The process of diagnosing autism or Asperger syndrome can be difficult and complex. This article guides you through the systems and instruments you may need when carrying out a professional diagnosis.

Few of us like labels. However, they do have their uses. For children with autism and Asperger syndrome they have a necessary role. Without an accurate early diagnosis, children with autism spectrum disorders can be condemned to a life of inadequate provision, their special needs not tackled and their future lives devalued. For adults a correct, specific diagnosis is often sought and valued for the explanation it gives to what is a puzzling existence. The aim of diagnosis then is to:

  • enable understanding
  • provide guidance to teachers, parents and others on the nature of the child's condition and possible consequent problems
  • suggest ways of deploying effective management and teaching strategies.


Diagnosis of such a complex condition as autism is not easy and cannot be made by administering a blood test. Diagnosis requires close observation of behaviour as well as a developmental history from infancy. In particular, diagnosticians will be looking specifically for evidence of the triad of impairments and repetitive behaviour patterns. Since autism often co-exists with a number of other medical conditions this process is not as clear as it could be. Other learning disabilities and conditions can often throw the diagnostician off the track of a correct diagnosis. Even professionals close to autism find it difficult to recognise some individuals with the disorder (Larcombe 1998).

The need for early diagnosis

It is generally accepted that the earlier a true diagnosis is made the better for the child, the family and those involved around them. This is because effective strategies can only be employed if the true nature of a condition is known. It will be vital for the family to receive early support from outside, both to reduce stress within the family and to ensure that problem behaviours do not become entrenched in the child. Once established, such behaviours become increasingly more difficult to manage as the child grows older (Howlin 1998).

The need for early identification is made more urgent by the accumulating evidence that intensive early intervention in optimal educational settings results in improved outcomes in most young children with autism, including speech in 75% or more and significant increases in rates of developmental progress and intellectual performance (Dawson and Osterling 1997; Rogers 1996, 1998).

Early diagnosis also enables provision for family supports, reduction of family stress and delivery of appropriate medical care to the child (Cox et al 1999). Woolley et al (1989) showed that the way a diagnosis was presented to parents had a major impact on their acceptance of the situation, their long-term attitudes, stress and general coping strategies.

Early diagnosis is also vital to ensure that genetic counselling is made available to parents who may be considering or already have other children. There is an increased risk for the broader phenotype among siblings of children with an autistic spectrum disorder. Siblings, for example, might appear less affected than their brother or sister, but have real problems in areas such as social interaction or communication that early intervention could help to avoid becoming unmanageable.

Early screening

Autism is much common than once thought with up to half-a-million individuals affected in the UK alone. It is also more difficult to diagnose than, for example, cancer, diabetes or Down's syndrome. For these reasons it is necessary to adopt a screening approach first. It would be impossible at present for clinicians to test all children for a developmental disorder such as autism so the first step has to be to use simple screening instruments to identify those children most likely to be at risk of such problems.

By adding to the questions asked routinely by GPs and health visitors, some researchers have developed a useful screening instrument which seems to predict well the likelihood of a child being affected by an autistic spectrum disorder (Baird et al 2000; Baird et al 2001; Baron-Cohen et al 2000). The Checklist for Autism in Toddlers (CHAT) particularly assesses gaze monitoring, pretend play and proto-declarative pointing. Failure on these items is strongly associated with an autistic disorder.

Unlike the CHAT the Pervasive Developmental Disorders Screening Test - Stage 1 (Siegel 1998) rates positive as well as negative symptoms, and includes some questions concerning regression. It is a clinically derived parent questionnaire, and is divided into three stages, each of which is targeted at a different level of screening. It is aimed at use within the primary care setting with items designed incrementally from birth to 36 months of age. Its use of parental reports for stereotypic behaviours is probably more accurate than relying solely on observation as parents will have longer to observe and can see the behaviours in different settings. The PDDST-II is now available and covers three stages: a primary care screening test, child development clinic screening test and autism clinic severity screening test.

The Australian Scale for Asperger's Syndrome (Garnett and Attwood 1998) is a parent or teacher rating scale for high-functioning older children on the autism spectrum who have not been identified with an autistic spectrum disorder by school age. It consists of 24 questions rated with a score from 1 to 6, plus a checklist of ten additional 'yes' or 'no' behavioural characteristics. If the majority of questions are answered with a 'yes' and most of the ratings are between 2 and 6 a referral for diagnostic assessment would be indicated.

A great deal of valuable work is being done to bring down the age at which autism can be identified. Specific behaviours which distinguish infants with autism have been identified by using home videotapes (Osterling and Dawson 1994). The four behaviours which identified correctly over 90% of normal and autistic children, replicated in Mars, Mauk and Dowrick (1998), were:

  • eye contact
  • orientating to name being called
  • pointing
  • showing.


Osterling and Dawson (1999) also showed that 12-month-old infants with autism could be distinguished from their same-age peers with idiopathic learning disability. Such behaviours can be identified at younger ages (Brown et al 1998; Baranek 1999; Teitelbaum et al 1998). There is more work to do on the predictive utility of these findings but they suggest that autism will eventually be diagnosed reliably as early as 12 months or even younger.

Routine developmental surveillance

There are several screening and pre-screening tools and tests which can be used with children with possible autistic spectrum disorders to detect their particular developmental, cognitive, language and play abilities. In the USA the Denver-II (formerly the Denver Developmental Screening Test Revised; Frankenburg et al 1992) has traditionally been used for developmental screening for children up to six years of age. However, although easy to administer and score its validity has not been studied. It has been found to lack specificity (a significant number of normal children were misclassified as delayed) and to be insensitive (it missed a number of delayed children) (Glascoe et al 1992). The Revised Denver Pre-Screening Developmental Questionnaire (R-DPDQ; Frankenburg 1986) is designed to identify children who need further screening. Since it draws on the original version of the Denver Developmental Screening Test it too suffers from lack of sensitivity and specificity.

The Autism Screening Questionnaire (ASQ) is now known as the Social Communication Questionnaire (SCQ). It is an attempt to develop a reliable and valid screening instrument based on the current diagnostic criteria for autism. It uses the revised version of the ADI algorithm (Lord et al 1994) used for ICD-10 (World Health Organisation 1994) and DSM-IV (American Psychiatric Association 1994). Designed by Rutter and Lord (Berument et al 1999) to be used with all age groups, it is completed by the primary caregiver on individuals who might have an autistic spectrum disorder. The ASQ or SCQ consists of 40 questions, based on the ADI-R but modified to be understandable by parents without further explanation. It is available in two versions, one for children under six years of age and the other for individuals of six years plus. The ASQ or SCQ was found to be a highly effective screening instrument for children aged four and above. Of course, like any questionnaire, it cannot provide individual diagnosis. 

Standardised developmental screening instruments with acceptable psychometric properties include:

  • The Ages and Stages Questionnaire, 2nd edition, ASQ; Bricker and Squires 1994, 1999; Squires, Bricker and Potter 1997). This uses parental report for children up to three years. It is important to recognise that parents are usually correct in their concerns about their child's development (Glascoe, 1994, 1997, 1998; Glascoe and Dworkin 1995). There are versions for other age ranges. Although well standardised and validated it is brief and is more used as a pre-screening tool.
  • BRIGANCE Screens (Brigance 1986; Glascoe 1996) contain seven separate forms, one for each 12-month age range from 21 to 90 months of age. Available in English and Spanish, it takes ten minutes to administer and taps key developmental and early academic skills, including speech-language; fine and gross motor skills; graphomotor development; and general knowledge at the younger ages and reading and mathematics at older ages.
  • The Child Development Inventories (Ireton 1992; Ireton and Glascoe 1995) include three separate measures covering birth to 72 months of age and are completed by parental report in about five to ten minutes. The CDIs screen for language, motor, cognitive, preacademic, social, self-help, behaviour and health problems and have good specificity and excellent sensitivity. For parents with limited English, items can be directly administered to children.
  • The Parents' Evaluation of Developmental Status (PEDS; Glascoe 1998) helps providers elicit and interpret parents' concerns. It assigns probabilities of delays and disabilities to the various types of concerns, enabling clinicians to make evidence-based decisions, provide counselling and reassure parents. Parents have to answer ten questions written in plain English or Spanish and these can be scored and interpreted by clinicians in about two minutes. PEDS is well validated and standardised and research has shown that parents are likely to be accurate.
  • Bayley scales II (Bayley 1993) is a revision of the classic Bayley scales of infant development designed for children from 1-42 months of age. In clinical settings these scales have been used to identify children with developmental delays or those suspected of being at risk. It can be administered over one or two sessions and takes between 45 and 60 minutes to administer. The three scales used are:
    • mental, includes evaluation of sensory/perceptual acuities, memory, learning and problem solving, vocalisation, and early communicative functioning
    • motor, includes evaluation of degree of body control and fine manipulation skills
    • behaviour, includes measures of attention and arousal, orientation and engagement and emotional regulation.


    The Wechsler pre-school and primary scale of intelligence, revised edition (WPPSI-R) (Wechsler 1990) is a well-established method of assessing abilities of children between three and seven years of age. It has been Anglicised and metricated for use in the UK and individual administration takes about 60 minutes. 

    The RED FLAGS for autism

    What should health professionals look out for when parents express concerns? 

    Communication concerns

    • Does not respond to his/her name
    • Cannot tell me what s/he wants
    • Language is delayed
    • Doesn't follow directions
    • Appears deaf at times
    • Seems to hear sometimes but not at others
    • Doesn't point or wave goodbye
    • Used to say a few words, but now doesn't.

    Social concerns

    • Doesn't smile socially
    • Seems to prefer to play alone
    • Gets things for him/herself
    • Is very independent
    • Does things 'early'
    • Has poor eye contact
    • Is in his/her own world
    • Tunes us out
    • Is not interested in other children.

    Behavioural concerns

    • Tantrums
    • Is hyperactive/unco-operative/oppositional
    • Doesn't know how to play with toys
    • Gets stuck on things regularly
    • Toe walks
    • Has unusual attachments to toys
    • Lines things up
    • Is oversensitive to certain textures or sounds
    • Has odd movement patterns.

    Absolute indications for immediate further evaluation

    • No babbling by 12 months
    • No gesturing (pointing, waving, bye-bye, etc) by 12 months
    • No single words by 16 months
    • No two-word spontaneous (not just echolalic) phrases by 24 months
    • ANY loss of ANY language or social skills at ANY age.


    Reproduced with the permission of the author and publisher from Filipek et al. 1999

    A fully inclusive society would ensure that all children were regularly and proactively screened for developmental disorders throughout infancy, the early school years and even beyond if concerns are raised.

    International diagnostic systems

    The main international diagnostic classifications are the International Classification of Diseases 10th edition ICD-10 (World Health Organisation 1992) and the Diagnostic and Statistical Manual 4th edition DSM-IV (American Psychiatric Associaltion 1994). Each have included autism since the late 1970s. The ICD-10 criteria for autism can be found in the ICD-10 Classification of Mental and Behavioural Disorders in pdf format at http://www.who.int/classifications/icd/en/GRNBOOK.pdf  The criteria are in section F84.0 and focus on:

    • abnormal communication
    • abnormal social development
    • ritualistic and stereotyped behaviour and resistance to change.


    Asperger syndrome, by contrast, did not reach the ICD or DSM classifications until the 1990s and there is still confusion over the diagnostic criteria for Asperger syndrome and whether and/or how it differs from high functioning autism. For example, DSM-IV excludes the diagnosis of Asperger syndrome if the child also fulfils the criteria for autism, whereas ICD-10 is more equivocal.

    Within the areas identified by ICD-10, however, there is huge variability. All people with autism will bring their individual characteristics to bear. The condition may, therefore, appear different in the same child at different ages, and with different cognitive levels in children. Because of this variability and also because it is difficult to disentangle problems in social interaction, communication and ritualistic or obsessive behaviours, it is best to use tools or instruments that specifically test for the presence of autistic symptomatology (Howlin 1998). In clinical practice individuals with a mixture of features of autism and Asperger syndrome are more common than either of the pure syndromes. It is more useful to classify on level of ability than on theoretical diagnostic subgroups.

    Diagnostic instruments

    There are two main methods for achieving this. The first is to make a systematic collection of facts and select from them to make a diagnosis and recommendations for care. This is the approach adopted by Lorna Wing, Judith Gould and colleagues at The National Autistic Societys Lorna Wing Centre for Autism, formerly The Centre for Social and Communication Disorders. They have used such an approach - the Handicaps and Behaviour Schedule (HBS) - since the late 1970s (Wing and Gould 1978). It covers many aspects of behaviour from infancy onwards. The HBS has now been developed further into the Diagnostic Interview for Social and Communication Disorders (DISCO), which has undergone evaluation in the UK and Sweden and is available to those who have followed the required training course. The algorithms used for the DISCO have already been used to compare the ICD-10 criteria for Asperger syndrome with those suggested by Gillberg (Leekam et al 2000). The Autistic Diagnostic Interview - Revised (ADI-R) developed by Lord Rutter and Le Couteur (1994) takes a similar approach but is geared towards diagnosing typical autism for research purposes. The 3Di, the Developmental, Dimensional and Diagnostic Interview, is another diagnostic instrument which uses computerised analysis of answers to interview questions (Skuse et al 2004).

    The other method is to take the common features of autistic behaviour and count them to determine whether a person can be diagnosed within the spectrum. This more mechanical approach is taken by various checklists such as the Gilliam Autism Rating Scale (Gilliam 1998). This is a checklist designed to be used by parents, teachers, and professionals to help to identify and estimate the severity of symptoms of autism in individuals between the ages of three and 22 years. It is based on DSM-IV (American Psychiatric Association 1994) and groups items into four subtests -stereotyped behaviours, communication, social interaction and an optional test which describes development in the first three years of life.

    Due to the demands made on busy clinicians, there have been a number of attempts to produce instruments which would detect autism more speedily than the diagnostic instruments above. These include the Childhood Autism Rating Scale (Schopler, Reichler and Renner 1988). This is a 15-item structured interview and observation instrument suitable for use with children over 24 months of age. Each item uses a seven-point rating scale to indicate the degree to which the child's behaviour differs from an age-appropriate norm. It also distinguishes the degree of autism. It takes about 30-45 minutes to administer and is widely regarded as a reliable tool for diagnosing autism.

    The Parent Interview for Autism (Stone and Hogan 1993) is a structured interview containing 118 items, arranged in 11 dimensions assessing various aspects of social behaviour, communicative functioning, repetitive activities and sensory behaviours. It is designed to obtain diagnostically relevant information from parents of young children suspected of having autism and takes around 45 minutes to administer. It has good internal consistency and reliability and has demonstrated concurrent validity with both CARS (Schopler, Reichler and Renner 1988) and DSM-IV (American Psychiatric Association 1994).

    Other examples are the Autism Behaviour Checklist (Krug, Arick and Almond 1980) and the Behavioural Rating Instrument for autistic and other atypical children (Ruttenberg et al 1977).

    These cannot, however, be used in the same way as the diagnostic instruments but show only whether children might fall within the autistic spectrum. Valuable as this is, diagnosis can only be clarified by experienced clinical observation, together with a detailed and systematic interview (Howlin 1998). Checklists, by themselves, tend to miss many of the odder manifestations within the autism spectrum.

    Attempts have also been made to provide structured observational tools. These help to make the most of the sometimes limited time clinicians have available to observe children. The Autism Diagnostic Observation Schedule (ADOS) (Lord et al 1989) spawned a further version, the Pre-Linguistic ADOS (Di Lavore Lord and Rutter 1995) but is now used in a generic version ADOS-G (Lord et al 1996). It attempts through a series of structured tasks to assess the child's social and communicative functioning. The tasks include constructional and turn-taking activities, imitation, the ability to tell a story, imaginative toy play, gesture and conversational skills. The ADOS-G takes around 20-40 minutes to complete but can provide more information than would have been gained by informal observation. At the very least a clinician should seek to observe a child away from the time of formal testing or routine questioning. Like the ADI-R, the ADOS-G is used widely in autism research protocols.

    Another measure intended to be administered to children aged between 24 and 35 months by various early childhood professionals is the Screening Tool for Autism in Two-year-olds (Stone 1998a, 1998b). This tool is still in development but is designed specifically to differentiate autism from other developmental disorders. The tool is administered through a 20-minute play interaction involving 12 activities. These sample three areas: play (both pretend and reciprocal social play), motor imitation and non-verbal communicative development. There is a manual with clear instructions for administration and scoring. The pilot study showed very strong sensitivity and specificity.

    Finally Filipek et al (1999) recommend that children with autistic spectrum disorders and developmental delays should have formal audiological evaluation, screening for lead poisoning, and adaptive behaviour, sensorimotor and neuropsychological assessment, as well as metabolic and electrophysiologic testing. They also recommend an assessment of family functioning to determine parents' level of understanding of their child's condition in order to offer appropriate counselling and education.

    Appendix 1: contact information for instruments

    Ages and Stages Questionnaire (ASQ), 2nd ed.
    Paul H. Brookes Publishing Co., PO Box 10624, Baltimore, MD 21285, USA. Tel: +1 800 638 3775; Fax: +1 410 337 8539

    Australian Scale for Asperger's syndrome / M.S. Garnett and A. J. Attwood. 1998.
    In: Attwood, T. ed. Asperger's syndrome: a guide for parents and professionals. London: Jessica Kingsley, pp17-20

    Autism Diagnostic Interview Revised, (ADI-R), Autism Diagnostic Observation Schedule Generic, (ADOS-G), Social Communication questionnaire, (SCQ) .
    Materials and training videos available from:
    The Test Agency Ltd, Burgner House, 4630 Kingsgate, Oxford Business Park South, Oxford, OX4 2SU. Tel: +44 (0)1865 402900; Fax: +44 (0)1865 402888. Website: www.hogrefe.co.uk

    ADI-R and ADOS-G are also available from:
    Western Psychological Services, 12031 Wilshire Blvd., Los Angeles, CA 90025-1251,U.S.A. Tel: +1 800 648 8857 (N. America) or  +1 310 478 2061; Fax: +1 310 478 7838.
    Website: www.wpspublish.com  

    BRIGANCE screens
    Curriculum Associates, Inc., PO Box 2001, North Billerica, MA 01862-0901, USA. Tel: +1 800 225 0248; Fax: + 1 800 366 1158; Email: cainfo@curricassoc.com

    Checklist for Autism in Toddlers (CHAT)
    Sally Wheelwright, Autism Research Centre, University of Cambridge, Douglas House, !8b Trumpington Road, Cambridge, UK, CB2 2AH. Tel: +44 (0)1223 746057; Fax: +44 (0)1223 746033; Email: sjw18@cam.ac.uk 

    Child Development Inventories (CDIs)
    Behavior Science Systems, Box 580274, Minneapolis, MN 55458, USA. Tel: +1 612 929 6220

    Childhood Autism Rating Scale
    Winslow Press, Telford Road, Bicester, Oxon., UK, OX6 0TS; Tel +44 (0)1869 244644. Website: www.winslow-press.co.uk

    Or from Harcourt Assessment, Halley Court, Jordan Hill, Oxford, OX2 8EJ; Tel: +44(0)1865 888188. Website: www.harcourt-uk.com

    Or from Western Psychological Services, 12031 Wilshire Bvd., LA, CA 90025-1251, USA. Tel: +1 800 648 8857 (N. America) or +1 310 478 2061; Fax: + 1 310 478 7838. Website: www.wpspublish.com

    Diagnostic Interview for Social and Communication Disorders (DISCO)
    Dr Lorna Wing and Dr Judith Gould, The NAS Lorna Wing Centre for Autism, Elliot House, 113 Masons Hill, Bromley, UK, BR2 9HT. Tel: +44 (0)20 8466 0098; Fax: +44 (0)20 8466 0118; Email: elliot.house@nas.org.uk

    Gilliam Autism Rating Scale
    NFER-Nelson, The Chiswick Centre, 414 Chiswick High Road, London, W4 5TF. Tel: +44 (0)20 8996 8444; fax: +44 (0)20 8996 8444; email: information@nfer-nelson.co.uk. Website: www.nfer-nelson.co.uk

    Parents' Evaluation of Developmental Status (PEDS)
    Ellsworth and Vandermeer Press LLC, P.O.Box 68164, Nashville, TN 37206, USA. Tel: +1 615 226 4464; Fax: +1 615 227 0411. Website: www.pedstest.com
    The test can be completed online for a small charge: www.forepath.org

    The Parent Interview for Autism (PIA)
    The Screening Tool for Autism in Two-year-olds (STAT)
    Wendy Stone, Vanderbilt TRIAD, Medical Center South, Room 415, 2100 Pierce Avenue, Nashville TN37232-3573, USA. Tel: +1 615 936 0280; Email: wendy.stone@vanderbilt.edu

    Pervasive Developmental Disorders Screening Test (PDDST)
    Bryna Siegel, Langley Porter Psychiatric Institute, Box CAS, University of California, San Francisco, CA 94143-0984, USA. Tel: +1 415 476 7385; Fax: +1 415 476 7160.

    3Di
    Richard Warrington, BBSU, Institute of Child Health, 30 Guilford Street, London WC1N 1EH; TEl: 01308 485431; email: 3Di@ich.ucl.ac.uk     

    Appendix 2: glossary of terms

    Audiological evaluation: an evaluation conducted to test the hearing of an individual who appears deaf, either temporarily or permanently. There are two broad categories of hearing assessment available: behavioural and electrophysiological. For children suspected of developmental disorders behavioural assessment, including pure formal tone audiometry, should be performed by an experienced audiologist. Brainstem auditory evoked potentials will only be necessary if the initial test is equivocal, suboptimal, or suggests central nervous system abnormality.

    Broad autism phenotype: characteristics that are qualitatively similar but milder than those that define autism - social and communication deficits and stereotyped, repetitive behaviours - which show familial aggregation in families with a member or members with autism.

    Graphomotor development: those fine motor skills associated with handwriting and drawing.

    Idiopathic learning disability: idiopathic means a disorder of unknown cause.

    Proto-declarative pointing: this type of pointing is to declare an interest in something as opposed to proto-imperative pointing which is used for requesting something. Proto-declarative pointing is deficient in children with autistic spectrum disorders.

    Triad of impairments: autistic spectrum disorders are characterised by impairments in social interaction, social communication and social imagination which can occur in varying degrees of severity. This triad is generally accompanied by a limited, narrow, repetitive pattern of activities.

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    Further reading

    Baron-Cohen, S. et al. (2001). The Autism-Spectrum Quotient (AQ): evidence from Asperger syndrome/high-functioning autism, males and females, scientists and mathematicians. Journal of Autism and Developmental Disorders, 31(1), pp5-17

    Bryson, S., Zwaigenbaum, L. & Roberts, W. (2004). The early detection of autism in clinical practice. Paediatrics and Child Health, 9(4), pp219 -221. Available to download from www.pulsus.com/Paeds/09_04/brys_ed.htm

    Campbell, J.M. (2005). Diagnostic assessment of Aspergers disorder: a review of five third-party rating scales. Journal of Autism and Developmental Disorders, 35(1), pp25-35

    Chandler, S. et al. (2002). Developing a diagnostic and intervention package for 2- to 3-year-olds with autism: outcomes of the Frameworks for Communication approach. Autism, 6(1), pp47-69

    Charman, T. & Baird G. (2002). Practitioner review: diagnosis of autism spectrum disorder in 2- and 3-year-old children. Journal of Child Psychology and Psychiatry and allied disciplines, 43(3), pp289-305

    de Bildt, A. et al. (2004). Interrelationship between Autism Diagnostic Observation Schedule-Generic (ADOS-G), Autism Diagnostic Interview-Revised (ADI-R), and the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) Classification in Children and Adolescents with Mental Retardation. Journal of Autism and Developmental Disorders, 34(2), pp129-137

    Gillberg, C. et al. (2002). The Asperger Syndrome (and high-functioning autism) Diagnostic Interview (ASDI): a preliminary study of a new structured clinical interview. Autism, 5(1), pp57-66

    Klin, A. et al. (2005). Three diagnostic approaches to Asperger syndrome: implications for research. Journal of Autism and Developmental Disorders, 35(2), pp221-234

    McConachie, H. et al. (2005) Can a diagnosis of Asperger syndrome be made in very young children with suspected autism spectrum disorder? Journal of Autism and Developmental Disorders, 35(2), pp167-176

    Perry J., et al. (2005). Multi-site study of the Childhood Autism Rating Scale (CARS) in five clinical groups of young children. Journal of Autism and Developmental Disorders, 35(5), pp625-634

    Stone, W. L. et al. (2004). The Parent Interview for Autism-Clinical Version (PIA-CV): A measure of behavioral change for young children with autism. Autism, 7(1), pp9-30

    Woodbury-Smith, M. et al. (2005). Aspergers syndrome: a comparison of clinical diagnoses and those made according to the ICD-10 and DSM-IV. Journal of Autism and Developmental Disorders, 35(2), pp235-240