Bifactor Model of the Sport Concussion Assessment Tool Symptom Checklist: Replication and Invariance Across Time in the CARE Consortium Sample

Abstract

Background: Identifying separate dimensions of concussion symptoms may inform a precision medicine approach to treatment. It was previously reported that a bifactor model identified distinct acute postconcussion symptom dimensions. Purpose: To replicate previous findings of a bifactor structure of concussion symptoms in the Concussion Assessment Research and Education (CARE) Consortium sample, examine measurement invariance from pre- to postinjury, and evaluate whether factors are associated with other clinical and biomarker measures. Study Design: Cohort study (Diagnosis); Level of evidence, 2. Methods: Collegiate athletes were prospectively evaluated using the Sport Concussion Assessment Tool–3 (SCAT-3) during preseason (N = 31,557); 2789 were followed at <6 hours and 24 to 48 hours after concussion. Item-level SCAT-3 ratings were analyzed using exploratory and confirmatory factor analyses. Bifactor and higher-order models were compared for their fit and interpretability. Measurement invariance tested the stability of the identified factor structure across time. The association between factors and criterion measures (clinical and blood-based markers of concussion severity, symptom duration) was evaluated. Results: The optimal structure for each time point was a 7-factor bifactor model: a General factor, on which all items loaded, and 6 specific factors—Vestibulo-ocular, Headache, Sensory, Fatigue, Cognitive, and Emotional. The model manifested strict invariance across the 2 postinjury time points but only configural invariance from baseline to postinjury. From <6 to 24-48 hours, some dimensions increased in severity (Sensory, Fatigue, Emotional), while others decreased (General, Headache, Vestibulo-ocular). The factors correlated with differing clinical and biomarker criterion measures and showed differing patterns of association with symptom duration at different time points. Conclusion: Bifactor modeling supported the predominant unidimensionality of concussion symptoms while revealing multidimensional properties, including a large dominant General factor and 6 independent factors: Headache, Vestibulo-ocular, Sensory, Cognitive, Fatigue, and Emotional. Unlike the widely used SCAT-3 symptom severity score, which declines gradually after injury, the bifactor model revealed separable symptom dimensions that have distinct trajectories in the acute postinjury period and different patterns of association with other markers of injury severity and outcome. Clinical Relevance: The SCAT-3 total score remains a valuable, robust index of overall concussion symptom severity, and the specific factors identified may inform management strategies. Because some symptom dimensions continue to worsen in the first 24 to 48 hours after injury (ie, Sensory, Fatigue, Emotional), routine follow-up in this time frame may be valuable to ensure that symptoms are managed effectively.

Factor Structure for the Sport Concussion Assessment Tool Symptom Scale in Adolescents After Concussion

“…Contrary to Brett et al who identified a headache factor (headache and pressure in head) and a sensory factor (sensitivity to light and sensitivity to noise), these 4 symptoms (headache, pressure in head, sensitivity to light, and sensitivity to noise) were all loaded on the Migrainous factor in the current investigation. In addition, the Vestibulo-Ocular factor (4 symptoms) and the Energy factor (5 symptoms) in the current investigation were more encompassing than the vestibulo-ocular factor (3 symptoms) and fatigue factor (2 symptoms) reported by Brett et al 13 It has been assumed that energy-related symptoms (eg, fatigue) are closely associated with the acute period after injury, during which physical and cognitive rest are recommended. 34 However, the emergence of the Energy factor as the largest contributor to variance (17%) in a sample of adolescents seen up to 30 days since the injury underscores the importance of using a graded and individually dosed rehabilitation approach throughout recovery and the importance of specifically inquiring about and clinically addressing these items.…”

“…It is noteworthy to mention that neck pain and trouble falling asleep did not meet the loading criteria on any of the identified factors in the model and therefore were not considered in the 5-factor model, which is consistent with what is previously reported in adults. 13 The failure of neck pain to meet the loading criteria is not surprising considering that neck pain may result from a co-occurring neck injury (eg, whiplash) as opposed to being directly attributable to concussion. 15,45 Similarly, trouble falling asleep did not meet the loading criteria on any of the identified factors that may be explained by the more stringent sleep query in the SCAT5 symptom checklist as opposed to other postconcussive symptom inventories previously used for factor analysis.…”

“…[13][14][15] However, concussion symptoms onset of emergence and aggregation of symptoms may be time dependent. 13 Therefore, the findings of previous work examining the factorability of concussion symptoms within 72 hours may not be generalizable to most individuals seen in a clinical setting. Another limitation of the aforementioned studies is the restriction of participants to adults only 13 and the lack of disaggregated results by age groups in studies that included mixed sample of adults and adolescents.…”

“…Studies examining the factor structure of SCAT3 symptoms in acutely concussed individuals evaluated within 72 hours of concussion. [13][14][15] However, concussion symptoms onset of emergence and aggregation of symptoms may be time dependent. 13 Therefore, the findings of previous work examining the factorability of concussion symptoms within 72 hours may not be generalizable to most individuals seen in a clinical setting.…”

Acute Physical and Mental Activity Influence on Concussion Recovery

“…In some cases, the clinicians performed the GSC with the athlete, and the research team only had access to the total score (total number of symptoms and symptom burden); thus, assessment of individual symptoms (e.g., dizziness, difficulty concentrating, etc.) could not be performed and symptom reporting can be confounded by numerous considerations (49,50). All participants herein were medically managed by the same athletic training and team physician staff using the same concussion management protocol; however, individual management practices and participant experiences/expectations could influence the outcomes of the study.…”