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Relationship between diagnostic criteria, depressive equivalents and diagnosis of depression among older adults with intellectual disability L. Langlois 1 & L. Martin 2 1 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada 2 Master of Public Health, Lakehead University,Thunder Bay, ON, Canada Abstract Background Depression is more common among persons with an intellectual disability (ID) than the general population, and may be expected to increase with age just as in the general population. However, little is known about depression among older adults with ID. The literature has questioned the use of standard diagnostic criteria for depres- sion among both older adults and persons with ID, and behavioural depressive equivalents have been suggested. This study uses the interRAI ID assess- ment instrument to investigate the relationship between standard diagnostic criteria for depression, depressive equivalents and a diagnosis of depression among older and younger adults with ID in com- munity and institutional settings in Ontario, Canada. Method Items in the interRAI ID assessment instrument that were representative of The Diagnos- tic and Statistical Manual of Mental Disorders 4th Edition (DSM-IV) criteria and depressive equiva- lents were examined among persons with ID in institutional (census-level data) and in community- based (sample) residential settings. Bivariate logistic regression was used to examine the relationship between depressive symptoms and a diagnosis of depression. Descriptive statistics were used to examine the prevalence of depressive symptoms among those who did not have a diagnosis of depression. Results The results indicate that DSM-IV diagnos- tic criteria and depressive equivalents were signifi- cantly related to a diagnosis of depression among older and younger adults with ID, and that both types of symptoms were exhibited by a non-trivial proportion of individuals without a diagnosis of depression. Conclusions The depression rating scale embedded in the interRAI ID is helpful in identifying older adults at risk of depression. Contrary to other studies, few significant differences were found in depressive symptoms by age. Keywords depression, depressive equivalents, diagnostic criteria, intellectual disability, older adults Introduction Major depression has been identified as the leading cause of disability in developed nations (Murray & Correspondence: Lynn Martin, Lakehead University, 955 Oliver Road, Thunder Bay ON, P7B 5E1, Canada (e-mail: lynn.martin@ lakeheadu.ca). Journal of Intellectual Disability Research doi: 10.1111/j.1365-2788.2008.01041.x volume 52 part 11 pp 896904 november 2008 896 © 2008 The Authors. Journal Compilation © 2008 Blackwell Publishing Ltd

Relationship between diagnostic criteria, depressive equivalents and diagnosis of depression among older adults with intellectual disability

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Page 1: Relationship between diagnostic criteria, depressive equivalents and diagnosis of depression among older adults with intellectual disability

Relationship between diagnostic criteria, depressiveequivalents and diagnosis of depression among olderadults with intellectual disability

L. Langlois1 & L. Martin2

1 Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada2 Master of Public Health, Lakehead University,Thunder Bay, ON, Canada

Abstract

Background Depression is more common amongpersons with an intellectual disability (ID) than thegeneral population, and may be expected toincrease with age just as in the general population.However, little is known about depression amongolder adults with ID. The literature has questionedthe use of standard diagnostic criteria for depres-sion among both older adults and persons with ID,and behavioural depressive equivalents have beensuggested. This study uses the interRAI ID assess-ment instrument to investigate the relationshipbetween standard diagnostic criteria for depression,depressive equivalents and a diagnosis of depressionamong older and younger adults with ID in com-munity and institutional settings in Ontario,Canada.Method Items in the interRAI ID assessmentinstrument that were representative of The Diagnos-tic and Statistical Manual of Mental Disorders 4thEdition (DSM-IV) criteria and depressive equiva-lents were examined among persons with ID ininstitutional (census-level data) and in community-

based (sample) residential settings. Bivariate logisticregression was used to examine the relationshipbetween depressive symptoms and a diagnosis ofdepression. Descriptive statistics were used toexamine the prevalence of depressive symptomsamong those who did not have a diagnosis ofdepression.Results The results indicate that DSM-IV diagnos-tic criteria and depressive equivalents were signifi-cantly related to a diagnosis of depression amongolder and younger adults with ID, and that bothtypes of symptoms were exhibited by a non-trivialproportion of individuals without a diagnosis ofdepression.Conclusions The depression rating scale embeddedin the interRAI ID is helpful in identifying olderadults at risk of depression. Contrary to otherstudies, few significant differences were found indepressive symptoms by age.

Keywords depression, depressive equivalents,diagnostic criteria, intellectual disability, olderadults

Introduction

Major depression has been identified as the leadingcause of disability in developed nations (Murray &

Correspondence: Lynn Martin, Lakehead University, 955 OliverRoad, Thunder Bay ON, P7B 5E1, Canada (e-mail: [email protected]).

Journal of Intellectual Disability Research doi: 10.1111/j.1365-2788.2008.01041.x

volume 52 part 11 pp 896–904 november 2008896

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Lopez 1997). In the general population, the preva-lence of depression in a given year is approximately4.1%–4.6% for adults (Health Canada 2002).Depression is even more common among olderadults (i.e. those aged 65+ years), and is experi-enced by between 8% and 20% of those residing inthe community (Gallo & Lebowitz 1999; Alexopou-los et al. 2002) and between 17% and 37% of thosein primary care (Gurland et al. 1996). Psychiatricillness is known to be even more common amongpersons with intellectual disability (ID), and isexperienced by 14% to 67% of the population(Brown & Percy 1999). In particular, depressionaffects approximately 4.6% of adults with ID at anyone point in time (Cooper et al. 2007), and hasbeen associated with up to a fourfold increase com-pared with the general population, over time(Richards et al. 2001). It is also expected that, as inthe general population, the risk of depression willincrease with age among persons with ID (Thorpe1998).

Although depression rates are high amongpersons with ID, they are estimated to be evenhigher – diagnostic difficulties associated with thispopulation may contribute to under-detection. Forexample, individual-level (e.g. impaired communi-cation skills) (Marston et al. 1997; Prosser &Bromley 1998; Clarke & Gomez 1999; Ross &Oliver 2002), physician-level (e.g. the tendency ofprofessionals to attribute behavioural and psychiat-ric symptoms to the person’s ID rather than anunderlying psychiatric syndrome or, diagnostic over-shadowing) (Balboni et al. 2000; Deb et al. 2001),and system-level (e.g. lack of regular contact with aphysician) characteristics and barriers contribute tothe under-detection of depression among personswith ID. Thus, it is important to use standardiseddiagnostic criteria and reliable and valid assessmentmethods to detect and diagnose depression.

The Diagnostic and Statistical Manual of MentalDisorders 4th Edition (DSM-IV) provides a standardset of criteria upon which a formal diagnosis ofmajor depression is based (APA 1994), and theseare generally applicable to adults with mild to mod-erate forms of ID (Tsiouris 2001). However, itsappropriateness has been questioned in relation topersons with severe or profound ID. In fact, severalresearchers attest to the differential presentation ofdepression in this subset of the ID population, and

suggest the use of ‘depressive equivalents’ (e.g.aggression, self-injury, screaming) in addition tostandard diagnostic criteria (Sovner & Hurley 1983;Ross & Oliver 2002), and the Royal College of Psy-chiatrists in the UK have published a list of diag-nostic criteria for use with adults with ID diagnosticcriteria for psychiatric disorders for use with adultswith ID (Diagnostic Criteria for psychiatric disor-ders for use with adults with learning disabilities/mental retardation) that includes several depressiveequivalents (Smiley & Cooper 2003). However,Holden & Gitlesen (2004) have argued against theuse of these equivalents because of the resultingincreased rate of persons falsely identified as havingdepression (i.e. false positives).

Like older adults in the general population, agingadults with ID may be at increased risk of depres-sion (Cooper 1997; Davidson & Janicki 2001).Given this, there is a need to better understand thesymptoms of depression among older adults withID. The objectives of this paper are twofold. First,to determine what characteristics are associatedwith a diagnosis of depression among older adultswith ID by examining the relationship betweenDSM-IV diagnostic criteria, depressive equivalentsand diagnosis of depression. Second, to determinethe extent to which depression goes undetectedamong older adults with ID by examining the ratesof depressive symptoms among those without adiagnosis of depression.

Method

Samples

Two samples were used to carry out the analyticactivities for this study.The first consisted of asample of 480 community-dwelling adults with IDassessed during two separate studies (see below).These agencies are funded by the Ontario Ministryof Community and Social Services, and provide resi-dential and other supports (e.g. instrumental andactivities of daily living) to persons with ID to helpmaximise their independence in the community.1) 274 adults in four community-based agenciesthat provide residential services were assessed aspart of the original pilot study of the interRAI IDassessment instrument (Martin et al. 2007), where25.2% (n = 69) were 50 years of age or more; and2) 206 older adults (i.e. aged 50 years or more)

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with ID in five community-based agencies thatprovide residential services to persons with ID wereassessed in 2006 as part of a study funded by theCanadian Institutes of Health Research granted tothe co-author.

The second dataset consisted of census-levelinformation on all residents in Ontario’s threeremaining institutional settings for persons with ID.In 2005, the Ontario Ministry of Community andSocial Services contracted the ideas for Health teamat the University of Waterloo to get a population-level view of the needs of residents as they plan forthe transition to the community. The data used herewere based on residents’ most recent assessment(i.e. summer 2006). Of the 822 residents, 57.8%(n = 475) were 50 years of age or older.

Measure

Instrumentation

InterRAI is a not-for-profit international researchorganization that has developed comprehensiveassessment systems for use in various social andhealth settings, including home care, long-termcare, mental health and the developmental sector(http://www.interrai.org). Instruments were designedto provide information on the persons’ currentstatus across all key life domains, and use acommon language to facilitate communicationbetween professionals and across sectors.

The interRAI ID is a standardised, comprehen-sive assessment instrument that evaluates thestrengths, preferences and needs of adults with ID,regardless of level of cognitive impairment and resi-dential setting. The interRAI ID was designed to becompatible with interRAI instruments mandated bythe Ontario Ministry of Health and Long-TermCare in all home care (RAI-Home Care), long-termcare (RAI 2.0) and inpatient psychiatric (RAI-Mental Health) service settings. Martin et al. (2007)have provided evidence of the psychometric proper-ties of the interRAI ID instrument; and findingsrelated to embedded measures of functioning,physical health and psychopathology are brieflydescribed below.

Depressive criteria. Items in the interRAI ID relatedto both DSM-IV-related depressive criteria anddepressive equivalents will be used. Table 1 shows

the interRAI ID items used to represent bothDSM-IV-related criteria and depressiveequivalents.

As part of the interRAI ID assessment, assessorsrecord the presence of a known diagnosis of activedepression (e.g. documented in the person’s record,communication from a physician or other clinician).Previous research has shown that assessors recordthe presence of a depression diagnosis among theelderly with good reliability (kappa = 0.65) (Landis& Koch 1977), a level of precision that comparesfavourably with reliability estimates of other toolsused in psychiatric epidemiology (Eaton et al.2000).

Embedded measures in the interRAI ID. A number ofmeasures may be derived using items in the inter-RAI ID, including measures of depression, aggres-sion and cognitive performance. The depressionrating scale (DRS) is a summary scale with scoresranging from 0 to 14, and is based on the presenceof seven indicators of depressed mood; a score of 3

or more is considered to be reflective of possibleclinical depression (Burrows et al. 2000). Theaggressive behaviour scale is a summary scale basedon the presence of verbal or physical abuse, sociallyinappropriate or disruptive behaviour and resistingcare. Its scores vary between 0 and 12, where higherscores reflect higher levels of aggression. Both scaleshave demonstrated psychometric properties inpersons with ID (Martin et al. 2007, 2007a,b). Thecognitive performance scale (CPS) is a predictivealgorithm describing cognitive status based onshort-term memory, decision-making, expressionand self-performance in eating (Morris et al. 1994).Scores range from Intact (0) to Very severelyimpaired (6). The CPS will be used as a proxy forlevel of severity of ID (i.e. borderline, mild, moder-ate, severe, profound), as approximately one quarter(24.4%) of persons in this study did not have adocumented level of ID in their records. The use ofthis scale has been shown to be both reliable andvalid among persons with ID, and highly correlatedto level of ID severity (Martin et al. 2007).Here, CPS scores between 0 and 4 refer tomild to moderate cognitive impairment, whilescores of 5 or 6 refer to more severe cognitiveimpairment.

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Results

Demographic characteristics

Table 2 presents select demographic characteristicsfor the study sample. Overall, persons were male, intheir early fifties and had severe cognitive impair-ment. Gender, residence and level of cognitiveimpairment did not differ significantly by age.Overall, 15.6% had a diagnosis of depression docu-mented on their interRAI ID assessment, and thisrate did not differ significantly by age or residential

status (i.e. between older adults living in commu-nity vs. institutional settings).

Relationship between diagnostic criteria,depressive equivalents and diagnosis

Table 3 shows the result of bivariate logistic regres-sion analyses modelling the relationship between adiagnosis of depression and each interRAI ID itemrelated to either DSM-IV criteria or depressiveequivalents.

Table 1 InterRAI ID items matched toDSM-IV criteria and behaviouraldeterminants

DSM-IV criteria InterRAI ID items

Depressed mood Sad, pained, worried facial expressionsReports feeling sad, depressed, hopelessCrying, tearfulnessMade negative statementsPersistent anger with self or othersOutburst of anger

Anhedonia Expressions (also non-verbal) of lack of pleasureReports little interest in things normally enjoyed

Feelings of worthlessness Expressions of guilt or shameRecurrent thoughts of death,

suicidal ideation–

Decrease in appetite Increase or decrease in normal appetiteSignificant weight loss or gain Weight loss of 5%+ in 30 days or 10%+ in 180 days

Weight gain of 5%+ in 30 days or 10%+ in 180 daysInsomnia or hypersomnia Sleep problemsPsychomotor agitation or

retardation–

Fatigue or loss of energy FatigueDiminished ability to think or

concentrateEasily distractedMental function varies over the course of the day

Diagnosis of depression Provisional diagnostic category: mood disorderPossible clinical depression Depression rating scale score of 3 or more

Depressive equivalents

Aggression Verbal abusePhysical abuseResists careDestructive behaviourAggressive behaviour scale

Self-injury Self-injurious behaviourScreaming Socially inappropriate/disruptive behaviourStereotypies Unusual physical movements/stereotypies

InterRAI ID, interRAI intellectual disability; DSM-IV, Diagnostic and Statistical Manual ofMental Disorders 4th Edition.

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The results show that persons with a diagnosis ofdepression were significantly more likely to alsoexhibit depressive symptoms related to DSM-IVdiagnostic criteria for depression. Overall, amongthose with diagnosed depression, having a DRSscore exceeding the threshold (i.e. 3 or more) wasalmost three times more likely than having a scorelower than the threshold. With the exception of lackof pleasure (or anhedonia), older adults with a diag-nosed mood disorder were in fact more likely toexhibit most of the DSM-IV criteria related to sadmood where facial expressions, self-reported sadmood, negative statements, outbursts of anger andexpressions of guilt or shame were especially impor-tant. A diagnosis of depression was also associatedwith increased likelihood of exhibiting somaticsymptoms such as change in appetite, fatigue, beingeasily distracted and having mental function thatvaries over the course of the day, although weightloss, weight gain and sleeping problems were not.These relationships did not differ significantly byage, with the exception of change in appetite andfatigue, which were significant only amongdepressed older adults.

Similarly, persons with a diagnosis of depressionwere more likely to exhibit almost all of the listeddepressive equivalents; only the presence of stereo-typies was unrelated to diagnosis. Overall, personswith a diagnosis of depression were almost threetimes more likely to show mild to moderate levels

of aggression, and over seven times more likely toshow severe aggression (odds ratio = 2.72). Again,the direction of these relationships did not differ byage, although some indicators were more importantamong older adults (i.e. verbal abuse), and otherswere more important among younger adults (i.e.physical abuse and resisting care).

Symptoms of depression among those withouta diagnosis

Table 4 shows the prevalence of DSM-IV-relatedcriteria and depressive equivalents among personswho do not have a diagnosis of depression. Theresults show that a non-trivial proportion of personsin the study exhibited both DSM-IV criteria relatedto sad mood and somatic symptoms. With theexception of older adults having higher rates offatigue (P < 0.0001), the rates for other diagnosticcriteria did not differ by age. Depressive equivalentswere also common, where aggression and self-injurious behaviour were the most prevalent. Olderadults without a diagnosis of depression tended toexhibit self-injurious behaviour less frequently thanyounger adults (P = 0.01), although rates for allother indicators were unaffected by age.

Discussion

Overall, a significant proportion of persons with IDin this study had a documented diagnosis of depres-

Table 2 Demographic characteristics

All

Age group

18–49 years 50+ yearsP-value(n = 1302) (n = 560) (n = 742)

Mean age (SD) 51.4 (11.7) 41.4 (7.7) 58.9 (7.8) <0.001Male 58.6% 60.1% 57.4% 0.34Residence

Community 36.9% 38.0% 36.0% 0.45Institution 63.1% 62.0% 64.0%

Level of cognitive impairmentMild to moderate

(CPS 0–4)42.2% 39.6% 44.1% 0.11

Severe (CPS 5+) 57.8% 60.4% 55.9%Documented diagnosis of

depression15.6% 13.9% 16.9% 0.15

CPS, the cognitive performance scale.

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sion and showed both DSM-IV-related symptomsof depression and depressive equivalents. The mostcommonly exhibited DSM-IV-related criteriaincluded sad facial expressions, crying/tearfulness,distraction, fatigue and varying mental function,whereas socially inappropriate behaviour and self-injurious behaviour were the most frequently seendepressive equivalents. Each of these symptoms wasalso highly related to the presence of a depressiondiagnosis. Further, the DRS embedded in the inter-RAI ID assessment instrument was highly related toa diagnosis of depression.

The notion of ‘depression without sadness’ hasbeen used to describe the tendency of older adultsin the general population to exhibit anhedonic andsomatic symptoms rather than those related to sad

mood (Gallo et al. 1997). The differential presenta-tion of symptomology is thought to contribute tohigher rates of under-detection of depression amongolder adults. For this reason, it was not surprisingthat the most important indicators of depression,i.e. those related to sad mood, were highly relatedto a diagnosis of depression among older adults,nor that somatic symptoms played an importantrole among older adults. This study also found thatsomatic symptoms and symptoms related to sadmood were present among a non-trivial proportionof persons without a diagnosis of depression. Thesesymptoms were exhibited with similar frequencyamong older and younger adults.

As it has been suggested that behavioural indica-tors of possible depression (i.e. depressive equiva-

Table 3 Bivariate relationships with diagnosis of depression

All

Age group

18–49 years 50+ years(n = 203) (n = 78) (n = 125)OR (95% CI) OR (95% CI) OR (95% CI)

DSM-IV-related criteriaSad, pained, worried facial expressions 1.9 (1.4–2.6) NS 2.2 (1.5–3.3)Reports feeling sad/depressed/hopeless 2.5 (1.3–4.9) NS 3.4 (1.6–7.5)Crying, tearfulness 2.3 (1.5–3.5) 2.7 (1.4–5.1) 2.0 (1.1–3.6)Made negative statements 2.7 (1.6–4.6) NS 2.9 (1.5–5.4)Persistent anger with self or others 2.9 (1.9–4.3) 2.6 (1.2–5.3) 3.0 (1.7–5.0)Outburst of anger 2.9 (1.9–4.3) NS 4.1 (2.4–6.9)Expressions of lack of pleasure NS NS NSReports little interest in things normally enjoyed 4.5 (2.3–9.1) 4.1 (1.3–12.8) 4.8 (2.0–11.5)Expressions of guilt or shame 2.8 (1.4–5.7) NS 2.9 (1.3–6.4)Depression Rating Scale (DRS) score 3+ 2.8 (1.9–3.9) 2.2 (1.2–4.0) 3.1 (2.0–4.8)Increase or decrease in normal appetite 2.5 (1.2–5.4) NS 3.2 (1.3–7.8)Weight loss NS NS NSWeight gain NS NS NSSleep problems NS NS NSFatigue 1.7 (1.2–2.3) NS 1.9 (1.3–2.8)Easily distracted 2.3 (1.6–3.2) 3.2 (1.7–5.8) 1.9 (1.3–2.9)Mental function varies over the course of the day 2.5 (1.8–3.3) 3.0 (1.8–4.9) 2.2 (1.5–3.2)

Depressive equivalentsVerbal abuse 3.5 (2.3–5.6) NS 5.6 (3.2–9.9)Physical abuse 2.2 (1.2–3.8) 2.9 (1.3–6.4) NSResists care 2.2 (1.3–3.7) 2.7 (1.2–5.8) NSDestructive behaviour 2.1 (1.1–3.8) NS NSAggressive Behaviour Scale (ABS) 2.7 (2.1–3.6) 2.7 (1.8–4.1) 2.8 (2.0–4.0)Self-injurious behaviour 2.0 (1.3–3.0) 1.9 (1.0–3.6) 2.1 (1.2–3.8)Socially inappropriate/disruptive behaviour 1.8 (1.3–2.6) 2.1 (1.2–3.5) 1.7 (1.1–2.7)Unusual physical movements/stereotypies NS NS NS

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lents) are needed in addition to standard DSM-IVcriteria to detect depression among persons withsevere ID, it was not surprising that depressiveequivalents were significantly related to the presenceof a depression diagnosis, especially given that themajority of older adults in the sample experiencedhigher levels of cognitive impairment. Although thisdiagnosis was associated with an increased risk ofaggression, self-injury and socially inappropriate ordisruptive behaviour among older and youngeradults, it was related to verbal abuse only amongolder adults, and to physical abuse and resistingcare only among younger adults. Depressive equiva-lents were quite common among those without a

diagnosis of depression. Here, older adults tendedto exhibit self-injurious behaviour less frequentlythan younger adults, although prevalence rates forall other indicators were unaffected by age. Thisfinding was somewhat unexpected, as the literaturereports higher rates of differential symptoms ofdepression with increasing age.

This study does pose some limitations. First,items of analyses were limited to those items thatare available in the interRAI ID assessment. Forthis reason, it was not possible to investigate therelationship between all DSM-IV-related criteriaand depression. For example, psychomotor agitationor retardation and suicidal ideation could not be

Table 4 Symptoms of depression amongpersons without a diagnosis of depression

All

Age group

18–49 years 50+ years(n = 1099) (n = 482) (n = 617)

DSM-IV related criteriaSad, pained, worried facial expressions 33.9% 32.6% 34.9%Reports feeling sad/depressed/hopeless 2.8% 2.9% 2.8%Crying, tearfulness 8.2% 8.7% 7.8%Made negative statements 4.1% 3.1% 4.9%Persistent anger with self or others 7.5% 7.1% 7.8%Outburst of anger 7.5% 8.5% 6.7%Expressions of lack of pleasure 2.5% 1.7% 3.1%Reports little interest in things normally

enjoyed1.7% 1.7% 1.8%

Expressions of guilt or shame 2.2% 1.2% 2.9%Depression Rating Scale (DRS) score 3+ 13.2% 12.0% 14.1%Increase or decrease in normal appetite 2.0% 1.9% 2.1%Weight loss 3.2% 3.1% 3.2%Weight gain 3.0% 3.7% 2.4%Sleep problems 7.9% 8.1% 7.8%Fatigue 25.3% 17.6% 31.3%Easily distracted 56.2% 58.9% 54.1%Mental function varies over the course

of the day29.5% 28.0% 30.6%

Depressive equivalentsVerbal abuse 5.4% 6.0% 4.9%Physical abuse 4.3% 4.8% 3.9%Resists care 5.3% 5.2% 5.4%Destructive behaviour 3.7% 4.6% 3.1%Aggressive Behaviour Scale (ABS): None 46.6% 45.5% 47.5%Aggressive Behaviour Scale (ABS): Mild-Mod. 49.1% 49.5% 48.8%Aggressive Behaviour Scale (ABS): Severe 4.3% 5.0% 3.7%Self-injurious behaviour 9.3% 11.8% 7.3%Socially inappropriate/disruptive behaviour 17.3% 18.5% 16.4%Unusual physical movements/stereotypies 6.4% 5.0% 7.5%

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examined. Second, the small number of personswith a diagnosis of depression limited the ability toconduct multivariate regression analyses. Specifi-cally, it is thought that DSM-IV criteria are usefulfor diagnosing depression among those with mild/moderate levels of cognitive impairment, but maynot be as useful for individuals with severe cognitiveimpairment. With a larger sample size, it would beuseful to consider the impact of the person’s levelof cognitive impairment in the relationship betweendepressive equivalents and a diagnosis of depres-sion, as well as develop a multivariate model thatincluded both standard diagnostic criteria anddepressive equivalents. Third, it may be that thelimitations of standard diagnostic criteria fordepression among persons with ID led to under-detection of the problem among some individuals.Consequently, the rates of depressive symptoms anddepressive equivalents in the ‘non-depressed’ groupmay be inflated. Fourth, as the dataset representedprimarily institutionalised adults, this could limitthe generalisability to other populations (e.g.persons supported in community housing, personsliving independently in the community and personsliving in the community with family). Finally, whileit is generally acknowledged that this populationexperiences premature aging (Nehring 2005), thereis some disagreement as to the most appropriateage cut-point to delineate ‘old age’. The age of 50

years or more was chosen in this study, although itmay have been too conservative and contributed tothe lack of significant findings. That said, rates andrelationships were retested using a cut-off of 55

years or more, and these yielded similar results(available upon request). Cut-offs of 60 or 65 yearsmay have shown differences, although such analyseswere not possible given the sample size. Over time,these analyses could be replicated in larger datasets,using alternative cut-points for age.

Conclusion

The results of this study have shown that DSM-IVdiagnostic criteria and depressive equivalents weresignificantly related to a diagnosis of depressionamong older and younger adults with ID. Theresults also showed that both types of symptomswere exhibited by a non-trivial proportion of older

and younger adults with ID. Most importantly, asubstantial proportion of older adults with ID whoshow clinically relevant signs of depression do nothave a diagnosis of depression. In particular, 70.7%who exceeded the threshold score on the DRSscore did not have a recognised depression,although results showed that exceeding this thresh-old was highly associated with risk of depressiondiagnosis. Assessment systems that are compatiblewith the interRAI ID have been mandated for usein several service settings in Ontario, includingadult inpatient psychiatry, home care and long-termcare. Clinicians in these settings should pay specialattention to the DRS scores of older adults with IDwhen developing the plan of care.

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Accepted 21 December 2007

904Journal of Intellectual Disability Research volume 52 part 11 november 2008

L. Langlois & L. Martin • Diagnostic criteria, depressive equivalents and diagnosis of depression

© 2008 The Authors. Journal Compilation © 2008 Blackwell Publishing Ltd