to describe the nature of the observed injuries. Time lost from participation was categorized as no time lost, <1 week lost, 1–3 weeks lost, and >3 weeks lost. Type of medical treatment was categorized into three levels based on the highest level of medical care: non-emergency department (ED) medical attention (including doctors’ offices, athletic trainers, or other medical personnel), an ED visit that did not result in hospitalization, and hospitalization.

Revised Injury Cost Model (RICM) methodology

Economic costs were estimated using mean costs for adolescents aged 15–19 from the RICM originally developed for the US Consumer Product Safety Commission (16, 17). Three types of cost were estimated: medical, earnings losses, and reduced quality of life (fig 1). Costs are presented in the following categories: medical, human capital (medical + loss of future earnings), and comprehensive (medical costs + loss of future earnings + reduced quality of life costs).

Figure 1 Derivation of how Revised Injury Cost Model cost estimates were adapted to the North Carolina High School Athletic Injury Study dataset. QUALY, quality-adjusted life year.

Medical costs

To develop estimates of long-term medical costs, the cost model used data from the 1992–1994 Civilian Health and Medical Program of the Uniformed Services (CHAMPUS) summaries of military retirees and their dependents (including children), the 1987 National Medical Expenditure Survey, the 1987–1992 National Hospital Discharge Survey, the 1995–1996 National Electronic Injury Surveillance System (NEISS), as well as pooled five-state hospital discharge data (covering the years 1989–1995).1617 Medical costs were adjusted to reflect North Carolina costs based on the ratio of the consumer price index for medical care for southern US urban cities for July 1999 to the corresponding overall consumer price index for the USA.18

Loss of future earnings

The RICM based loss of future earnings on the product of the probability of immediate work loss, the days lost if a loss occurs, and the average value of a day’s work. The RICM calculated the average daily value of wage and household work using age- and gender-stratified data from the 1987–1992 National Health Interview Survey and the US Bureau of Labor Statistics.1617 Work losses in this analysis represent an approximation, as there is no economic value formally associated with schoolwork. The dollar values assigned represent earnings losses for employed persons of high school age, adjusted for part-time status. The costs also include earnings losses of parents and other caregivers who must take time off work to take injured school children to medical appointments and provide other care. Future earnings losses were adjusted to North Carolina wages based on the ratio of the average annual personal income per capita for North Carolina for 1999 and the corresponding average for the USA.19

Quality of life

The estimates of reduced quality of life and pain and suffering costs were based on the quality-adjusted life years (QALYs) lost due to injury. Lost QALYs are computed using a seven-dimensional model that includes physician ratings1617 on functional losses in: mobility, cognition, bending and grasping, pain, sensory, cosmetic (resulting in probability of impairment), and the ability to work (based on probability of disability). The combination of these seven dimensions, when multiplied by the total number of years of life remaining, result in an estimated lost QALY. The estimated age-adjusted value for one QALY was $127 236, adjusted for 1999 inflation.20

Although QALY-based costing is not the default method for valuing quality of life loss in the RICM, QALY estimation is recommended by the Panel of Cost-effectiveness in Health and Medicine21 and seemed more appropriate than the default costing based on jury awards for non-economic damages in consumer product injury lawsuits.

Computing cost per injury

To assign costs to the observed injuries, a three-way matrix was created based on NCHSAIS data about the body part injured (46 categories), type of injury (16 categories), and level of medical care received (three categories), and was stratified by gender (using RICM costs for ages 15–19). NCHSAIS codes for body part injured and type of injury were re-coded to match the NEISS diagnostic codes used in the RICM. Highest level of medical care was based on NCHSAIS categorizations of non-ED, ED only, and hospitalization. As a result, mean medical, lost earnings, and reduced quality of life costs, stratified by gender, were applied to each possible matrix combination.

A total of 592 of the reported injuries (19.8%) in this study were initially not assigned costs. This included 561 (18.8%) that were missing data from at least one of the injury descriptors and 23 that were missing all injury descriptor data. The remaining eight uncosted injuries were either too minor or the combination of descriptors did not make sense (eg, concussion to pelvic region). For the 569 injuries that were not missing all injury descriptor information, we imputed the missing values based on the mean medical, human capital, and comprehensive costs using a hierarchy of injury type, body part injured, and level of treatment from the injuries that were assigned costs. For example, a reported fracture with no assigned body part or level of treatment (and therefore missing cost data) was assigned the mean cost of a fracture in this study. Although they were included in the total reported aggregate costs, we excluded the 569 injuries from the regression analyses because including them would result in the same estimated mean costs (based on the imputation using means) but the resulting variance estimates would be incorrect. There were no meaningful differences in the covariate patterns between the injuries with estimated costs (n = 2398) and the injuries for which costs could originally not be estimated (n = 592).

The cost data were log-transformed before analysis on the basis of regression diagnostics, and outliers that indicated the data, as is often the case with cost estimates, were not normally distributed. Costs are presented in 1999 NC dollars, adjusted for inflation.1819

Predictors of injury cost

The following predictors of cost were evaluated: sport, gender, grade, multiple sport participation, coaching experience, qualifications, and training (coach EQT), years of playing experience, prior injury, age, body mass index for age (BMI, centiles), and competition division. Study year was also included in the full model, but there were negligible cost changes over the course of the study, so specific results by year are not presented. A detailed description of these intrinsic and extrinsic predictors has been published previously but they are briefly described here.22

Prior injury included history of the following injuries: knee, ankle, shoulder, wrist, elbow, fracture, concussion, heat-related illness, and others. BMI was estimated as age- and gender-specific centiles.22 Coach EQT was based on coaches’ answers to five yes/no questions: completion of at least a college degree, completion of a coaching class, current certification in first aid or cardiopulmonary resuscitation, at least 1 year of coaching experience in that sport, and at least 1 year of playing experience in that sport. Coach EQT was categorized as “low” if they answered yes to up to two questions, “medium” if they answered yes to three questions, or “high” if they answered yes to four or five questions. Competition division (1A–4A) was based on school enrollment.

Statistical methods

Multivariate linear regression models on log-transformed costs were used to identify important predictors of injury cost. The models adjusted for sport, injury history, multiple sport participation, age, years of playing experience, BMI, grade, coach EQT, competition division, and study year. Separate adjusted mean costs were estimated for all 12 sports and for the eight gender-comparable sports: boys’ and girls’ basketball, boys’ and girls’ soccer, boys’ and girls’ track, and baseball and softball. Statistical analyses were performed using SAS-Callable SUDAAN V.8.0 in order to produce valid variance estimates.23

RESULTS

An estimated 15 038 athletes were observed for all 12 sports over the 3-year study period. There were 2990 injuries reported for the entire study period; some athletes sustained multiple injuries. We excluded from the regression analyses the 592 injuries for which cost data were originally not estimated. Most injuries (77.5%) were medically treated outside the ED, 19.5% were treated in the ED, and 3.0% required hospitalization.

For the study population, the medical, human capital, and total economic costs per year were $940 608, $4.2 million, and $13.7 million, respectively. Per athlete, the yearly medical cost was $187, human capital cost was $838, and the comprehensive cost was $2733. Annually statewide, this translated into $9.9 million in medical costs, $44.7 million in human capital costs, and $144.6 million in comprehensive costs.

Nature of the injury

The ankle, knee, and shoulder were the most commonly injured sites of the body and, of these, shoulder injuries had the highest mean comprehensive cost per injury (table 1). Sprains were the most common injury and accounted for the greatest percentage of costs, followed by strains and bruises.

Table 1 Distribution and mean comprehensive cost of specific severity markers (n = 2990 injuries), North Carolina High School Athletic Injury Study, 1996–1999

Time lost from sports participation

About one in five injuries resulted in no lost time; about 11% resulted in more than 3 weeks lost (table 1). Knees and fractures were the most common injury site and type of injury that resulted in more than 3 weeks lost participation (25.0% and 41.7%, respectively). When site and type of injury were combined, other types of knee injury, particularly injuries to the knee ligaments, resulted in more than 3 weeks lost (15.0%).

Overall estimated costs of injury

Table 2 shows the exponentiated adjusted mean medical, human capital, and comprehensive costs stratified by the predictor variables. The adjusted mean medical cost per injury was $709 (95% CI $542 to $927), the adjusted mean human capital cost per injury was $2223 (95% CI $1709 to 2893), and the adjusted mean comprehensive cost per injury was $10 432 (95% CI $8062 to $13 449) (table 2).

Table 2 Exponentiated adjusted mean medical costs, human capital costs, and comprehensive costs (n = 2398 injuries*), North Carolina High School Athletic Injury Study, 1996–1999

Comprehensive costs

Sport, competition division, and coach EQT were strong predictors of the adjusted mean comprehensive cost (table 2). For intrinsic risk factors, the highest adjusted mean comprehensive costs were associated with having a prior injury, 2–4 years of playing experience, being 16 years of age or younger, being overweight, and playing a single sport, although there were no significant differences between adjusted mean comprehensive costs between levels of each risk factor nor were they significant predictors of the comprehensive cost. The same pattern was observed for medical costs and human capital costs, with the exception of BMI. Being underweight, rather than overweight, was associated with the highest adjusted mean medical costs.

Among extrinsic risk factors, 9th–10th graders, low coach EQT, and division 1A competition division had the highest adjusted mean comprehensive cost. Wrestling had the highest cost per injury, followed by football. There were significant differences between adjusted mean comprehensive costs (and medical and human capital costs) within the levels of sport, competition division, and coach EQT, but not within grade.

For all 12 sports, the mean medical cost for boys was higher than for girls (p<0.01) (table 3). Gender and age were the only significant predictors of the adjusted mean comprehensive cost. When restricted to gender-comparable sports, the gender difference decreased slightly but remained significantly different (p<0.01), and gender and competition division, but not age, remained significant predictors.

Table 3 Exponentiated adjusted mean medical, human capital, and comprehensive costs, associated with gender, adjusted for other risk factors, in 1999 dollars (n = 2398 injuries*), North Carolina High School Athletic Injury Study, 1996–1999

DISCUSSION

This study quantified the cost of sports injuries in a population of high school varsity athletes. Most injuries resulted in less than 1 week’s loss of sports participation. However, even these relatively “minor” injuries resulted in a substantial cost to society. These injuries resulted in approximately $941 000 per year in medical costs ($187 per athlete), $4.2 million per year in human capital costs ($838 per athlete), and $13.7 million per year in comprehensive costs ($2733 per athlete).

Significance of findings

Most injuries were sprains and strains and occurred to the ankle or the knee, reflecting a common finding in the literature.5892430 Sport was a significant predictor of cost. Although wrestling was associated with the highest mean costs per injury, it accounted for only 7.2% of all injuries and 7.1% of comprehensive costs. Football, which accounted for 41.4% of observed injuries, accounted for 57.0% of medical costs, 58.1% of human capital costs, and 53.8% of comprehensive costs.

Key points

  • The total annual medical cost of injuries in the NCHSAIS athletes/study population/study’s athletes was $940 608.

  • The total annual human capital cost was $4.2 million.

  • The total annual comprehensive cost was $13.7 million.

  • Although wrestling injuries were the most expensive per injury, football injuries accounted for 53.8% of the comprehensive costs.

The overall cost of high school sports injuries has not, until now, been adequately investigated or reported in the literature. Other studies have attempted to quantify medical costs by retrospectively examining insurance claims, but have underestimated medical costs by including only those injuries for which an insurance claim was filed.283132 The only national estimate of sports-related medical costs comes from the 1997–1998 National Hospital Ambulatory Medical Care Survey, which estimated $680 million in medical costs for the 2-year period of 1997–1998.33 However, this figure excluded costs associated with lost wages and reduced quality of life.

Strengths and limitations

These cost data are subject to important limitations. We did not track individual expenditures in this population but estimated them from a cost model. As part of this, we did not estimate the cost of lost earnings among athletes who may or may not have also held part-time employment. As a result, we presented the loss of future earnings as part of a broader human capital cost. Finally, the cost estimates also exclude the time that coaches and school administration spent in investigating the injury event and filing paper work. Despite the limitations of the RICM, these estimates provide strong evidence that sports injuries in this population incur a substantial cost to society.

Very few studies have attempted to quantify the economic severity of high school sports injuries in the USA. Most used time lost from sports participation rather than cost as the primary marker of severity, and our results suggest that this may be misleading. The results of this study also suggest that ED-based studies may miss up to 70% of injuries, thereby underestimating both the incidence and cost of injuries. Finally, although these results may not be generalizable to other study populations, the RICM methods can and should be adapted and applied in multiple settings.

IMPLICATIONS FOR PREVENTION

The annual comprehensive cost of high school sports injuries in this population was estimated at $13.7 million and $2733 per athlete. Our findings highlight the fact that even so-called relatively “minor” injuries result in significant costs to society. The comprehensive method used in this analysis should be applied in different populations as well as national athlete samples to provide additional critical information about the economic burden of sports injuries. This increased knowledge can help to direct limited research funding to developing cost-effective interventions to reduce injury risk among young athletes.

Acknowledgments

We express our appreciation to Nancy L Weaver, William Kalsbeek, John Sideris, Brian Sutton, Dick Knox, and William E Prentice Jr. We acknowledge the invaluable contribution of the high school athletic trainers and athletic directors who participated in this project.

REFERENCES

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Footnotes

  • Funding: This study was supported by a grant from the National Institute of Arthritis, Musculoskeletal, and Skin Diseases (R01/AR42297) to the University of North Carolina Injury Prevention Research Center (R49/CCR402444). The funding sources had no involvement in the preparation of this manuscript.

  • Competing interests: None.

  • Abbreviations:
    BMI
    body mass index
    coach EQT
    coaching experience, qualifications, and training
    ED
    emergency department
    NCHSAIS
    North Carolina High School Athletic Injury Study
    QALY
    quality-adjusted life year
    RICM
    Revised Injury Cost Model

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