ANTHROZOÖS VOLUME 20, ISSUE 2 REPRINTS AVAILABLE PHOTOCOPYING ISAZ 2007 PP 167 180 DIRECTLY FROM PERMITTED PRINTED IN THE UK THE PUBLISHERS BY LICENSE ONLY Do Anmal-Asssted Actvtes Effectvely Treat Depresson? A Meta-Analyss Megan A. Souter and Mchelle D. Mller Department of Psychology, Northern Arzona Unversty, USA Address for correspondence: Dr Mchelle Mller, Department of Psychology, Northern Arzona Unversty, Flagstaff, AZ 86011-5106, USA. E-mal: Mchelle.Mller@nau.edu ABSTRACT We conducted a meta-analyss to determne the effectveness of anmal-asssted actvtes (AAA) and anmal-asssted therapy (AAT) for reducng depressve symptoms n humans. To be ncluded n the meta-analyss, studes had to demonstrate random assgnment, nclude a comparson/control group, use AAA or AAT, use a self-report measure of depresson, and report suffcent nformaton to calculate effect szes, a statstcal standardzaton of the strength of a treatment effect. Fve studes were dentfed for analyss. The aggregate effect sze for these studes was of medum magntude and statstcally sgnfcant, ndcatng that AAA/AAT are assocated wth fewer depressve symptoms. Ths analyss revealed gaps n the research on AAA/AAT, whch we attempted to dentfy n order to better understand the factors that make AAA and AAT effectve at reducng depresson. Keywords: anmal-asssted actvtes, anmal-asssted therapy, depresson, meta-analyss, pet therapy Anmal-asssted actvtes (AAA) and anmal-asssted therapy (AAT) are becomng ncreasngly common as therapeutc nterventons n health care facltes such as nursng homes and hosptals. Varous terms have been used to descrbe AAA and AAT such as pet therapy, pet-facltated therapy, pet-asssted therapy, anmal-facltated therapy, and anmal vstaton (Connor and Mller 2000). The Delta Socety, a leadng nternatonal, not-for-proft organzaton that provdes tranng for AAA and AAT practce, categorzes these types of nterventons under the preferred terms of anmalasssted actvtes (AAA) and anmal-asssted therapy (AAT; Standards of Practce 1996). The followng are formal defntons of AAA and AAT: AAA provde opportuntes for motvatonal, educatonal, recreatonal, and/or therapeutc benefts to enhance qualty of lfe. AAA are delvered n a varety of envronments by specally traned professonals, paraprofessonals, and/or volunteers, n assocaton wth anmals that meet specfc crtera ( Standards of Practce 1996). 167 Anthrozoös DOI: 10.2752/175303707X207954
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? AAT s a goal-drected nterventon n whch an anmal that meets specfc crtera s an ntegral part of the treatment process. AAT s drected and/or delvered by a health/human servce provder workng wthn the scope of practce of hs/her professon. AAT s desgned to promote mprovement n human physcal, socal, emotonal, and/or cogntve functonng. AAT s provded n a varety of settngs and may be group or ndvdual n nature. Ths process s documented and evaluated. 168 Anthrozoös Although by defnton AAA and AAT are dstngushable, n actual practce the two are not clearly dfferentated and at tmes may overlap. In most stuatons, AAA and AAT are provded to ndvduals or groups wth the ad of volunteers and/or health care practtoners (Barba 1995). The ntenton of these actvtes s to promote health and well-beng among those ndvduals who are affected by a varety of ssues, ncludng depresson, autsm, emotonal dsorders, Alzhemer s, and physcal dsabltes. These types of human anmal nteractons can be experenced n a varety of settngs such as hosptals, nursng homes, hospces, rehabltaton facltes, oncology unts, acute and crtcal care unts, psychatrc facltes, psychotherapy, and prsons (Connor and Mller 2000). A number of researchers have attempted to show that AAA and/or AAT postvely affect a wde array of outcome varables such as blood pressure, heart rate, exercse level, stress, socal nteracton, anxety, lonelness, and depresson. However, these research studes have produced mxed results regardng the effectveness of AAA and AAT, and the pcture s further clouded by the fact that these studes vary along such mportant dmensons as settng, patent populaton, type of anmal, duraton of vsts, and frequency of anmal nteractons. We conducted the present study to determne whether exstng research supports the effectveness of AAA/AAT n therapeutc settngs. In such settngs, AAA and AAT may produce benefts related to health and qualty of lfe or wellbeng. Some of the clamed physologcal benefts of these human anmal nteractons nclude decreased blood pressure, ncreased actvty and moblty, decreased heart rate, mproved recovery rate, better copng wth llness, and general benefts from physcal contact or touch (Delta Socety n.d.; McCulloch 1983; Boldt and Dellman-Jenkns 1992). Potental psychologcal benefts nclude ncreased empathy, relaxaton, mproved self-esteem and acceptance, stress and anxety reducton, realty orentaton, nurturng sklls, mental stmulaton, decreased lonelness, ncreased postve affect, and opportuntes to remnsce about past experences wth pets or lfe experences n general (Delta Socety n.d.; McCulloch 1983; Boldt and Dellman-Jenkns 1992; Barba 1995; Brasc 1998). Does AAT/AAA actually delver these potental benefts? Some studes seem to offer evdence to ths effect, reportng mproved socal nteracton n resdents of nsttutonal care facltes (Francs, Turner and Johnson 1985; Wnkler et al. 1989; Fck 1992; Perelle and Granvlle 1993; Batson et al. 1998). Postve effects have also been reported for patent mood (Crowley-Robnson, Fenwck and Blackshaw 1996; Jessen, Cardello and Baun 1996). Although such results are promsng, much of the research lacks the methodologcal leverage to make clear nferences about AAA/AAT effects. One common lmtaton s the absence of random assgnment (Norrs 1983; Hagman 1997). Some studes also fal to nclude control groups (Wnkler et al. 1989; Vaughan 1990; Perelle and Granvlle 1993). For those studes usng observatonal methods, observer bas and blndng are also ssues to consder (Jendro, Watson and Qugley 1984; Perelle and Granvlle 1993). Some of the research ndcates that AAA and AAT have lttle mpact. For example, one study demonstrated no sgnfcant dfferences between a pet therapy group and an exercse control group on an observatonal scale assessng self-care functonng, dsorented behavor, depressed or anxous mood, rrtable behavor, or wthdrawn behavor (Zsselman et al. 1996). Another study ndcated no benefcal effects of AAA for psychologcal or functonal varables; however, partcpants showed sgnfcantly more purposeful behavor (.e., physcal movements/gestures and/or verbal expressons exhbted wth the ntent of havng needs or wants met, p. 419) whle n the AAA sesson (Jendro, Watson and Qugley 1984). In addton, other studes report mxed fndngs n regard to the
Souter and Mller effectveness of AAA and AAT (Harrs, Rnehart and Gerstman 1993; Batson et al. 1998). The varablty n the desgns and types of programs beng mplemented makes t dffcult to determne whch programs or whch components of programs could be the most effectve. Thus, a narratve revew cannot clearly elucdate whether or not AAA or AAT s useful. Meta-analyss, on the other hand, offers a more systematc way to summarze and evaluate the dverse lterature on the effectveness of AAA and AAT. Meta-analyss s a procedure used to summarze the quanttatve results of emprcal research studes (Lpsey and Wlson 2001). The process of executng a meta-analyss nvolves gatherng comparable emprcal research on the topc of nterest and codng and analyzng study characterstcs and statstcal fndngs that are reported n ndvdual studes (Lpsey and Wlson 2001). Statstcal procedures are then performed to quantfy results across studes n order to summarze the research fndng or queston of nterest. In selectng studes for our meta-analyss, we chose to focus on those that used depresson or depressed mood as an outcome varable. Our reasonng was as follows: Depresson s a serous condton that affects many people (approxmately 19 mllon adults n the US alone; Natonal Insttute of Mental Health [NIMH] n.d.) and has dsablng effects (Natonal Insttute of Health [NIH] 1992). Depresson can also ntensfy the effects of co-exstng physcal llnesses, an mportant consderaton gven that t often co-exsts wth other serous dseases such as heart dsease, stroke, cancer, and dabetes (NIMH n.d.). A recent NIMH study (Pratt et al. 1996) suggested that an ndvdual wth depresson has an ncreased rsk for havng a heart attack n the future. Accordng to the Global Burden of Dsease study n 1990, depresson s predcted to be the second cause of dsease burden n the naton, second to schemc heart dsease for 2020 (Murray and Lopez 1996). Depresson s a partcularly pressng concern among older adults, especally nsttutonalzed older adults, wth prevalence rates of major and mnor depresson among older adults n nursng homes reachng 15% to 25% (NIH 1992). Methods Lterature Search The studes for ths meta-analyss were located by searchng the followng databases: PsychINFO, ERIC, Socal Servces, Socologcal Abstracts, Academc Search Premer, NIMH, Health and Wellness Resource Center, PubMed, Agrcola, Melvyl Catalog, Cnahl, Health Source-nursng/academc edton, Kluwer, Medlne, Project Muse, Scence Drect, Cochrane Database of Systematc Revews, and Dssertaton Abstracts Internatonal. Key terms used n searches ncluded pets, pet therapy, companon anmal, pets and hosptals, pets and human health, pet-facltated therapy, pet-facltated therapy and depresson, pet therapy and depresson, bondng-human-pet and aged, bondnghuman-pet and nursng homes, bondng-human-pet and psychotherapy, pets and elderly, anmals and therapeutc use, human-pet and bondng, human anmal relatonshps, pets-socal aspects, anmal-asssted actvtes, anmal-asssted therapy, and anmal therapy. The journal Socety and Anmals was also searched for artcles related to AAA and AAT. Webstes on AAA and AAT and webstes of unverstes wth programs focusng on human anmal relatonshp research were revewed for possble research artcles, ncludng www.deltasocety.org, www.dog-play.com/therapy.html, www.censhare.umn.edu, www.therapyanmals.org, www.vetmed.ucdavs.edu/ccab/paws.htm, www.latham.org, www.tufts.edu/vet/cfa/ndex.html, and www.vet.upenn.edu/cas. Artcles were restrcted to those publshed n Englsh; however, there were no restrctons for year of publcaton. If abstracts of the studes were avalable, they were read, and the studes were retreved f they appeared to be related to the research queston of focus. The reference lsts of the collected papers were revewed, and artcles that appeared to meet the metaanalyss ncluson crtera were retreved and examned. Because ths meta-analyss focused on AAA and/or AAT, studes on pet ownershp were excluded. Artcles that appeared to concentrate on depresson and AAA and/or AAT were searched for and examned. After excludng artcles on pet ownershp, the lterature search led to 165 artcles 169 Anthrozoös
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? that were revewed to determne f they would be ncluded n the meta-analyss (not all of the 165 artcles examned depresson). Of the 165 artcles, 105 were summares/revews, theoretcal papers, edtorals, methodologcal papers, and anecdotal papers, whch dd not nclude data that could be analyzed. Of the 60 remanng studes, approxmately half dd not nclude a measure of depresson and only fve met the selecton crtera set for ths meta-analyss (Brckel 1984; Struckus 1989; McVarsh 1994; Wall 1994; Panzer-Koplow 2000). Selecton Crtera In order to be ncluded n the meta-analyss, each study was requred to meet several crtera. These crtera were random assgnment, ncluson of a control group, exposure to some form of AAA or AAT, and a measure of depressve symptoms. Restrctons for the depresson measures were that they had to be a self-report questonnare, ether flled out by the partcpant or verbally admnstered by the researcher or a volunteer. More mportantly, all studes had to report results n suffcent detal for us to calculate effect szes. The fve studes that met the selecton crtera for ths meta-analyss conssted of four dssertatons and one conference paper (Brckel 1984; Struckus 1989; McVarsh 1994; Wall 1994; Panzer- Koplow 2000). Two addtonal studes were retreved that met all crtera except for provdng suffcent data to calculate effect szes. Attempts were made to contact the authors of these studes by callng departments of the schools where they conducted ther research. The dssertaton charperson of one of the authors was also reached to nqure about contact nformaton of the author. These attempts dd not result n suffcent nformaton to contact ether author; therefore, these studes were not ncluded n the meta-analyss. Varable-Depressve Symptom Instruments The studes ncluded n the meta-analyss used the followng valdated self-report measures of depressve symptoms: Zung Self-Ratng Depresson Scale (Zung 1965; Zung 1974), the Beck Depresson Inventory (BDI; Beck et al. 1961), the Beck Depresson Inventory, II (BDI-II; Beck, Steer and Brown 1996), the Geratrc Depresson Scale (GDS; Brnk et al. 1982; Yesavage et al. 1983), and the NIMH Mood Scales-Elderly Depressed factor (MS-E; Raskn and Crook 1988). Reported posttest means and standard devatons for the chosen depresson measures were used to calculate an effect sze statstc for each of the fve studes. The posttest means and standard devatons ncluded those from both treatment and control groups. The sample sze of each group was also used n the calculaton. Due to varatons n the operatonalzaton of depresson across studes, the standardzed mean dfference between the treatment and control groups of each study was the effect sze statstc chosen for ths meta-analyss. 170 Anthrozoös Study Characterstcs In order to qualtatvely descrbe our studes, we noted the followng characterstcs of each one: (a) type of publcaton; (b) publcaton year; (c) role of expermenter n treatment; (d) dscplne of research; (e) sample source (e.g., nursng home, hosptal, psychatrc hosptal, hosptal-based nursng home care unt, VA medcal hosptal, day care center, rehabltaton unt, homebound); (f) mean age of sample at begnnng of nterventon; (g) predomnant sex of sample (.e., proporton of females n sample); (h) predomnant ethncty; () specal characterstcs of partcpants (e.g., psychatrc, dementa, dagnostcs); (j) type of assgnment to condtons; (k) whether or not equvalence of groups was tested at pretest; (l) pretest dfferences, f tested; (m) total sample sze at begnnng of study; (n) treatment group sample sze; (o) control groups sample szes; (p) type of treatment (e.g., anmal-asssted therapy, anmal-asssted actvty, mascot or resdent anmal, lve-n anmals n ndvdual rooms, anmal-asssted actvty and current events dscusson); (q) type of anmal nteracton for treatment groups (e.g., ndvdual or group); (r) duraton (n mnutes) of each vst for treatment group and control groups; (s) number of total vsts for treatment group and control groups; (t) duraton of treatment n weeks (.e., length of tme between pre and posttestng) for
Souter and Mller treatment group and control groups; (u) ntensty of treatment (e.g., pettng, groomng, walkng); (v) type of nterventon for control groups (e.g., person vst, person and stuffed anmal vst, person and photo of anmals, recreatonal actvty, no actvty or treatment, conventonal therapy, exercse, current events dscusson); (w) delvery of nterventon for treatment group and control groups (e.g., faclty staff, researcher, volunteers or owners of pets, veternaran or veternaran techncan, not reported); (x) number of volunteers per partcpant for anmal-asssted actvtes; (y) type of anmal; (z) survey desgn for varable of nterest; (aa) dependent varable (e.g., depresson, anxety, stress, lonelness, affect, mood) and nstrument used to measure the dependent varable; (bb) other dependent varables; and (cc) addtonal types of treatment groups. Gven the small number of studes n the analyss, we dd not examne how each of these characterstcs nfluenced the outcome of treatment or whether any nfluence was statstcally sgnfcant. Effect Sze Calculatons We used the formulas for the standardzed mean dfference descrbed by Lpsey and Wlson (2001) to calculate effect szes (also known as Cohen s d). The standardzed mean dfference nvolves calculatng the pooled standard devaton, the based effect sze, the corrected effect sze, the standard error of the effect sze, and the nverse varance weght (see formulas 1 5 n Table 1). Ths effect sze statstc was used because t allowed us to compare the effects of AAA and/or AAT on depresson among control and treatment groups to determne f AAA and AAT are effectve as therapeutc nterventons. The standardzed mean dfference effect sze formulas were most approprate to assess ths because they are used to compare the means of two groups on a dependent varable when the dependent varable s contnuous and not operatonalzed n the same manner across research studes (Lpsey and Wlson 2001). The effect sze formula ncludes subtractng group means for the numerator and estmatng the pooled standard devaton for the denomnator (Lpsey and Wlson 2001). When comparng treatment and control groups, a postve effect sze s an ndcaton that the nterventon was effectve. For stuatons when hgher scores on a dependent measure ndcate progress, t s approprate to subtract the control group mean from the treatment group mean when calculatng the numerator of the effect sze formula. Because lower scores rather than hgher scores ndcated progress (e.g., less depressed) on all of the dependent measures examned n the present meta-analyss, the order of subtracton for the numerator was reversed (.e., the treatment group mean was subtracted from the control group mean) (Lpsey and Wlson 2001). By makng ths change n the subtracton order for the numerator, a postve effect sze remaned as an ndcator that the nterventon was effectve. All studes reported the requred nformaton n order to calculate the effect sze; however, for one study (Panzer-Koplow 2000) the pretest standard devatons were used as an estmate of the pooled standard devaton because posttest standard devatons were not reported. After the effect sze was calculated, t was used to compute a corrected or unbased effect sze estmate (Lpsey and Wlson 2001). A corrected effect sze s necessary to calculate because the orgnal effect sze value tends to be upwardly based when estmated on small sample szes (Hedges 1981). In addton to calculatng the corrected effect sze estmate, the standard error of the effect sze and the nverse varance weght are calculated (Lpsey and Wlson 2001). These statstcs are computed n order to obtan a weght for each effect sze. Because the varous effect szes are based on a range of sample szes, weghts are used to represent the precson of each effect sze (Lpsey and Wlson 2001). These weghts are derved from the standard error of the effect sze by calculatng the nverse of the squared standard error value. Ths value s termed the nverse varance weght. The analyss of the meta-analytc data nvolved usng the corrected effect szes, standard errors of the effect szes, and nverse varance weghts of the effect szes to analyze the effect sze mean and dstrbuton (see formulas 6 10 n Table 1). The effect sze mean was found by weghtng each 171 Anthrozoös
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? Table 1. Equatons used n the meta-analyss. Statstc Equaton 1. Pooled standard devaton 2. Based effect sze s = p ES = sm 2 (n 1) s + (n 1) s G1 G1 G2 (n G1 1) + (n G2 1) X G1 XG2 s p 2 G2 3. Corrected effect sze ES = 1 sm 3 4N 9 ES sm 4. Standard error of the effect sze SE = sm n + n G1 G2 n n G1 G2 + (ES sm) 2 2(n + n ) G1 G2 5. Inverse varance weght 6. Weghted mean effect sze w = 1 sm 2 SE sm ( W ES ) ES = W 2n n (n + n ) G1 G2 G1 G2 = 2(n + n ) + n n (ES ) 2 2 G1 G2 G1 G2 sm 7. Standard error of the mean effect sze SE = ES 1 W 8. Confdence ntervals around the mean effect sze 9. z-test 10. Test for homogenety ES = ES z (SE ) L (1 ) ES ES = ES + z (SE ) L U (1 ) ES z = ES SE ES 2 ( W ES ) Q = ( W ES ) W 2 11. Method of moments estmate for random varance component v = Q (k 1) W / W) 2 W ( 172 Anthrozoös 12. Percentage of total varaton across studes due to heterogenety 13. Fal-safe N 2 (Q df) I = 100 Q k O = k ES k ES c 1
Souter and Mller Table 2. Study descrptons and fndngs. Study Characterstc Descrpton Brckel (1984) Partcpants Total of 15 partcpants from a nursng home unt n a hosptal Condtons/Groups Anmal-Asssted Actvty Sesson Self-Report Measure Examned n Meta-Analyss Conventonal therapy (n = 5); Pet-facltated psychotherapy (n = 5); No-treatment control group (n = 5), no actvty 8 sessons over a 4-week perod; Each sesson approxmately 67.5 mnutes; Dog Zung Self-Ratng Depresson Scale McVarsh (1994) Partcpants Total of 74 partcpants from two psychatrc hosptals Condtons/Groups Anmal-Asssted Actvty Sesson Self-Report Measure Examned n Meta-Analyss Pet-facltated therapy group (n = 24); Anmal photograph group (n = 26); Control group (n = 24), no actvty One 40-mnute group vst; Dogs and cats Beck Depresson Inventory Panzer-Koplow Partcpants Total of 35 partcpants from a nursng home (2000) Condtons/Groups Anmal-Asssted Actvty Sesson Self-Report Measure Examned n Meta-Analyss Anmal-asssted therapy group (n = 15); Control group (n = 19), no actvty One ndvdual vst per week, lastng 15 mnutes, over a ten-week perod; Dog Beck Depresson Inventory II Struckus (1989) Partcpants Total of 50 partcpants from a nursng home Condtons/Groups Anmal-Asssted Actvty Sesson Self-Report Measure Examned n Meta-Analyss Anmal vstaton group (n = 25); Comparson group (n = 25), alternatve recreatonal actvty (.e., sng-alongs, readng aloud) 24 ndvdual vsts over a 12-week perod, wth each vst lastng approxmately 20 mnutes; Dog Geratrc Depresson Scale II Wall (1994) Partcpants Total of 80 partcpants from nursng home Condtons/Groups Anmal-Asssted Actvty Sesson Self-Report Measure Examned n Meta-Analyss Dog wth vstor (n = 20); Vstor wth a stuffed anmal (n = 20); Vstor alone (n = 20); No treatment control condton (n = 20), no actvty 3 ndvdual vsts over a two and a half week perod, wth each vst lastng approxmately 8 mnutes; Dog NIMH Mood Scales - Elderly (Depressed Factor) effect sze by ts nverse varance weght, summng these values, and dvdng by the sum of weghts (Lpsey and Wlson 2001). The standard error of the mean was also calculated. Confdence ntervals for the mean effect sze were found usng the standard error of the mean effect sze and a crtcal z-value. To test the sgnfcance of the mean effect sze, a z-test was computed. The effect sze dstrbuton was also tested for homogenety usng the Q statstc. 173 Anthrozoös
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? Results Study Characterstcs All fve chosen studes were conducted n the Unted States, and publshed between 1984 and 2000 (see Table 2 for a bref descrpton of each study). The studes took place n varous nsttutonal settngs ncludng a hosptal-based nursng home care unt, a psychatrc hosptal, and nursng homes. The mean age of ndvduals partcpatng n these studes ranged from 47 to 85. The majorty of these studes ncluded females (50% to 95%), wth the excepton of one study, whch ncluded only males (Brckel 1984). The predomnant ethncty of partcpants n these studes was Caucasan (.e., greater than 60% were Caucasan). The sample sze for treatment groups ranged from 5 to 25. For control groups, the sample sze also ranged from 5 to 25. For the studes that had more than one comparson group, the comparson group whose nterventon ncluded no treatment or actvty was chosen to be compared wth the treatment group for the meta-analyss. However, the comparson group for one of the studes n the meta-analyss engaged n a regularly scheduled recreatonal actvty (Struckus 1989). The type of treatment for four of the fve studes nvolved AAA or pet vstatons. One study used AAT as the nterventon. All anmal nteractons nvolved ndvdual vsts wth the excepton of one study usng group vsts (McVarsh 1994). The duraton n mnutes of each vst for treatment groups among the fve studes ranged on average from 8 mnutes to 67.5 mnutes. The number of total vsts for treatment groups ranged from one vst to 24 vsts. The duraton of treatment n weeks (length of tme between pretest and posttest) ranged from 0.71 weeks to 12 weeks. The type of anmal partcpatng n the nterventon was a dog for all studes. The study facltatng group vsts also ncluded a cat as part of the anmal nterventon (McVarsh 1994). Four out of the fve studes reported a sgnfcant reducton n depresson for the anmal nterventon groups from pre to posttest. The Panzer-Koplow (2000) study found that the control group experenced a reducton n depressve symptoms from pre to posttest; however, ths dfference was not sgnfcant. Mean Effect Szes An alpha level of 0.05 was used for all statstcal tests. Number of partcpants, means, and standard devatons for both treatment and comparson/control groups of each study were used n the calculatons (see Table 3). For each study, usng the standardzed mean dfference formulas, a pooled standard devaton, a based effect sze, a corrected effect sze, a standard error, a varance, and an nverse varance weght were calculated (see Table 4). The calculated effect szes were all statstcally ndependent. Fgure 1 dsplays the dstrbuton of effect szes n a forest plot generated wth Stata 8.2 (Stata Corp., College Staton, TX). Data were analyzed usng a random effects model. 1 The random varance component was 0.30. The random effects weghted mean effect sze was 0.61, wth a standard error of 0.30. The 95% confdence nterval for the mean effect sze was 0.03 to 1.19. A z-test showed that the mean effect sze for the sample of studes was statstcally sgnfcant, z = 2.05, p 0.05. Ths fndng supported the hypothess that AAA and AAT are effectve at allevatng depresson. Accordng to Cohen (1988), a standardzed mean dfference effect sze of 0.50 s consdered a medum effect sze, and 0.80 s consdered large. The mean effect sze found n ths meta-analyss falls between these two means and s closer to a medum mean effect sze. 174 Anthrozoös Homogenety To test the homogenety of the dstrbuton of effect szes, a Q statstc was computed and was found to be sgnfcant, Q (4) = 13.61, p 0.05, therefore rejectng the null hypothess of homogenety and determnng that the dstrbuton of effect szes was heterogeneous. In addton to the Q statstc, another statstcal approach was used to quantfy the effect of heterogenety. I 2 was calculated to determne the percentage of total varaton across studes that was due to heterogenety rather
Souter and Mller Table 3. Mean depresson scores and standard devatons for meta-analyss studes. Control/Comparson Treatment Study M SD n M SD n Brckel (1984) 60.60 5.90 5 56.00 6.10 5 McVarsh (1994) 38.40 5.71 24 24.34 12.79 24 Panzer-Koplow (2000) 7.05 7.36 19 9.33 6.57 15 Struckus (1989) 13.50 5.80 25 9.40 4.30 25 Wall (1994) 1.70 0.85 20 1.35 0.54 20 Table 4. Standardzed mean dfference calculatons for meta-analyss studes. Study sp ESsm ES sm SEsm vsm wsm Brckel (1984) 6.00 0.77 0.69 0.65 0.42 2.36 McVarsh (1994) 9.90 1.42 1.40 0.32 0.10 9.65 Panzer-Koplow (2000) 7.03-0.32-0.32 0.35 0.12 8.28 Struckus (1989) 5.11 0.80 0.79 0.29 0.09 11.59 Wall (1994) 0.71 0.49 0.48 0.32 0.10 9.72 Note. sp = pooled standard devaton of the standardzed mean dfference effect sze; ESsm = based standardzed mean dfference effect sze; ES sm = corrected or unbased standardzed mean dfference effect sze; SEsm = standard error of the standardzed mean dfference effect sze; vsm = varance of the standardzed mean dfference effect sze; wsm = nverse varance weght of the standardzed mean dfference effect sze. Accordng to Cohen (1988), an ES sm 0.20 s small, an ES sm = 0.50 s medum, and an ES sm 0.80 s large. Study Mean Dfference (d) (95% CI) Brckel 0.69 (-0.61, 1.99) McVarsh 1.40 (0.76, 2.03) Panzer-Koplow -0.32 (-1.00, 0.36) Struckus 0.79 (0.21, 1.37) Wall 0.48 (-0.15, 1.11) Overall 0.61 (0.03, 1.19) -2-1 0 1 2 Mean Dfference (d) Fgure 1. Forest plot of corrected standardzed mean dfference effect szes for depressve symptoms followng anmal-asssted actvtes/anmal-asssted therapy. Postve dfference scores reflect lower depressve symptoms n the therapy group. Box areas are proportonal to the sample sze of each study. than chance and was found to be 70.61% (Hggns et al. 2003). Due to the Panzer-Koplow study havng a corrected or unbased standardzed mean dfference effect sze of 0.32, whch was n the opposte drecton of the other studes, statstcs were recalculated excludng the data from the Panzer-Koplow (2000) study. The random varance component was 0.05. The random effects weghted mean effect sze was 0.87 wth a standard error of 0.21. The 95% confdence nterval for 175 Anthrozoös
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? the mean effect sze was 0.45 to 1.29. A z-test showed that the mean effect sze for the sample of studes was statstcally sgnfcant, z = 4.05, p 0.05. A Q statstc was recalculated excludng the Panzer-Koplow data to examne the heterogenety of the fve studes compared wth the four studes. A Q statstc was computed for the four studes and was not sgnfcant, Q (3) = 4.29, p > 0.05, therefore falng to reject the null hypothess of homogenety. Fgure 2 dsplays the dstrbuton of effect szes n a forest plot generated wth Stata 8.2 (Stata Corp., College Staton, TX). Heterogenety was no longer sgnfcant when excludng the Panzer-Koplow study. Study Mean Dfference (d) (95% CI) Brckel 0.69 (-0.61, 1.99) McVarsh 1.40 (0.76, 2.03) Struckus 0.79 (0.21, 1.37) Wall 0.48 (-0.15, 1.11) Overall 0.87 (0.45, 1.28) -2-1 0 1 2 Mean Dfference (d) Fgure 2. Forest plot of corrected standardzed mean dfference effect szes for depressve symptoms followng anmal-asssted actvtes/anmal-asssted therapy wth the Panzer-Koplow (2000) study excluded. Postve dfference scores reflect lower depressve symptoms n the therapy group. Box areas are proportonal to the sample sze of each study. Fal-Safe N Calculatons To determne the nfluence of unpublshed studes on ths meta-analyss (a.k.a., the fle drawer problem), the fal-safe N was calculated. The fal-safe N, a statstc developed by Rosenthal and later adapted to the standardzed mean dfference effect sze by Orwn, estmates the number of unpublshed studes wth nonsgnfcant fndngs that would decrease the cumulated effect of the studes to nonsgnfcant (Rosenthal 1979; Orwn 1983; Lpsey and Wlson 2001). Crteron effect sze levels were set at 0.50, a medum standardzed mean dfference effect sze accordng to Cohen, and 0.20, a small effect sze accordng to Cohen (1988). For the crteron effect sze level of 0.50, one unpublshed study wth a zero effect sze would be needed. For the crteron level of 0.20, the number of unpublshed studes wth a zero effect would be ten. 176 Anthrozoös Dscusson The results of our meta-analyss support the effectveness of AAA, and n one case, AAT, as treatments for depresson. Although the number of chosen studes was small, taken together, the results of these studes ndcate that exposure to AAA/AAT produces sgnfcant mprovement n depresson, as measured wth a range of well-accepted nstruments. Furthermore, these mprovements are unlkely to have resulted from artfacts n study desgn, as we ncluded only studes that met certan desgn standards, most notably the ncluson of a control group. By combnng the results across a number of studes, our meta-analyss makes a new contrbuton to what s known about the therapeutc effectveness of AAA/AAT. The present study also establshes what we can expect n terms of how much mprovement patents wll experence as a result of AAA/AAT. By standardzng across the results of a number of studes, we can place the lkely effect sze of AAA/AAT n the medum range, whch Cohen (1988)
Souter and Mller characterzes as a dfference between groups that s not large enough to be grossly obvous, but s large enough to be notceable to the casual observer. In other words, although patents undergong AAA/AAT are unlkely to experence a dramatc decrease n depresson, they wll lkely experence a notceable degree of relef. By consderng effect szes, our study provdes evdence to endorse not only the statstcal sgnfcance of anmal therapes, but ther practcal sgnfcance, as well. Although the dstrbuton of the fve effect szes was found to be heterogeneous, t s lkely that the heterogenety was due to extraneous varables n the Panzer-Koplow (2000) study. In the Panzer- Koplow study, partcpants n the control group showed a greater reducton n depressve symptoms than the anmal-asssted therapy group. There are possble explanatons for ths fndng. Partcpants reported that the double negatve wordng on the BDI-II was confusng. Toward the end of the nterventon, a caged brd and dog were brought to the faclty. It s possble that these extraneous varables could have affected the outcomes n ths study, especally snce the brd and dog were ntroduced to the faclty a few weeks before the post-tests were admnstered. These ssues are unque to the Panzer-Koplow study. When excludng the Panzer-Koplow study and recalculatng the heterogenety, the studes appear more homogenous. A further contrbuton of our meta-analyss s to hghlght the desgn shortcomngs assocated wth studes of AAA/AAT. Although we consdered a large number of studes for ncluson n the analyss, only a very small proporton met our (admttedly hgh) standards of research desgn. Many of the studes we consdered faled to randomly assgn partcpants to control and treatment groups. Some also desgned pretest/posttest studes n whch partcpants were exposed to AAA before the pretest, thereby obscurng whether or not the anmal nterventon was the factor leadng to a reducton n depresson. Our systematc survey of the lterature revealed several crucal gaps. Although we chose to focus on depresson as an outcome measure, we beleve that t would be equally mportant to research the effect of AAA/AAT on physologcal measures (e.g., heart rate, blood pressure), yet few studes ncorporate such measures. Blood pressure would be partcularly mportant to measure because t s a health rsk marker (e.g., hgh blood pressure s consdered a major rsk factor for cardovascular dsease; NIH n.d.). Of the 165 studes we revewed, only nne ncorporated physologcal measures. Of these nne studes, fve dd not measure depresson, one was a case hstory, two dd not use random assgnment, and one study s author could not be contacted to gan further statstcal nformaton. A number of pet ownershp versus non-pet ownershp studes assess physologcal measures; however, ths s much less common among studes examnng AAA/AAT. Another gap n the lterature s the lack of research specfcally addressng the degree to whch the postve effects of AAA/AAT are attrbutable to contact wth the human beng facltatng the anmal vst. Some studes do nclude human contact-only groups to compare wth anmal nteracton and control groups; however, n the present meta-analyss only one study ncluded a person vst only group to be compared wth the AAA group (Wall 1994), precludng us from nvestgatng ths factor n a systematc way. In most of the studes ncluded n the meta-analyss, ether the nvestgator or the volunteer anmal handler facltated the nterventon and collected the data, wth the excepton of one study (Struckus 1989) n whch the nterventon and data collecton was facltated by ndvduals naïve to the research component of the study. Therefore, expermenter bas s a possble flaw of the studes and could have nflated the effect szes. However, because the data used n the meta-analyss were based on self-report measures, the lkelhood of expermenter bas s somewhat lessened. A further lmtaton of our study was that the therapes ncluded only dogs, wth the sole excepton of one combned dog/cat study. It s therefore mpossble to know how much of the observed mprovement resulted from anmal nteracton n general, versus nteracton wth a dog and/or nteracton wth the human facltatng treatment. It would also be valuable for research to assess the long-term effects of AAA/AAT. Ths would shed lght on whether the benefcal effects contnue after exposure to AAA/AAT and on the duraton of the effects. Lastly, research comparng ndvdual versus group nteractons s lackng, despte 177 Anthrozoös
Do Anmal-Asssted Actvtes Effectvely Treat Depresson? the fact that the effectveness of ndvdual versus group anmal vsts s an mportant practcal queston for therapsts who are plannng anmal nteracton programs. Techncally, our studes comprsed a heterogeneous array of treatments, but shared the mportant common thread of anmal nteracton. Only one study n the meta-analyss used AAT, precludng us from drectly comparng the effectveness of AAT versus the more general category AAA. For purposes of the meta-analyss, the benefts of ncludng another study on anmal nteracton and depresson outweghed the dsadvantage of havng two separate approaches represented n the same analyss. Further research s needed to contrast AAA versus AAT, but n the absence of such research, we beleve t s approprate to say that our results reflect the effectveness of AAA/AAT n general, especally gven that, as noted n the ntroducton, the two treatments are often not clearly dstngushed n actual practce. Thus we have extended our results to both types (AAA/AAT). Conclusons The results of our meta-analyss offer some emprcal support for the therapeutc effectveness of dog-asssted AAA/AAT for treatng depresson. Fve emprcal studes show that AAA/AAT has postve effects on depresson that are both statstcally sgnfcant and large enough to be of practcal sgnfcance. However, our survey of the lterature suggests that only a small proporton of the exstng research on AAA/AAT meets even mnmal standards of research desgn, and few focus on mportant physologcal measures such as blood pressure. Well-desgned studes specfcally focusng on physologcal measures such as blood pressure would be a useful addton to the exstng body of knowledge on AAA/AAT. Acknowledgements Ths artcle s based on a master s thess wrtten by M.S. We thank Steven Barger and Hed Wayment for ther helpful gudance on the desgn and analyses. Notes 1. Analyses usng a fxed effects model produced smlar fndngs and dd not affect conclusons. The authors would lke to thank an anonymous revewer for rasng the ssue. 178 Anthrozoös References References marked wth an astersk ndcate studes ncluded n the meta-analyss. Barba, B. E. 1995. The postve nfluence of anmals: Anmal-asssted therapy n acute care. Clncal Nurse Specalst 9(4): 199 202. Batson, K., McCabe, B., Baun, M. M. and Wlson, C. 1998. The effect of a therapy dog on socalzaton and physologcal ndcators of stress n persons dagnosed wth Alzhemer s dsease. In Companon Anmals n Human Health, 203 215, ed. C. C. Wlson and D. C. Turner. Thousand Oaks, CA: Sage Publcatons. Beck, A. T., Steer, R. A. and Brown, G. K. 1996. Manual for the Beck Depresson Inventory-II. San Antono, TX: Psychologcal Corporaton. Beck, A. T., Ward, C. H., Mendelson, M., Mock, J. and Erbaugh, J. 1961. An nventory for measurng depresson. Archves of General Psychatry 4: 53 63. Boldt, M. A. and Dellmann-Jenkns, M. 1992. The mpact of companon anmals n later lfe and consderatons for practce. The Journal of Appled Gerontology 11(2): 228 239. Brasc, J. R. 1998. Pets and health. Psychologcal Reports 83: 1011 1024. *Brckel, C. M. 1984. Depresson n the nursng home: A plot study usng pet-facltated psychotherapy. In The Pet Connecton: Its Influence on Our Health and Qualty of Lfe, 407 415, ed. R. K. Anderson, B. L. Hart, and L. A. Hart. Mnneapols, MN: Center to Study Human Anmal Relatonshps and Envronments, Unversty of Mnnesota. Brnk, T. L., Yesavage, J. A., Lum, O., Heersema, P. H., Adey, M. and Rose, T. L. 1982. Screenng tests for geratrc depresson. Clncal Gerontologst 1(1): 37 43.
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