Animal-Assisted Intervention for Posttraumatic Stress Disorder


The treatments for patients with a psychological problem using animal has been commonly used. At the late eighteenth century, the first Animal-assisted therapy began in mental health institutions to increase socialization among patients (Serpell, 2015). Today, several health institutions have managed a lot of programs in the United States and reported involving animals in their services. One of the most popular target group for AAI is subjects who have experienced trauma, including those with posttraumatic stress disorder (PTSD; (Tedeschi, Fine, & Helgeson, 2010)).

AAI is usually defined as any treatment or intervention that includes an animal as part of it (Kruger & Serpell, 2010). It included targeted therapeutic interventions with animals (Animal-Assisted Therapy), less structured enrichment activities with animals (Animal-Assisted Activities), and the provision of trained animals to assist with daily life activities (Service or Assistance Animals). PTSD is an anxiety disorder that is characterized by symptoms related to intrusion, avoidance, negative alterations in cognition and mood, and alterations in arousal and reactivity (American Psychiatric Association, 2000).

The estimated number of patient is approximately 7.8% of the US population (Kessler, 1995) and this occurrence can make substantial work and burdens. It is a difficult disorder to treat, with dropout and non-response rates up to 50% in studies of empirically-supported treatments(Schottenbauer, Glass, Arnkoff, Tendick, & Gray, 2008).

The purpose of this paper is to present a comprehensive overview of the following researches on AAI for PTSD to show what impact AAI have had on the mental health of patients who have Posttraumatic Stress Disorder (PTSD).

Tracy J. Dietz, Evaluating Animal-Assisted Therapy in Group Treatment for Child Sexual Abuse

Kathleen Kemp, Equine Facilitated Therapy with Children and Adolescents Who Have Been Sexually Abused: A Program Evaluation Study

Liat Hamama, A preliminary Study of group intervention along with basic canine training among traumatized teenagers: A 3-month longitudinal study

Research Question & Hypothesis

Question: What impact have Animal-Assisted Intervention (AAI) had on the mental health of patients who have Posttraumatic Stress Disorder (PTSD)?

Null Hypothesis: Animal-Assisted Intervention is not related to the improvement of PTSD symptoms of young adults, including depression, anxiety.

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Characteristics of AAI for PTSD

the key factors of AAI in the studies were extracted and are summarized in Table 1 to describe the characteristics of AAI for PTSD.

Throughout the study, the different terminology used to identify AAI depending on the kind of animal participating in the study. Terms were varied across every study, such as animal-assisted therapy, equine-facilitated therapy, dog-assisted therapy and canine-assisted therapy.

The 2 of those studies included dogs as the therapy animal, while another study focused on horses. The dog-based interventions occurred in a treatment center and a school and another patient group treated in the riding center with horses.

Specified interventionists who facilitated the AAI sessions or therapists have presented for all studies. Format of the studies were group sessions, which varying a number of participants in each group, with only two of three studies reporting group size ranged from 6 to 10.

The duration of AAIs ranged from 7 to 12 weeks. 2 studies reported an exact duration; however, when only a range was reported, we used the midpoint of the range in descriptive calculations. The average duration of AAI was 9.5 weeks (range: 7*12, SD = 2.0) with 11.2 sessions (range: 9*12, SD = 1.2), each lasting 135.0 min (range: 90*180, SD = 63.6).

Methodological Evaluation

Key characteristics of the methods were listed and summarized with respect to each study’s sample size and characteristics, study design, and assessment type (Table 2) to evaluate study methodology and risk of bias.

Sample sizes of studies ranged from 9 to 153 participants, with two of the studies having a relatively small sample size (less than 30 subjects). The percentage of males ranged from none to 20%, with males making up 8.3% (16 of 192 participants) of the total sample across the studies. All studies were conducted with children and adolescent patients and the age of participants was reported as a range of them. Using the information provided by studies, the mean age of participants was 11.7 years. (range: 7-17, SD=5.99)

Each study has a different study design; a pre-post design, non-randomized control, and waitlist to treatment design. A “pre-post” study examines whether participants in an intervention improve or regress during the course of the intervention, and then attribute any such improvement or regression to the intervention. In psychotherapy research, a wait-list control group is a group of participants who do not receive the experimental treatment, but who are put on a waiting list to receive the intervention after the active treatment group does. Surveys were used for assessment for all studies and responses were self-report.

Outcomes of AAI for PTSD

Although the designs and assessments of the studies were varied, key outcomes were identified and categorized. Table 3 reports effect sizes and mean percent change from before to after AAI for the most commonly reported outcomes in quantitative studies.

To compare effect sizes across studies, Cohen’s d effect size was used for all studies which reported means and standard deviations. two different formulas has been calculated based on study design. For within-participant designs, effect size was calculated by dividing the difference of the means by the average standard deviation of both repeated measures(Lakens, 2013; Schottenbauer et al., 2008).

dwithin=MdiffSD1+SD22 (1)

For between-participants designs, the effect size was calculated using the recommended formula for pre-post-control group designs using the pooled pre-test standard deviation. (Morris, 2008)

dbetween=cp(Mpost,T-Mpre,T)-(Mpost,C-Mpre,C)SDpre (2)

Where, the pooled standard deviation is defined as:

SDpre=(nT-1)SDpre,T2+(nC-1)SDpre,C2nT+nC-2 (3)


cp=1-34(nT+nC-2)-1 (4)

Beck Depression Inventory (BDI)

The BDI measures levels of depression in adults and adolescents. All 21 items are measured on a 4 point Likert scale and higher scores represent more severe levels of depression.

Beck Anxiety Inventory (BAI)

BAI is a 21 item questionnaire measured on a four-point Likert scale indicating the severity of anxiety symptoms.

Child Behavior Checklist (CBCL)

The CBCL is a caregiver report for children and adolescents aged 6 – 18 years which measures maladaptive social, emotional and overt behaviors. Scores for internalized (covert, anxious-depressive behavioral symptoms) and externalized (overt, non-compliance, hyperactive, aggressive) scales were used within this study, along with the Total behavior scores.

Children’s Depression Inventory (CDI)

The CDI (Kovcs, 2003) was created from the Beck Depression Inventory with 21 items adjusted semantically for age appropriateness and another five items added to account for school and peer functioning. Total scores range from 0 to 54 with higher scores denoting depressive symptomatology.

Epidemiologic Studies Depression Scale (SCESD)

SCESD is a 10 item scale intended to measure the severity of depressive symptoms an individual experience. The items are rated by frequency on a 4-point scale, where higher scores reflect a higher risk for depression.

Trauma Symptom Checklist (TSCC)

The TSCC is a 54 item questionnaire developed using a large Australian normative sample. It is designed to assess post-trauma symptomatology in children and adolescents. TSCC is scored on a four-point Likert scale with higher scores depicting higher states of trauma. The TSCC includes six clinical scales: Depression, anxiety, post-traumatic stress, sexual concerns, dissociation, anger(Mackler 2012).

PTSD Symptoms

The PTSD Checklist-Civilian Version (PCL-C) which uses 17 items addressing the DSM-IV diagnostic criteria for PTSD, and the Trauma Symptom Checklist for Children (TSCC) were used to assess PTSD symptoms. Outcomes included reduced PTSD symptoms following AAI, compared to before the AAI. These changes were significant compared to the comparison condition in one study of 30 participants with horses (Kemp et al., 2013)


Four different instruments were used to assess depression; the Short Center for Epidemiologic Studies Depression Scale (SCESD), Beck Depression Inventory (BDI), Children’s Depression Inventory (CDI), and the Trauma Symptom Checklist for Children (TSCC). Outcomes included reduced depression following AAI, compared to before the AAI and after the comparison condition.


Only one survey instruments were used to assess anxiety, the Trauma Symptom Checklist for Children (TSCC). Outcomes in two studies included reduced anxiety following AAI, compared to before the AAI and to the comparison condition.


Although the Studies reviewed in this report have a relatively small population and one of studies did not have any controlled group which compares to the treated group, all data showed positive outcomes of AAI for patients who have PTSD, depression, and anxiety.

First, we could find that there was reduced depression after AAI. Even the effect size of Hamama study is less than 0.2, most of the studies showed that decrease of depression symptoms between pre- and post-AAI are statistically significant. Consequently, reductions in depression may be related to positive perceptions of animals.

PTSD symptom severity was also reduced after treating AAI. It is unclear whether there are specific symptoms that were targeted in AAI protocols, or whether there are specific symptoms that were most amenable to change from AAI. However, reductions in depression seem to be related to changes in the PTSD symptom of negative alterations in cognition and mood.

Consequently, we reject the null hypothesis and accept the alternative hypothesis even though some of the study result is still not statistically significant.


  • American Psychiatric Association. (2000). Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR). American Psychiatric Association.
  • Kessler, R. C. (1995). Posttraumatic Stress Disorder in the National Comorbidity Survey. Archives of General Psychiatry, Vol. 52, p. 1048.
  • Kovcs, M. (2003). Children’s Depression Inventory (CDI): Technical Manual Update.
  • Kruger, K. A., & Serpell, J. A. (2010). Animal-assisted interventions in mental health. Handbook on Animal-Assisted Therapy, pp. 33-48.
  • Lakens, D. (2013). Calculating and reporting effect sizes to facilitate cumulative science: a practical primer for t-tests and ANOVAs. Frontiers in Psychology, Vol. 4.
  • Morris, S. B. (2008). Estimating Effect Sizes From Pretest-Posttest-Control Group Designs. Organizational Research Methods, Vol. 11, pp. 364-386.
  • Mackler, K. (2012). Review of the Trauma Symptom Checklist for Children By: Briere, John, Mental Measurements Yearbook, 15.
  • Schottenbauer, M. A., Glass, C. R., Arnkoff, D. B., Tendick, V., & Gray, S. H. (2008). Nonresponse and dropout rates in outcome studies on PTSD: review and methodological considerations. Psychiatry, 71(2), 134-168.
  • Serpell, J. A. (2015). Animal-Assisted Interventions in Historical Perspective. Handbook on Animal-Assisted Therapy, pp. 11-19.
  • Tedeschi, P., Fine, A. H., & Helgeson, J. I. (2010). Assistance animals. Handbook on Animal-Assisted Therapy, pp. 421-438.

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Animal-Assisted Intervention for Posttraumatic Stress Disorder. (2019, Dec 18). Retrieved from

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