University of Glasgow, Scotland, UK
Correspondence: Professor Colin A. Espie, Department of Psychological Medicine, Gartnavel Royal Hospital, 1055 Great Western Road, Glasgow G12 0XH, UK. E-mail: c.espie{at}clinmed.gla.ac.uk
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ABSTRACT |
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Aims To develop a scale for individuals with learning disability, and a supplementary scale for carers.
Method Items were generated from a range of assessment scales and through focus groups. A draft scale was piloted and field tested using matched groups of people with or without depression, and their carers. The scale was also administered to a group without learning disabilities for criterion validation.
Results The Glasgow Depression Scale for people with a Learning
Disability (GDSLD) differentiated depression and non-depression groups,
correlated with the Beck Depression Inventory II (r=0.88),
had good testretest reliability (r=0.97) and internal
consistency (Cronbach's =0.90), and a cut-off score (13) yielded 96%
sensitivity and 90% specificity. The Carer Supplement was also reliable
(r=0.98;
=0.88), correlating with the GDSLD
(r=0.93).
Conclusions Both scales appear useful for screening, monitoring progress and contributing to outcome appraisal.
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INTRODUCTION |
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METHOD |
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Development of the item pool
We reviewed the content of existing diagnostic schedules and symptom scales
to identify a descriptive pool of items. Our intention was to represent the
breadth of depressive symptoms commonly reported, while keeping in mind our
goal of developing a brief measure. We took, as our starting point, the
depression sub-scale from the recently developed DCLD
(Royal College of Psychiatrists,
2001). The DCLD has been specifically developed for use in
learning disability and contains items not included in diagnostic schedules
developed for the general population. Seventeen items were taken from this
schedule and an additional four, non-overlapping, items were taken from ICD-10
(World Health Organization,
1994) and DSM-IV (American
Psychiatric Association, 1994). Several published depression
scales were also reviewed: the Beck Depression Inventory - II (BDI-II;
Beck et al, 1996), the
Hamilton Rating Scale for Depression
(Hamilton, 1960) and the Zung
Self-Rating Depression Scale (Zung,
1965). From these, seven further items were added to the pool,
making 28 items in total.
Focus groups
Twelve people with mild-to-moderate learning disability (mild,
n=8; moderate, n=4) participated in the focus groups. There
were six men and six women, aged 26-60 years (mean 42.25 years, s.d. 10.31).
Mean age equivalent for receptive verbal comprehension on the British Picture
Vocabulary Scale (BPVS; Dunn et
al, 1997) was 8.95 years (s.d. 1.90). Participants were
divided into two groups of six.
Our aim was to observe the type of language and expression commonly used to describe affect. Participants were given pictorial presentations of emotional events and facial expressions and were asked to discuss what was happening and how the people involved might be feeling. Facial expressions were taken from the Boardmaker computer program (Mayer-Johnson Inc., Solana Beach, CA, 1997) and pictorial images from the Life Horizons 35-mm slide set (Kempton, 1988). We followed published procedures for running focus groups and analysing resultant data (Morgan, 1993). A facilitator assisted the group to focus on tasks and interact when the situations were discussed. Both groups were audiotape-recorded and the proceedings transcribed. Transcribed material was reviewed and each word used to describe an emotion was logged and its frequency counted. The most frequently occurring words relating to depressive symptoms were subsequently used to compose adapted questions reflecting the content of the pool items. Examples for the emotion sad included sad, crying, upset, low, down and miserable; words for happy included happy, pleased, smiling and in a good mood. Such information helped us to generate appropriate phrasings for items.
Development of the response format
In constructing the draft scale, several response options were considered.
Lindsay & Michie (1988)
found a two-choice format (i.e. presence or absence of symptoms) to have
higher testretest reliability than a four-choice format in this
population. However, we felt that dichotomies were unlikely to be sensitive to
changes in specific symptoms over time, and might lead some people with
learning disability to respond perseveratively, or in an acquiescent manner
(Flynn, 1986). A three-point
format was therefore selected, in which the responses were
never/no (0), sometimes (1), and a
lot/always (2) (note that some items were reverse rated). However, we
decided to retain the option of presenting items in two stages: the first
requiring a yes/no answer indicating the presence or absence of
the symptom in question, and the second requiring an indication of the
severity of the symptom if present (sometimes or a
lot/always). To combat possible acquiescence and to overcome expressive
language problems, symbols were also available to represent each answer
(Kazdin et al, 1983).
Participants were encouraged to point to the symbol that best described how
they felt. All symbols were presented on 15 cm x 10 cm card with the
word in large print (36 point) and the symbol (from Boardmaker) occupying a
sizeable proportion of available space; yes was a large white
tick on a black background; no a large black cross on a white
background; sometimes a small black puddle mark on
a white background; and always a large black
puddle mark on a white background. A screening process was also
developed to assess understanding of the response terms. This included a
series of factual questions, unrelated to the scale, to test the respondent's
ability to discriminate reliably between yes and
no (e.g. Do you live in Scotland?) and between
sometimes and always (e.g. Do you have fish
for tea?) and to understand the symbols (e.g. Which card means
"always"?) (Further details available from the authors upon
request.) Finally, it was decided to ensure that the scale reflected
present state symptoms by presenting each question in terms of
how the person had felt in the previous week. This was achieved by
establishing an anchoring event which had occurred 1 week
before.
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RESULTS |
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Field testing and psychometric development
Three experimental groups were included in this part of the study: people
with learning disabilities and depression, identified consecutively from
learning disability psychiatry clinics; people with learning disabilities but
no depression, identified as age- and gender-matched controls through local
day centres; and people without learning disabilities but with depression,
identified through clinical psychology outpatient clinics. The
learning-disability non-depression group was required to ascertain
discriminant validity of the GDSLD, and the non-learning-disability
depression group was required to permit criterion measurement against which to
validate the GDSLD. Two carers for people with learning disabilities
were also required to evaluate interrater reliability of the Carer Supplement
to the GDSLD (GDSCS).
Participants
Clinicians and day centre staff were provided with guidelines detailing the
following inclusion and exclusion criteria. For the learning-disability
depression group, participants had to have mild-to-moderate learning
disability with reasonable verbal comprehension, an ability to communicate
verbally and a current clinical diagnosis of depression. Criteria for the
learning-disability non-depression group were similar, although individuals
were required not to have a current diagnosis of depression. Individuals were
also excluded if they had a diagnosis of autism or dementia. Criteria for
inclusion in the non-learning-disability depression group comprised current
attendance at adult mental health services and a current clinical diagnosis of
depression according to DSM-IV criteria.
Once participants had been identified and had consented to take part, their carers were interviewed, during which the Mini-Psychiatric Assessment Schedule for Adults with a Developmental Disability (Mini-PASADD; Prosser et al, 1996) was completed. This is a standard assessment for evaluation of psychiatric disorder in people with a learning disability, and was used to confirm that individuals with learning disability had been allocated to the correct groups. All participants were so confirmed. Of the 40 people with learning disability who were approached to take part, two of their carers refused involvement and gave no reason for this. This left 19 people in the learning-disability depression group (10 male, 9 female; mean age 40.21 years, (s.d.=12.20) and another 19 in the learning-disability non-depression group (10 male, 9 female; mean age 39.11, s.d.=9.31). British Picture Vocabulary Scale age equivalents were similar across these groups: 15 people with mild and 4 with moderate learning disability, BPVS mean 9.28 years (s.d.=1.80) in the depression group v. 10 people with mild and 9 with moderate learning disability, BPVS mean 9.18 years (s.d.=2.06) in the non-depression group. There was no significant difference between the depression and non-depression learning-disability groups in terms of age, gender, degree of disability or BPVS results. For the non-learning-disability depression group, 27 patients were recruited (12 male, 15 female; mean age 43.89 years, s.d.=13.41). These participants did not differ significantly from the participants with learning disabilities in age or gender distribution.
Validity
Content validity The method so far supports the content validity
of the GDSLD. Furthermore, none of the 20 retained items was assigned a
score of 0 (or 2 if reverse rated) by more than half of the
learning-disability depression group, suggesting that the content was
appropriate to their experience.
Discriminant validity Preliminary checks of skewness and kurtosis verified that our data were suitable for parametric analysis. The ability of the GDSLD to discriminate between the three experimental groups is illustrated in Fig. 1. Inspection of these data suggests that the scale discriminates effectively between the depression and non-depression groups in terms of levels of depression reported. This was confirmed by one-way analysis of variance (F=44.45; d.f.=2; P < 0.001) and a Scheffé post hoc test (P < 0.05) demonstrated that there was a significant difference between the depression (mean 23.37, s.d.=6.3) and non-depression (mean 9.26, s.d.=2.94) learning-disability groups. Participants in the non-learning-disability depression group obtained scores similar to counterparts with learning disability and depression (mean 22.48, s.d.=5.77) and significantly higher than those with learning disability who were without depression (Scheffé test, P < 0.05).
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Criterion validity To investigate criterion validity, the 27 participants in the non-learning-disability depression group completed both the GDSLD and the BDIII. A scatterplot of the relationship between scores on these measures (Fig. 2) demonstrates a strong linear relationship with no outlier cases. Data were analysed using the product moment correlation, which yielded r=0.94, P < 0.001, signifying excellent criterion validity. Retaining only those items that have no overlap with the BDIII (items 5, 16-20) this correlation remained strong (r=0.84; P < 0.001).
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Reliability
Testretest reliability We measured testretest
reliability by administering the GDSLD at the beginning and the end of
assessment sessions with all the participants with learning disabilities
(n=38). In between these presentations of the GDSLD the BPVS
was administered and the participant was engaged in general conversation.
Testretest reliability was found to be high (r=0.97;
P < 0.001) and it remained strong when recalculated using only the
scores from participants with depression and learning disabilities
(r=0.94; P < 0.001, n=19).
Internal consistency Internal consistency was assessed by
calculation of Cronbach's , which revealed highly satisfactory values.
A value of
=0.70 or above is considered to be acceptable
(Nunnally, 1978). Alpha was
0.90 for the total scale (n=38), with the range in internal
consistency, as measured by
if item deleted, being 0.89 to 0.91 (mean
0.90). When n=19 (the learning-disability depression group only),
remained satisfactory at 0.81, with a range of 0.77 to 0.82 and a mean
if item deleted of 0.80. Mean itemtotal correlation was
calculated at 0.38.
Sensitivity and specificity
Sensitivity and specificity values for several cut-off points on the
GDSLD were also calculated. Sensitivity refers to the ability of the
scale to identify correctly all those who belong to a particular group (in
this case people with depression) and specificity refers to the likelihood of
people outwith the group (those without depression) being wrongly included. We
suggest that a score of 15 on the GDSLD is optimal if the intention is
to exclude those who are not depressed (specificity 100%). This score also
yielded acceptable sensitivity (90%). However, it might be clinically more
important to identify more people with possible depression than to avoid
false-positive results. Using a score of 13 as the cut-off point increased the
sensitivity to detect individuals with depression to 96%, decreasing
specificity to a still-acceptable 90%. We found that a cut-off of 10 would
detect 100% of those with depression, but at this point specificity dropped
considerably, to 68%. In light of the importance of detecting those with
depression, without wrongly identifying those not depressed, 13 might be
advisable as the cut-off point for screening purposes.
The Carer Supplement
The principal contribution that carers can make to the assessment of
depression is to report their direct observations and concerns. The
development of the GDSCS was an attempt to do this in a systematic way.
It was developed by first asking three clinical psychologists working in
learning disabilities to indicate independently which items of the
GDSLD they felt were overtly observable. The 16 items unanimously
selected were then included in a draft scale (see Appendix 2). Second, the
GDSCS was piloted using six carers (four family members, two paid
carers) of people with learning disability (three with depression, three
without depression). The carers were asked to give their opinion regarding
ease of understanding and completion. No item needed to be altered at this
stage. Third, the GDSCS was administered independently to two carers
for each of the participants in our learning-disability groups (76 carers). To
avoid situational influences, in each case carers were either both paid
carers, or both family members. Items were screened for relevance, but no item
was scored 0 by more than half of the carers of participants with depression.
No item had to be removed under this criterion, highlighting the content
validity of the GDSCS. Fourth, testretest reliability after a
delay of approximately 2 days was computed using the principal carer of each
participant, and was found to be high (r=0.98; P < 0.001,
n=38) for the total group, and similarly high for the depression
group alone (r=0.94; P < 0.001, n=19).
Inter-test reliability between the GDSLD and the GDSCS was also
high (r=0.93; P < 0.001, n=38): for the
learning-disability depression group r=0.87 (P < 0.001,
n=19). Interrater reliability between all pairs of carers (38 pairs)
was calculated at r=0.98 (P < 0.001), and for carers of
people with depression (19 pairs) r=0.93 (P < 0.001).
Internal consistency assessed using Cronbach's was 0.88 for the total
scale (n=38); the range in internal consistency, measured by
if item deleted, was 0.86 to 0.90 (mean 0.88).
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DISCUSSION |
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Our findings also demonstrate that the GDSLD and the GDSCS are internally consistent and have good testretest reliability. Inter-test reliability between the patient and carer versions was also high, suggesting that the GDSCS might be used to assess non-verbal or non-compliant individuals. Interrater reliability between carers was also high, although this result is based solely upon care provision within the same setting. It would be interesting, therefore, to administer the GDSCS independently to family carers and to staff carers and to compare the scores obtained, and to consider inter-administrator reliability on the GDSLD (F.M.C. administered this test to all participants with learning disabilities in our study).
The GDSLD took 10-15 min to administer, depending on the ability and cooperation of the respondent. It is simple to use and we do not feel that it requires special training. The three-point response format caused no problems; indeed, some participants readily understood the ordinal scale of never/no, sometimes and always/a lot, suggesting that they were familiar with such concepts. The option of presenting the scale first as a dichotomy of yes/no, and thereafter following an affirmative response as sometimes or always/a lot, appears to make the GDSLD accessible to most people with mild-to-moderate learning disability. Testretest data suggest consistency in responding, although we recommend that this should be repeated over a longer interval. The GDSCS can be completed in less than 5 min. Finally, it should be noted that the GDSLD and GDSCS are present state tools that gauge symptom level across a 1-week period. This was our intention, for two reasons. First, we were uncertain of the accuracy of obtaining patient report over longer intervals; and second, it permits use of the scales as measures both of process and outcome. In relation to the latter, a longer-term study using trials methodology is required to investigate change over time on the GDSLD and GDSCS.
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Clinical Implications and Limitations |
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LIMITATIONS
APPENDIX 1
Glasgow Depression Scale for people with a Learning Disability
(GDSLD)
Preparatory instructions
Hello. My name is.... I would like to talk to you about how you have
been feeling just recently. First, it would help if you could tell me
something you did last... [provide day of the week]/about a week ago.
[Provide prompts as necessary or ask a carer to identify an anchor
event.]
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I am going to ask you about how you have been feeling since [state anchor event last week]. Just between... and now, OK. There is no right or wrong answer I just want to know how you have been feeling. If I don't explain things well enough, just ask me to tell you what I mean. We will be using the pictures we looked at before. [Recap on the meanings of these.]
Administrative instructions
Each question should be asked in two parts. First, the participant is asked
to choose between a yes and no answer. Use the
symbols, if necessary. If their answer is no, the score in that
column (0 or 2) should be recorded. If their
answer is yes, they should be asked if that is
sometimes or always, and the score recorded as
appropriate. Some respondents will be able to use the three-point scale from
the start, others might learn the rules as you proceed.
Supplementary questions (italics) may be used if the primary question is not understood completely. If a response is unclear, ask for specific examples of what the participant means, or talk with them about their answer until you feel able to allocate it to a response category.
APPENDIX 2
Carer Supplement to the Glasgow Depression Scale for people with a
Learning Disability (GDSCS)
What is the name of the person you look after?
[UNK]
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[referred to as X in the following questions]
What is your relationship to X? [UNK]
The following questions ask about how you think X has been in the last week. There is no right or wrong answer. Please circle the answer you feel best describes X in the last week.
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Received for publication May 16, 2002. Revision received October 4, 2002. Accepted for publication October 21, 2002.
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