Changing terminology for children's language disorders: reflections on special issue of Perspectives of the ASHA Special Interest Groups

In 2016-7, I joined with expert colleagues to try to tackle the thorny issue of terminology for children who had difficulties speaking or understanding in their native language. This was incredibly challenging: we had a panel of 57 experts, moderated by Maggie Snowling and me, engage in a Delphi process, whereby we iteratively rated and commented on statements to do with identification and diagnosis to converge on a set of recommendations (Bishop et al., 2016; 2017). There was substantial disagreement between experts, who came from a range of disciplines and nationalities, but the one thing we agreed upon was that the current situation – of a plethora of different terms being used with various meanings – was doing a grave disservice to families and their children affected by language problems. There was a lack of recognition of language problems among professionals and the general public, as well as a paucity of research relative to other conditions of similar severity and prevalence. Eventually we converged on a recommendation that the term 'Developmental Language Disorder' (DLD) should be used to describe children with persistent problems with language expression or reception that had no obvious cause, and that impacted on everyday life.

Publication of the 2017 recommendations had considerably greater impact than I had anticipated, thanks to the generally enthusiastic take-up of the new terminology, which has been adopted by professional organisations in the UK, Ireland and Australia. A brief summary of the salient points was written by Susan Ebbels for the Royal College of Speech and Language Therapists.

Following the publication of the CATALISE papers, big changes have happened just in a couple of years:

• The terminology has stimulated development of grassroots advocacy, with campaigns to promote awareness of DLD adopting ingenious and innovative methods to publicise events. See e.g. here.
• The DLD label has raised awareness that this is a life-long condition*. Adults with DLD have started to talk about their experiences on social media (e.g. here). 
• Figures on terminology from Web of Science show that DLD is starting to overtake the term 'Specific Language Impairment' in published papers.
   



Figure 1: N publications with full term 'Specific Language Impairment' or 'Developmental Language Disorder' in the Topic field; data from Web of Science


Nevertheless, despite these positive developments, not everyone has been convinced that adoption of DLD is a good thing. This is not surprising: a couple of years ago, I reflected on some of the reasons why this particular topic is a terminological minefield (Bishop, 2017). It is difficult to balance the pros and cons of new terminology, especially when one is dealing with a condition that is heterogeneous, changes with age, can co-occur with many other problems, and is of relevance to several professions with very different perspectives, in particular speech-language therapists/pathologists, educators and medics.

Resistance to new terminology appears to be strongest in the USA, with the American Speech-Language-Hearing Association being particularly cautious about replacing the term Specific Language Impairment with DLD. This week they published a set of papers by individuals with different viewpoints on the topic, and reading through this I was reminded of many of the debates we had in the course of our Delphi exercises. The special issue includes a  tutorial overview by Karla McGregor and colleagues (McGregor et al., 2020), who summarise the background to the CATALISE project, and subsequent developments. They are supportive of DLD, not least because of the way the new terminology has boosted the profile of children's language problems and stimulated greater efforts towards advocacy. But we need to take seriously the concerns of those who have doubts.

Two authors in particular, Larry Leonard and Mabel Rice, were concerned that if we adopt DLD as the preferred term, decades of research on SLI would be ignored and ultimately forgotten. Both of them have made major lifetime contributions to the field, and so their concerns are understandable. It is vital that we heed Larry's advice (Leonard, 2020) to ensure that we include the search term SLI as well as DLD when drawing together relevant literature, to ensure valuable work from previous decades is not lost.

A related issue is that, although they overlap, SLI and DLD are not identical. In general, DLD is a more inclusive term, as it does not require that nonverbal IQ is 85 or over (although it does exclude cases of intellectual disability**), and it is compatible with the presence of other neurodevelopmental disorders, especially developmental co-ordination disorder and attention-deficit-hyperactivity disorder. Rice (2020) remains strongly opposed to the use of DLD, mainly because this would entail including children with nonverbal IQs below 85 (who were termed cases of nonspecific language impairment, or NLI, in a big epidemiological study, the Iowa study). Yet this stance is hard to reconcile with her view that nonverbal ability is independent of language. She spends several paragraphs presenting evidence that it is possible to have low nonverbal ability and good language, or high nonverbal ability and poor language, culminating in the statement: 'The common assumption that children with SLI are not very smart is unwarranted, as is the assumption that all children with strong language aptitude are smart.' It is unclear to whom she is referring as making this 'common assumption'. A major reason why the CATALISE group decided to drop 'cognitive referencing' in defining DLD was because the bivariate distribution of nonverbal IQ and language demonstrates rather a weak association – just as she claims - but this makes it clear that any division into those above and below an IQ threshold is arbitrary (see Figure 2). Just to be absolutely clear, in proposing we do away with nonverbal IQ criteria for DLD, the CATALISE consortium were not saying that children with SLI are 'not very smart'. We were saying that they key thing is what your language is like, and that nonverbal ability is largely irrelevant when making that judgement.

Figure 2: Language composite measure plotted against non‐verbal IQ for 603 eight‐year‐old children in the Iowa study. Figure from Reilly et al (2014). Blue points correspond to SLI, and green points to NLI. NB Axes resized to address criticism by Rice (2020), who found the scaling misleading.

Rice goes on to argue that we need to study children's mastery of specific grammatical markers over time to get a precise measure of children's language in SLI, yet she then goes on to present data showing that children with NLI are also identified by low scores on those markers. Although she claimed a difference in language profiles, this was not evident from the data she presented, and in general, most studies that have looked for qualitative differences between NLI and SLI have failed to find these (see also further evidence from McGregor et al, 2020). Rice maintains that only by sticking with SLI would we find sufficiently clear findings to advance our understanding, and that if we adopt less precise categories, this will lead to muddying of the waters and less replicable results. I regard this as a hypothesis that can be tested, but for which there is currently no good evidence. In fact, it was the failure to find such evidence in my own studies 25 years ago that led me to start to question the construct of SLI (Bishop, 1994).

Larry Leonard makes the sensible suggestion that if we study DLD we should also provide data on which children would meet the more restrictive definition of SLI:  this would, in fact, allow us to test Rice's hypothesis. The best way to do this, and to build on prior studies with SLI would be to make raw data open (see Meyer, 2018), so that results can be analysed to investigate the extent to which findings depend on levels of nonverbal ability, attention, motor skills and so on. There is already precedent for this with the EpiSLI database from the Iowa study (Tomblin, 2010) – this includes data on children who would meet broader DLD criteria as well as more selective SLI cases. This way we could investigate empirically the impact of the choice of criteria, rather than just asserting that one classification approach is better than the other.

I turn next to the other commentary that is predominantly negative about a change of criteria to DLD, that by Murza and Ehren (2020). Their perspective is diametrically opposed to that of Rice. They explain that for speech-language pathologists (SLPs) working in the school system, there is a mismatch between what is taught in their university courses (including diagnosis of SLI) and what they experience in the classroom. There were some parallels here with the views of education experts on the CATALISE panel, some of whom felt the whole debate about labels was irrelevant, and would empathise with the view that: 'No matter the label, students should receive the services they need, and no label should drive services'. But, as Murza and Ehren recognise, labels are needed to demonstrate eligibility for services, and in the USA, this is determined by the Individuals with Disabilities Education Act (IDEA), which has its own set of labels: these don't include either SLI or DLD. I felt a sense of despair coming through from this article, as the authors documented the confusing array of possible terms they could use, each of which had an operational definition, but with that definition varying from one state to another. The impression was that SLPs in US education are up against a massive, unbending bureaucracy that they had to negotiate in order to deliver services to a subset of the children that might benefit from them. In principle, yes, it would be nice to have some consistent terminology that mapped on to the population they were serving, but their conclusion was that they lacked the time, money, energy and focus to embark on a campaign to adopt new labels. This was a considerably more sober and downbeat chapter than that of Rhea Paul, who regarded DLD as potentially compatible with IDEA criteria, and a useful focus for advocacy efforts. 

When discussing relevance of labels for SLP practitioners, another issue concerned insurance eligibility. Karla McGregor reported that she had been told by an insurer: 'If a child just isn't talking or not talking clearly - it is not covered'. The authors also noted a common concern that the term Developmental would be interpreted by insurers, and perhaps others, as implying that the condition would improve of its own accord. But SLPs should not take these kinds of responses lying down: it is grossly inequitable if insurers are willing to pay for a condition such as ADHD or Developmental Co-ordination Disorder, but not for speech-language therapy for a child with DLD. The arguments can and should be made, and it is hoped that the growing awareness of, and advocacy for DLD will empower US SLPs to be more proactive in demanding that children with language disorders are taken seriously and given the support they need.

* Damian Quinn, a man with DLD, has written an autobiography. The timing in relation to CATALISE is probably co-incidental, but this will help with growing awareness that children with DLD do not disappear when they become adults!

** The introductory article for the special issue stated that DLD is used for children 'with or without intellectual disability'. This is wrong. Where the child meets criteria for intellectual disability, the diagnosis would be Language Disorder associated with Intellectual Disability.

P.S. (24 Feb 2020). All the materials from the CATALISE project, including anonymised ratings and comments from the 57 panel members, are available on Open Science Framework.

References

 Bishop, D. V. M. (1994). Is specific language impairment a valid diagnostic category? Genetic and psycholinguistic evidence. Philosophical Transactions of the Royal Society, series B, 346, 105-111. 

Bishop, D. V. M. (2017). Why is it so hard to reach agreement on terminology? The case of developmental language disorder (DLD). International Journal of Language & Communication Disorders, 52(6), 671-680. doi:10.1111/1460-6984.12335

Bishop, D. V. M., Snowling, M. J., Thompson, P. A., Greenhalgh, T., & CATALISE Consortium. (2016). CATALISE: a multinational and multidisciplinary Delphi consensus study. Identifying language impairments in children. . PLOS One, 11(7), e0158753. doi:doi:10.1371/journal.pone.0158753

Bishop, D. V. M., Snowling, M. J., Thompson, P. A., Greenhalgh, T., & CATALISE Consortium. (2017). Phase 2 of CATALISE: a multinational and multidisciplinary Delphi consensus study of problems with language development: Terminology. Journal of Child Psychology and Psychiatry, 58(10), 1068-1080. doi:10.1111/jcpp.12721

Leonard, L. B. (2020). A 200-year history of the study of childhood language disorders of unknown origin: changes in terminology. Perspectives of the ASHA Special Interest Groups, 5(1), 6-11. doi:https://doi.org/10.1044/2019_PERSP-SIG1-2019-0007

McGregor, K. K., Goffman, L., Owen Van Horne, A., Hogan, T. P., & Finestack, L. H. (2020). Developmental Language Disorder: Applications for advocacy, research, and clinical service. Perspectives of the ASHA Special Interest Groups, 5(1), 38-46. doi:https://doi.org/10.1044/2019_PERSP-19-00083

Meyer, M. N. (2018). Practical tips for ethical data sharing. Advances in Methods and Practices in Psychological Science. doi:https://doi.org/10.1177/2515245917747656

Murza, K. A., & Ehren, B. J. (2020). Considering the language disorder label debate from a school speech-language pathology lens. Perspectives of the ASHA Special Interest Groups, 5(1), 47-54. doi:https://doi.org/10.1044/2019_PERSP-19-00077

Paul, R. (2020). Children's language disorders: What's in a name. Perspectives of the ASHA Special Interest Groups, 5(1), 30-37. doi:https://doi.org/10.1044/2019_PERS-SIG1-2019-0012

Rice, M. (2020). Clinical lessons from studies of children with Specific Language Impairment. Perspectives of the ASHA Special Interest Groups, 5(1), 12-29. doi:https://doi.org/10.1044/2019_PERSP-19-00011

Reilly, S., Tomblin, B., Law, J., McKean, C., Mensah, F. K., Morgan, A., . . . Wake, M. (2014). Specific language impairment: a convenient label for whom? International Journal of Language & Communication Disorders, 49(4), 416-451. doi:10.1111/1460-6984.12102

Tomblin, J. B. (2010). The EpiSLI database: a publicly available database on speech and language. Lang Speech Hear Serv Sch, 41(1), 108-117.

Developmental language disorder: the need for a clinically relevant definition

There's been debate over the new terminology for Developmental Language Disorder (DLD) at a meeting (SRCLD) in the USA. I've not got any of the nuance here, but I feel I should make a quick comment on one issue I was specifically asked about, viz:

As background: the field of children's language disorders has been a terminological minefield. The term Specific Language Impairment (SLI) began to be used widely in the 1980s as a diagnosis for children who had problems acquiring language for no apparent reason. One criterion for the diagnosis was that the child's language problems should be out of line with other aspects of development, and hence 'specific', and this was interpreted as requiring normal range nonverbal IQ (nviq).

The term SLI was never adopted by the two main diagnostic systems -WHO's International Classification of Diseases (ICD) or the American Psychiatric Association's Diagnostic and Statistical Manual (DSM), but the notion that IQ should play a part in the diagnosis became prevalent.

In 2016-7 I headed up the CATALISE project with the specific goal of achieving some consensus about the diagnostic criteria and terminology for children's language disorders: the published papers about this are openly available for all to read (see below). The consensus of a group of experts from a range of professions and countries was to reject SLI in favour of the term DLD.

Any child who meets criteria for SLI will meet criteria for DLD: the main difference is that the use of an IQ cutoff is no longer part of the definition. This does not mean that all children with language difficulties are regarded as having DLD: those who meet criteria for intellectual disability, known syndromes or biomedical conditions are treated separately (see these slides for summary).

The tweet seems to suggest we should retain the term SLI, with its IQ cutoff, because it allows us to do neatly controlled research studies. I realise a brief, second-hand tweet about Rice's views may not be a fair portrayal of what she said, but it does emphasise a bone of contention that was thoroughly gnawed in the discussions of the CATALISE panel, namely, what is the purpose of diagnostic terminology? I would argue its primary purpose is clinical, and clinical considerations are not well-served by research criteria.

The traditional approach to selecting groups for research is to find 'pure' cases - quite simply, if you include children who have other problems beyond language (including other neurodevelopmental difficulties) then it is much harder to know how far you are assessing correlates or causes of language problems: things get messy and associations get hard to interpret. The importance of controlling for nonverbal IQ has been particularly emphasised over many years: quite simply, if you compare language-impaired vs comparison (typically-developing, or td) children on a language or cognitive measure, and the language-impaired group has lower nonverbal ability, then it may be that you are looking at a correlate of nonverbal ability rather than language. Restricting consideration to those who meet stringent IQ criteria to equalise the groups is one way of addressing the issue.

However, there are three big problems with this approach:

1. A child's nonverbal IQ can vary from time to time and it will depend on the test that is used. However, although this is problematic, it's not the main reason for dropping IQ cutoffs; the strongest arguments concern validity rather than reliability of an IQ-based approach.

2. The use of IQ-cutoffs ignores the fact that pure cases of language impairment are the exception rather than the rule. In CATALISE we looked at the evidence and concluded that if we were going to insist that you could only get a diagnosis of DLD if you had no developmental problems beyond language, then we'd exclude many children with language problems (see also this old blogpost). If our main purpose is to get a diagnostic system that is clinically workable, it should be applicable to the children who turn up in our clinics - not just a rarefied few who meet research criteria. An analogy can be drawn with medicine: imagine if your doctor identified you with high blood pressure but refused to treat you unless you were in every other regard fit and healthy. That would seem both unfair and ill-judged. Presence of co-occurring conditions might be important for tracking down underlying causes and determining a treatment path, but it's not a reason for excluding someone from receiving services.

3. Even for research purposes, it is not clear that a focus on highly specific disorders makes sense. An underlying assumption, which I remember starting out with, was the idea that the specific cases were in some important sense different from those who had additional problems. Yet, as noted in the CATALISE papers, the evidence for this assumption is missing: nonverbal IQ has very little bearing on a child's clinical profile, response to intervention, or aetiology. For me, what really knocked my belief in the reality of SLI as a category was doing twin studies: typically, I'd find that identical twins were very similar in their language abilities, but they sometimes differed in nonverbal ability, to the extent that one met criteria for SLI and the other did not. Researchers who treat SLI as a distinct category are at risk of doing research that has no application to the real world.

There is nothing to stop researchers focusing on 'pure' cases of language disorder to answer research questions of theoretical interest, such as questions about the modularity of language. This kind of research uses children with a language disorder as a kind of 'natural experiment' that may inform our understanding of broader issues. It is, however, important not to confuse such research with work whose goal is to discover clinically relevant information.

If practitioners let the theoretical interests of researchers dictate their diagnostic criteria, then they are doing a huge disservice to the many children who end up in a no-man's-land, without either diagnosis or access to intervention. 

References

Bishop, D. V. M. (2017). Why is it so hard to reach agreement on terminology? The case of developmental language disorder (DLD). International Journal of Language & Communication Disorders, 52(6), 671-680. doi:10.1111/1460-6984.12335

Bishop, D. V. M., Snowling, M. J., Thompson, P. A., Greenhalgh, T., & CATALISE Consortium. (2016). CATALISE: a multinational and multidisciplinary Delphi consensus study. Identifying language impairments in children. PLOS One, 11(7), e0158753. doi:10.1371/journal.pone.0158753

Bishop, D. V. M., Snowling, M. J., Thompson, P. A., Greenhalgh, T., & CATALISE Consortium. (2017). Phase 2 of CATALISE: a multinational and multidisciplinary Delphi consensus study of problems with language development: Terminology. Journal of Child Psychology and Psychiatry, 58(10), 1068-1080. doi:10.1111/jcpp.12721

Prisons, developmental language disorder, and base rates

There's been some interesting discussion on Twitter about the high rate of developmental language disorder (DLD) in the prison population. Some studies give an estimate as high as 50 percent (Anderson et al, 2016), and this has prompted calls for speech-language therapy services to be involved in the working with offenders. Work by Pam Snow and others has documented the difficulties of navigating the justice system if your understanding and ability to express yourself are limited.

This is important work, but I have worried from time to time about the potential for misunderstanding. In particular, if you are a parent of a child with DLD, should you be alarmed at the prospect that your offspring will be incarcerated? So I wanted to give a brief explainer that offers some reassurance.

The simplest way to explain it is to think about gender. I've been delving into the latest national statistics for this post, and found that the UK prison population this year contained 82,314 men, but a mere 4,013 women. That's a staggering difference, but we don't conclude that because most criminals are men, therefore most men are criminals. This is because we have to take into account base rates: the proportion of the general population who are in prison. Another set of government statistics estimates the UK population as around 64.6 million, about half of whom are male, and 81% are adults. So a relatively small proportion of the adult population is in prison, and the numbers of non-criminal men vastly outnumber the number of criminal men.

I did similar sums for DLD, using data from Norbury et al (2016) to estimate a population prevalence of 7% in adult males, and plugging in that relatively high figure of 50% of prisoners with DLD. The figures look like this.

Numbers (in thousands) assuming 7% prevalence of DLD and 50% DLD in prisoners*

As you can see, according to this scenario, the probability of going to prison is much greater for those with DLD than for those without DLD (2.24% DLD vs 0.17% without DLD), but the absolute probability is still very low – 98% of those with DLD will not be incarcerated.

The so-called base rate fallacy is a common error in logical reasoning. It seems natural to conclude that if A is associated with B, then B must be associated with A. Statistically, that is true, but if A is extremely rare, then the likelihood of B given A can be considerably less than the likelihood of A given B.

So I don't think therefore that we need to seek explanations for the apparent inconsistency that's being flagged up on Twitter between rates of incarceration in studies of those with DLD, vs rates of DLD in those who are incarcerated. It could just be the consequence of the low base rate of incarceration.

References
Anderson et al (2016) Language impairments among youth offenders: A systematic review. Children and Youth Services Review, 65, 195-203.

Norbury, C. F.,  et al. (2016). The impact of nonverbal ability on prevalence and clinical presentation of language disorder: evidence from a population study. Journal of Child Psychology and Psychiatry, 57, 1247-1257.

*An R script for generating this figure can be found here.


Postscript - 4th November 2017
The Twitter discussion has continued and drawn attention to further sources of information on rates of language and related problems in prison populations. Happy to add these here if people can send sources:

Talbot, J. (2008). No One Knows: Report and Final Recommendations. Report by Prison Reform Trust. 

House of Commons Justice Committee (2016) The Treatment of Young Adults in the Criminal Justice System.  Report HC 169.

The allure of autism for researchers

Data on $K spend on neurodevelopmental disorder research by NIH: from Bishop, D. V. M. (2010). Which neurodevelopmental disorders get researched and why? PLOS One, 5(11), e15112. doi: 10.1371/journal.pone.0015112

Every year I hear from students interested in doing postgraduate study with me at Oxford. Most of them express a strong research interest in autism spectrum disorder (ASD). At one level, this is not surprising: if you want to work on autism and you look at the University website, you will find me as one of the people listed as affiliated with the Oxford Autism Research Centre. But if you look at my publication list, you find that autism research is a rather minor part of what I do: 13% of my papers have autism as a keyword, and only 6% have autism or ASD in the title. And where I have published on autism, it is usually in the context of comparing language in ASD with developmental language disorder (DLD, aka specific language impairment, SLI). And, indeed in the publication referenced in the graph above, I concluded that there was disproportionate amounts of research, and research funding, going to ASD relative to other neurodevelopmental disorders.

Now, I don’t want to knock autism research. ASD is an intriguing condition which can have major effects on the lives of affected individuals and their families. It was great to see the recent publication of a study by Jonathan Green and his colleagues showing that a parent-based treatment with autistic toddlers could produce long-lasting reduction in severity of symptoms. Conducting a rigorous study of this size is hugely difficult to do and only possible with substantial research funding.

But I do wonder why there is such a skew in interest towards autism, when many children have other developmental disorders that have long-term impacts. Where are all the enthusiastic young researchers who want to work on developmental language disorders? Why is it that children with general learning disabilities (intellectual retardation) are so often excluded from research, or relegated to be a control group against which ASD is assessed?

Together with colleagues Becky Clark, Gina Conti-Ramsden, Maggie Snowling, and Courtenay Norbury, I started the RALLI campaign in 2012 to raise awareness of children’s language impairments, mainly focused on a YouTube channel where we post videos providing brief summaries of key information, with links to more detailed evidence. This year we also completed a study that brought together a multidisciplinary, multinational panel of experts with the goal of producing consensus statements on criteria and terminology for children’s language disorders – leading to one published paper and another currently in preprint stage. We hope that increased consistency in how we define and refer to developmental language disorders will lead to improved recognition.

We still have a long way to go in raising awareness. I doubt we will ever achieve a level of interest to parallel that of autism. And I suspect this is because autism fascinates because it does not appear just to involve cognitive deficits, but rather a qualitatively different way of thinking and interacting with the world. But I would urge those considering pursuing research in this field to think more broadly and recognise that there are many fascinating conditions about which we still know very little. Finding ways to understand and eventually ameliorate language problems or learning disabilities could help a huge number of children and we need more of our brightest and best students to recognise this potential.