Table 2.

Key research areas and priorities.

Area	Current State	Research Priorities
Manualized EAS interventions	Currently a few manualized interventions exist, but no comparison studies have been conducted.	Direct comparisons of interventions in randomized controlled trials including multi-site studies.
Dose–response relationships and frequency of treatment	The optimal dosage and frequency of EAS interventions is unknown.	Compare outcomes of standardized interventions across multiple dosing and frequency options.
Horse–human interaction	Limited understanding of mechanisms underlying how horse–human interactions contribute to therapeutic outcomes. Relative benefits of EAS interventions with mental-health-treatment components versus those without is unknown. Relative benefits of EAS interventions with mental-health-treatment components that use metaphor versus those that do not use metaphor is unknown. Relative benefits of EAS interventions with mounted activities versus those without is unknown.	Mechanism of action studies measuring human attachment, psychological flexibility, mindfulness, human–animal attachment, and sense of control, autonomy, and assertiveness. Parse the potential mechanism of biophilia. Mechanism of action studies measuring horse and human HRV, heartrate synchronization, oxytocin, and cortisol, as well as human brain activation. Compare outcomes of standardized interventions with and without a mental-health-treatment component. Compare outcomes of standardized interventions with a mental-health-treatment component and with and without the use of metaphor. Compare outcomes of standardized interventions with and without mounted activities.
Treatment engagement and therapeutic alliance with EASs and conventional interventions	Most evidence from the general AAI literature. Some evidence that veterans enjoy EASs and attrition may be less that with conventional interventions.	Direct comparisons of enrollment and attrition in EASs versus conventional treatments. Utilization of treatment engagement and therapeutic alliance scales. Qualitative studies of veteran EAS experience. Determine if physiologic or psychological measures correlate with treatment engagement and/or therapeutic alliance in EASs. Determine if human–horse attachment is correlated with treatment engagement and/or therapeutic alliance.
Transdiagnostic benefits and symptom reduction	Many studies suggest benefit, but rigorous studies are generally lacking. Limited evidence of long-term benefit.	Large randomized controlled trails. Determine if human–horse attachment correlates with treatment response. Determine if physiologic measures correlate with treatment response.
Potential adverse outcomes for human participants	Horse-related injuries, short-term emotional discomfort, and re-traumatization are risks of EASs. A few EAS studies of veterans have reported no adverse outcomes.	EAS interventions should have a response to adverse events plan. Studies should assess for, and report on, adverse outcomes.
Potential adverse outcomes for equine partners	Several studies suggest that EASs are not stressful for horses; however, more research is needed to confirm.	Horse and human physiologic measures, which are useful to disambiguate mechanisms of action, can also be used to evaluate equine stress in EASs. These include HRV, cortisol, and equine behavior scales.