Abstract
Background A concussion is considered a mild traumatic brain injury that may cause physical, cognitive, affective, and sleep dysfunction. Physical therapists have been identified as health care providers involved in the multidisciplinary care of a patient with concussion.
Objective The purpose of this study was to describe the current attitudes and beliefs, knowledge, and practice of physical therapists in the treatment of patients with concussion.
Methods A 55-question electronic survey divided into 6 sections—(1) demographics, (2) current practice in concussion, (3) youth concussion legislation, (4) attitudes and beliefs toward concussion management, (5) concussion knowledge, and (6) clinical decision making—was developed and distributed online through selected American Physical Therapy Association sections.
Results A total of 1,272 physical therapists completed the survey. Seventy percent of the respondents (n=894) reported having concussion training. Although supportive of the role of the physical therapist in the treatment of a person with concussion, the respondents demonstrated less confidence when making return-to-play decisions. Respondents correctly answered, on average, 13 (out of 15) concussion knowledge questions, with gaps exhibited in understanding the clinical utilization of concussion severity scales, the conservative treatment of youth who sustain a concussion, and anticipated normal computed tomography and magnetic resonance imaging after a concussion. When provided with clinical scenarios, respondents were able to recognize when a referral to a physician was indicated; however, they demonstrated variability in identifying a need for vestibular or manual physical therapy.
Limitations Convenience sampling was utilized, limiting generalizability of the results of the study to the physical therapy profession as a whole.
Conclusion Physical therapists demonstrated a solid foundation of concussion knowledge, but gaps still existed. Future professional development opportunities should be developed to target identified gaps in knowledge and current practice patterns.
Concussions are a public health priority.1 A concussion, a type of traumatic brain injury, is defined as a complex pathophysiologic process affecting the brain induced by traumatic biomechanical forces.2 The incidence of concussion is estimated to be 100 to 300 cases per 100,000 people; however, not all concussions are evaluated in a hospital, leading to a projected incidence of 600 cases per 100,000 people.3 Despite the amount of attention given to concussions occurring in sports, concussions may happen at any age and most commonly occur secondary to falls and motor vehicle accidents.3 Children and adolescents are at increased risk of sustaining a concussion and take longer to recover compared with adults.2
The effects of sustaining a concussion typically result in a rapid onset of neurological symptoms (eg, headache, irritability, drowsiness) that resolve spontaneously in most people within 10 to 14 days.4 Postconcussive syndrome occurs when symptoms persist and may include emotional disruptions, sleep disturbances, somatic symptoms, and cognitive symptoms.5
Despite the significant amount of research that has been published over the last several years, the clinical management of concussion continues to be challenging.6 A single gold standard test to diagnose a concussion does not exist, and standard neuroimaging (computed tomography [CT], magnetic resonance imaging [MRI]) is typically normal and uninformative after a concussion.2 The current diagnostic process includes a detailed account of the concussion injury, symptom reporting, and examination results, including neurocognitive, balance, vestibular, and exertional testing.2,7–10 Once a concussion is diagnosed, current recommendations promote cognitive and physical rest until the patient is asymptomatic, followed by a graded program of exertion prior to medical clearance and return to play.2,11
Attempts to improve the medical treatment of patients with concussion include the publication of international consensus documents and guidelines and educational efforts provided by professional associations and governmental agencies.2,4,8,11–15 Despite the wide availability of concussion information, reports of limited understanding and lack of following published guidelines by health care professionals continue to exist. Physicians working in an emergency department have demonstrated a wide variation in recommending cognitive rest and a graduated return to play following concussion, with fewer than 25% utilizing nationally recognized guidelines.16 Only 25% of coaches and sports trainers from Australia recognized that younger athletes take longer than adults to recover after sustaining a concussion.17
The American Physical Therapy Association (APTA) House of Delegates, in 2012, passed RC 14-12 (The Physical Therapist's Role in Management of the Person With Concussion),18 which outlined the participation of the physical therapist as a member of a multidisciplinary team in the education, prevention, and management of concussion. Evidence exists on intervention strategies commonly utilized by physical therapists to manage the somatic symptoms experienced by patients after concussion, including vestibular and balance rehabilitation, manual therapy, and graded exertional training.10,19–22 Limited information has been reported on what physical therapists know about concussion. In a group of Irish chartered physical therapists employed with a specialty in sports and exercise medicine (n=95), merely one-third of respondents were aware of international concussion guidelines.23 In another study, only 25% (n=118) of physical therapist students from New Zealand, prior to attending a training session, correctly identified the recommendation for physical and cognitive rest immediately after sustaining a concussion.24 Limited representation of the physical therapy profession as a whole was noted in both of these studies because only physical therapists with a specialty in sports or students participating in sports medicine training were sampled. No studies could be located describing concussion management practices of physical therapists within the United States.
Knowledge itself is not enough to change the behavior of health care professionals. The theory of planned behavior (TPB) is a commonly used behavioral theory to understand sports injury prevention, including concussion.25 The TPB posits that the primary predictor of behavior is the intention to perform that behavior, and intention is directly predicted by 3 factors: attitudes, subjective norms, and perceived behavioral control.26 Attitudes reflect an individual's appraisal of the outcomes of performing the behavior of interest.26 Subjective norms are the perceived pressures felt by a person to perform the behavior from others whose opinions and behaviors are considered important.26 Perceived behavioral control is a person's belief of self-efficacy or ability to perform the behavior.26 Attitudes, subjective norms, and the perceived behavioral control of a health care provider may lead to inappropriate treatment of a patient with a concussion.
Recognizing the inconsistencies in concussion management, professional and amateur sports organizations have modified the rules of play and implemented concussion policies and procedures.27–29 Youth concussion legislation has been passed in all 50 states, and federal legislation is currently pending.30,31 The key tenets of youth concussion legislation promote mandatory education for coaches, parents, and the athlete; immediate removal from play if a concussion is suspected; and return to play after medical clearance from a qualified health care professional trained in concussion management.32,33 Prematurely allowing a youth athlete to return to play after a concussion can have detrimental effects, including death.34 In order to serve as an effective member of a multidisciplinary team caring for a person with a concussion, physical therapists must have contemporary knowledge of evolving concussion care. Further description of attitudes and beliefs, subjective norms, and perceived behavioral control of physical therapists toward concussion management provides the opportunity to explore the possible behavioral intentions behind the physical therapists' involvement in concussion. The success of physical therapy intervention for a patient with concussion is dependent on making appropriate individualized clinical decisions within a legal and ethical context, especially regarding return to play. Opportunity exists for the profession of physical therapy to actively treat patients with movement dysfunction secondary to the effects of a concussion. The purpose of this study was to describe the current attitudes and beliefs, knowledge, and practice of physical therapists in order to gain further understanding of concussion management within the physical therapist profession.
Method
Survey Development
We developed an electronic survey questionnaire utilizing concepts from previously published studies on concussion knowledge, attitudes and beliefs, and practice completed by physicians, physical therapists, and athletic trainers.23,35,36 The survey was reviewed by 3 experts who have a publication record and expertise in concussion and survey methodology and pilot tested for question clarity and readability with 6 faculty from the primary investigator's institution. All suggestions were considered, and modifications were made with the authors' consent (eAppendix).
Respondents were prompted to respond to every question provided in the survey before the next set of questions was presented. A respondent could answer a maximum of 55 questions (depending on skip patterns) categorized into 6 sections: (1) demographics, (2) current practice in concussion, (3) youth concussion legislation, (4) attitudes and beliefs toward concussion management, (5) concussion knowledge, and (6) clinical decision making.
Demographics (questions 1–8).
The demographics section consisted of 8 questions, including sex, age, and education.
Current practice in concussion (questions 9–25).
Depending on responses, up to 17 questions were asked to garner current practice information, including primary practice state, years of experience, clinical experience, APTA membership (including sections), clinical specialty, concussion referral patterns, and types of intervention most commonly implemented. We determined 8 hours of clinical practice to be the least amount of practice required to receive additional concussion practice questions in order to ensure a minimal amount of clinical practice.
Youth concussion legislation (questions 26 and 27).
Respondents who reported seeing at least one patient with a concussion over the last year were asked up to 2 questions regarding their knowledge of concussion legislation. Respondents were asked if they were aware of the presence of youth concussion legislation in their respective state. If respondents answered affirmatively, they were asked whether their state legislation authorized physical therapists to clear youth athletes for return to play.
Attitudes and beliefs toward concussion management (questions 28–36).
Utilizing the TPB as a foundation for inquiry, 9 questions were asked about the respondent's attitudes and beliefs (questions 31–34), the presence of subjective norms (questions 35 and 36), as well as perceived behavioral control (questions 28–30) toward concussion management.
Concussion knowledge (questions 37–51).
Content knowledge of concussion management was asked in a series of 15 true or false questions where respondents also had the opportunity to answer “unsure.” Questions and answers were developed from information available through the Centers for Disease Control and Prevention (CDC) HEADS UP website and from the Concussion in Sport Group (CISG) Consensus Statement.2,37 The CDC HEADS UP programs translate current concussion science into information designed for specific audiences, including health care professionals.38 The CISG, an international multidisciplinary group of experts in concussion, summarizes current evidence regarding sports concussion and has provided consensus-based guidelines since 2001.2,4,8,12 A total knowledge score was calculated by adding up the 15 questions that were answered correctly, with a higher score reflecting more knowledge (possible range of correct answers=0–15).
Clinical decision making (questions 52–55).
In order to describe physical therapists' clinical decision making when treating a person with concussion, 4 case scenarios were provided, and respondents were asked to make the most appropriate clinical decision based on the limited information provided. All case scenarios involved patients who had sustained a concussion and had a primary impairment (eg, cervical, vestibular, or exertional symptoms) when seen in an outpatient clinic for physical therapy.
Survey Dissemination
In order to gather a convenience sample of physical therapists, a survey invitation was distributed through APTA sections, including section listserves (Acute Care, Education, Geriatrics, Home Health, Neurology), electronic newsletters (Orthopaedics, Pediatrics), and direct emails sent to section membership (Private Practice, Sports). Sections were selected based on potential membership interest in concussion and the ability to disseminate the survey. The invitation provided a brief background on the survey and encouraged physical therapists with or without experience in concussion management to participate. Interested respondents clicked on an electronic link that led them to the survey description, and they were able to provide informed consent and access the survey. Surveys were completed anonymously via Qualtrics Online Survey Software (Qualtrics LLC, Provo, Utah). Utilizing Dillman's tailored design method to maximize responses, reminder emails or listserve posts were communicated 2 additional times (1 week apart) from the original dissemination date.39 The survey was open for respondents to complete from March through May 2014.
Data Analysis
Data were analyzed using IBM SPSS, version 21.0 (IBM Corp, Armonk, New York). Descriptive statistics were used to summarize the distribution, central tendency, and dispersion of respondents' responses.
Role of the Funding Source
The Physical Therapy Department at the University of Michigan–Flint provided financial support for the study.
Results
Demographics
One thousand four hundred sixteen respondents started the survey; however, 144 questionnaires were partially completed and not included in further analyses, leaving 1,272 physical therapist respondents (711 female and 561 male) included in the results. The average age of the respondents was 42 years (SD=11). More than 50% of the respondents had a clinical doctorate in physical therapy, and one-third had more than 21 years of experience as a physical therapist. Seventy-five percent of the respondents reported formal training in sports medicine, and 70.3% reported formal training in concussion. Approximately one-third (32.4%) of the respondents reported certification through the American Board of Physical Therapy Specialties (ABPTS). Private outpatient or group practice was the most prevalent primary work setting (43.8%, n=557), followed by health system or hospital-based outpatient (25.6%, n=326). Respondent demographic characteristics are shown in Table 1.
Respondent Demographics (n=1,272)a
Current Practice in Concussion
Eighty-five percent (n=1,078) of the respondents reported working in the clinic at least 8 hours per week. Twenty-eight percent (n=303) of the respondents reported seeing no patients with concussion. Fifty-five percent of those in clinical practice (n=590) reported seeing 1 to 12 patients with concussion in the last calendar year, and 17.1% (n=185) reported seeing 13 patients or more. Of the 775 physical therapists who reported seeing at least one patient with concussion in the last calendar year, the majority of patients were referred from a primary care practitioner (43.5%, n=337) or a neurologist (20.1%, n=156). One-third of those respondents seeing at least one patient (33.9%, n=263) reported the average amount of time between sustaining a concussion and time of initial evaluation was ≥3 weeks, whereas the majority (66.1%, n=512) reported a time period of less than 3 weeks. The respondents reported utilizing multiple interventions (not mutually exclusive), including graded exertional training (54.1%), vestibular and balance rehabilitation (48.6%), manual therapy (43.5%), and “other” (13.6%). Practice characteristics of the respondents are described in Table 2.
Characteristics of Respondents Who Reported Seeing at Least One Patient With Concussion (n=775)
Youth Concussion Legislation
Of the respondents who reported at least 8 hours of clinical practice per week and seeing at least one patient with a concussion over the last year, two-thirds (n=510) correctly identified whether the state in which they practice has a concussion law specifically addressing youth concussions. Of those who correctly identified their state as having a concussion law (n=510), 58.2% (n=297) correctly identified whether physical therapists are considered health care professionals authorized to make return-to-play decisions in their individual state. Results of the legislative questions are shown in Table 3.
Respondents' Legislative Knowledge
Attitudes and Beliefs Toward Concussion Management
The respondents overwhelmingly held the attitude that physical therapists should be one member of a multidisciplinary team (“strongly agree” and “agree”=96%, n=1,222) and that concussions have a significant impact on the health of individuals and society (“strongly agree” and “agree”=95.9%, n=1,219). Fewer respondents agreed that physical therapists should be allowed to determine return to play for an athlete who has sustained a concussion (“strongly agree” and “agree”=79.3%, n=1,009). The majority of respondents believed that physical therapists should be more involved in concussion management (“strongly agree” and “agree”=88.3%, n=1,123). When investigating subjective norms, fewer than two-thirds of respondents (“strongly agree” and “agree”=58.1%, n=739) reported that their colleagues say physical therapists should be more involved in concussion management, and slightly fewer reported that their clinic administrator says physical therapists should be more involved in concussion management (“strongly agree” and “agree”=51.8%, n=659). In regard to perceived behavioral control, a total of 82.4% (n=1,048) of respondents strongly agreed or agreed that they were confident in their ability to recognize a concussion. Slightly fewer respondents reported confidence in their knowledge of concussion management (“strongly agree” and “agree”=69.2%, n=881), and even fewer reported confidence in their ability to provide clearance for return to play in a young athlete (“strongly agree” and “agree”=58.5%, n=744). When asked to rate the likelihood of their engagement (behavioral intent) in treatment of a patient with concussion in the next year, the respondents (n=775) scored an average of 8.1 (SD=2.8, range=0–10), with 54.1% (n=419) indicating a rating of 10 (“very likely to engage”). Results from the attitudes and beliefs questions are shown in Table 4.
Respondents' Attitudes and Beliefs (n=1,272)
Concussion Knowledge
Out of 15 concussion questions, respondents averaged 13.4 (SD=1.4, range=5–15) correct answers. More than 97% of the respondents correctly identified the multitude of symptoms that may appear after a concussion, and more than 94% correctly identified the utilization of multiple assessment tools in the evaluation a patient with concussion. Three questions were answered incorrectly or “unsure” by more than 25% of the respondents. Sixty percent (n=757) of the respondents were unsure or believed that concussion management should be based on concussion severity scales. Thirty-nine percent (n=501) were unsure or believed that concussion sustained in youth should not be managed more conservatively than a concussion sustained in adulthood. Twenty-eight percent (n=361) of the respondents answered “false” or “unsure” to the question “A concussion is usually associated with a normal CT scan and/or MRI.” Results of the 15 knowledge questions are shown in Table 5.
Respondents' Knowledge of Concussion (n=1,272)a
Clinical Decision Making
When provided with a patient scenario where the patient's symptoms were worsening despite complete physical and cognitive rest, the majority of respondents (89.8%, n=1,142) identified that the most appropriate action was to refer the patient to a physician. In the second scenario, where the patient had ongoing vestibular symptoms, 48.1% (n=612) of the respondents identified a referral to a vestibular physical therapist, and 43.7% (n=556) selected to refer the patient to the physician as the most appropriate action. The third scenario presented a patient who continued to have symptoms of cervicogenic dizziness. One-half (n=635) of the respondents indicated a referral to a manual physical therapist, whereas 18.6% (n=237) selected to refer the patient to a physician as the most appropriate action. In the last scenario, in which the patient showed resolution of presenting symptoms, 60% (n=763) of the respondents identified a referral for graded exertional training, and 30.2% (n=384) indicated discharge from physical therapist services with no further referral as the most appropriate action. Results of the clinical scenarios are shown in Table 6.
Respondents' Selected Action Based on Clinical Scenarios (n=1,272)
Discussion
Attitudes, Beliefs, and Knowledge of Concussion
Physical therapists have been recommended to participate as a member of a multidisciplinary team caring for a person who has sustained a concussion.18 The results of our study suggest that physical therapists are engaged in, hold positive attitudes toward, and have a strong foundational knowledge of concussion management. The respondents correctly recognized the myriad of symptoms that a person with a concussion may have, as well as the appropriateness of a comprehensive examination including neurocognitive assessment, balance testing, and self-reported symptoms.2,6–9 Respondents also reported utilizing a multifaceted approach, including vestibular and balance rehabilitation, manual therapy, and exertional training, when treating a patient with the physical symptoms of concussion.2,10,19–22
Despite the amount of clinical experience reported by the respondents, gaps in knowledge were identified. Based on current evidence, the routine use of neuroimaging (CT or MRI) with a suspected concussion is not recommended; however, more than one-quarter of the respondents were unaware that concussion is usually associated with a normal neuroimaging.8 Even though ordering neuroimaging may not be within the current scope of physical therapist practice, physical therapists should recognize appropriate utilization, be able to interpret results, and be aware of emerging neuroimaging technology.6 The use of concussion severity scales to guide treatment has been replaced by the recommendation of individualized treatment plans based on the results of a clinical examination.8 However, 40% of the respondents reported concussion severity scales were appropriate to use in clinical care. In comparison, 56% of Irish physical therapists specializing in sports agreed that grading a concussion as simple or complex was correct.23 In contrast, 11.9% of US physicians reported using grading scales to make return-to-play decisions.40 Current consensus-based guidelines emphasize the need for more conservative treatment for those athletes under the age of 18 years, yet specific evidence-based protocols do not exist.2,11 Conservative treatment recognizes that the recovery time line is expected to be longer in youth athletes, yet more than one-third of the respondents were unsure or believed that concussion sustained in youth should not be managed more conservatively than a concussion sustained in adulthood. A serious consequence of this belief is second impact syndrome.34 Although the overall incidence is rare, second impact syndrome occurs when a youth athlete returns to play after an incomplete recovery from a previous head injury, leading to death or severe disability.34
Beyond understanding the gaps in knowledge, further description of attitudes, subjective norms, and perceived behavioral control also can serve to inform the profession. Respondents generally held positive attitudes toward concussion, demonstrating high agreement with APTA policy on the involvement of physical therapists in concussion management.18 More than half reported positive subjective norms toward concussion management from their colleagues and clinic administrators. Regarding issues of control, respondents demonstrated more confidence in recognizing a concussion than determining return to play. A similar pattern was observed in pediatricians who reported confidence in recognizing the symptoms of concussion (94.9%) compared with being confident in providing written return-to-play instructions (77.8%).41 Providing a context of the positive attitudes, supportive subjective norms, and the presence of self-efficacy may provide partial explanation of the behavioral intent that more than one-half of the respondents reported they were “very likely” to engage in concussion over the next year.
Youth concussion legislation mandates clearance for return to play to be made by a qualified health care professional. Approximately two-thirds of respondents correctly identified that their state had concussion legislation compared with 26.6% of pediatricians who were familiar with their state concussion legislation.41 The specifics of concussion legislation and administrative rules vary from state to state, and based on our review of individual state legislation and administrative rules, we believe physical therapists are not authorized to clear a youth athlete for return to play in 28 states. Physical therapists who are unaware of the laws within their state may not be taking full opportunity to provide return-to-play clearance when indicated or may be placing themselves at risk if they are unaware of their own state's legislation.
Describing the knowledge gap, behavioral influences, and current legislative issues may help to optimize knowledge translation (KT) initiatives. Knowledge translation is an active process that facilitates the introduction of new evidence into practice and can identify ideal strategies to close the gap between research and clinical practice.42 This study serves to describe current knowledge and practice of physical therapist and concussion, one of the steps in the knowledge-to-action framework, a commonly utilized structure to create KT initiatives.43 National efforts such as the CDC HEADS UP campaign have recognized the necessity for effective KT efforts. Physicians who were exposed to the HEADS UP campaign were significantly less likely to recommend return to play the day after a concussion, which is consistent with current guidelines.35 Knowledge translation efforts, such as interactive educational sessions, printed materials, utilization of opinion leaders, and working groups, have been effective in changing physical therapists' knowledge and practice.44 Any KT efforts designed for physical therapists and concussion should implement evidence-based strategies into their process.
Practice and Clinical Decision Making in Concussion Management
A lack of evidence currently exists on the optimal timing of physical therapy, as the current treatment paradigm is complete physical and cognitive rest until asymptomatic.2 Two-thirds of the respondents reported seeing the majority of their referrals less than 3 weeks postinjury, which is surprising because the majority of concussion symptoms resolve within 2 weeks.4 The majority of respondents reported receiving patient referrals from primary care providers. In a survey of pediatric providers, 17% of the respondents did not recognize vestibular disorders or abnormal eye tracking as related to concussion.36 Physical therapists are in a position to serve as a health care provider for a patient with a concussion who has physical symptoms such as dizziness, headache, cervical impairments, and imbalance after concussion.22
Making informed clinical decisions is imperative in clinical practice.45 With limited information, the presented cases attempted to characterize the common concussion symptom clusters experienced by patients referred for physical therapy. Although the majority of respondents were able to identify a referral to a vestibular or manual physical therapist when potentially indicated, approximately 50% of the respondents chose to refer the patient back to the physician. When graded exertional training was potentially indicated, one-third of the respondents recommended discharge from physical therapy.6 Different concussion trajectories, used to describe the heterogeneous symptoms that a patient with concussion may have, can be implemented as a framework and may assist the physical therapist in selecting the most appropriate intervention within his or her area of expertise or in referring the patient to a different health care professional.
Future Directions
Future research should focus on evaluating KT initiatives that address the knowledge gaps, in particular those identified in this study on the utilization of neuroimaging, concussion severity scales, and the need for conservative management in youth. Opportunities exist to increase the amount of knowledge and self-efficacy that physical therapists have toward treating a patient with concussion. Advocating for the benefits of physical therapy at both an individual patient level and a societal level will promote improved patient care. Future research could further investigate the knowledge and adherence that physical therapists demonstrate with concussion guidelines and the specific examination tools utilized to assess a patient with concussion.
Limitations
The survey questionnaire utilized in the study was not previously validated, and despite our efforts during the pilot testing to ensure clarity, we recognize that the questions may have been subject to various interpretations by the respondents. We were unable to calculate the true response rate of the survey. Surveys were distributed electronically through select APTA sections. Respondents may have belonged to more than one section, and some respondents were not APTA members, resulting in our inability to determine the exact number of eligible survey recipients. We recognize that our results may not represent the physical therapy profession at large. Even though all physical therapists, whether experienced with concussion or not, were encouraged to complete the survey, sampling bias may have occurred in that the only respondents who participated were those interested in the topic of concussion.
In conclusion, the results of our survey suggest that physical therapists demonstrated a solid foundation of concussion knowledge and are confident in their assessment and management in a person with concussion. Respondents believed that physical therapists should be involved in the care and management of people with concussion, yet demonstrated a lack of confidence in making return-to-play decisions. Gaps existed in the utilization of concussion severity scales, management of youth concussion, and use of neuroimaging for the diagnosis of concussion. Recognizing the appropriate utilization for vestibular and balance rehabilitation, manual physical therapy, and graded exertional training based on individual patient presentations is needed to best manage patients referred for physical therapy with a concussion.
Footnotes
Dr Yorke and Dr Alsalaheen provided concept/idea/research design and data collection. All authors provided writing and data analysis. Dr Yorke provided project management and fund procurement. Dr Littleton provided participants and consultation (including review of manuscript before submission).
The authors thank the Acute Care, Education, Geriatrics, Home Health, Neurology, Orthopaedics, Pediatrics, Private Practice, and Sports sections for assisting in the dissemination of the survey to their members; the physical therapists who completed the survey; the Physical Therapy Department at the University of Michigan–Flint for financial support; and Jessica Smith, PT, DPT, Kayla Stockdale, BS, and Justin Diebold, BS, for assisting in the research on state concussion legislation.
The study was approved by the Institutional Review Board at the University of Michigan–Flint.
- Received January 5, 2015.
- Accepted November 22, 2015.
- © 2016 American Physical Therapy Association
References
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