Dyslexia: An Operational Definition

Dyslexia: An Operational Definition

G. Emerson Dickman, J.D.


Three years ago at the National Orton Dyslexia Society conference in Washington DC (November 1991) one could not help but be struck by the fact that virtually every speaker (4 days, over 100 sessions) discussed their area of interest in light of their own unique definition of, “dyslexia”. The lack of a universally recognized definition clearly undermines the potential of research intended to evaluate the efficacy of methodology employed for intervention and remediation. As a consequence of the resulting research inconsistency, the Society has been assailed as a “fringe”, “special interest,” or “elitist” organization. Individual advocacy, in terms of obtaining a free appropriate public education, and group advocacy, in terms of legislative initiatives, are undermined by the inability to describe with precision the person or population intended.


Early in 1992, the New Jersey Branch commenced a project to develop a legislative initiative to recognize and respond to the needs of a dyslexic pupil. Finding no universally accepted definition, the effort turned to developing a description of characteristics that would define the population we intended to serve with sufficient precision to allow for a focused legislative response. After much discussion, it was felt that a definition should be broad enough to satisfy the legitimate interests of various professionals across disciplines yet narrow enough to direct efficacious remediation. The goal was to develop a definition that would be capable of facilitating communications and standardizing the assumptions upon which research is based and interpreted.


Scholarly journals are replete with pleas to address the issue of definition and subtyping learning disabilities. The following are three authoritative examples of a common thought which has been repeated with an increasing sense of urgency over the past decade:

“Definition is central to every facet of the process identification and provision of service for children with learning disabilities. Clearly, research results describing clinical characteristics, etiology, course, and subsequently, management of learning disabilities will depend on the criteria we choose to define learning disabilities. In addition, given the significant social and political ramifications of a particular definition of learning disability (Senf, 1986), it is not surprising that definition issues represent one of the most intensely debated topics in the field.” (Shaywitz et al, J.L.D. 12/92)

“Identification of specific syndromes may lead to more appropriate educational interventions…one wonders if the real progress will not come from disentangling groups of children from this huge conglomerate mass…” (Mather, in press)

“we must establish precise definitions … robust enough to recognize the distinctions and interrelationships (Comorbidities)…

* * *

It is obvious the to this date the field lacks logically consistent, easily operationalized and empirically valid definitions … to enhance communications or improve predictions – the two primary reasons for developing definitions …

The article also suggests that in order to validate “research practice” and the “LD construct” definitions should hav

“… logical consistency, communicative power and predicative capability.” (Lyon et al, J.L.D. 5/93)


Before attempting to build anything, it is necessary to have a fundamental understanding of the architectural principles involved. In the case of definition building, such architectural principles involve an understanding of the relationship of constructs and variables

construct is an abstraction, a theoretical concept. The theoretical concept we wish to recognize is “Dyslexia”, a learning disability that negatively impacts the ability to read. This is, of course, an oversimplification. To be more precise about what is meant by the construct of Dyslexia, we must address specific variables.

Although a single construct, Dyslexia has many different variables, each of which only partially represent the overall concept. For instance, the construct of Dyslexia is a learning disability said to be a language-based disorder thus it is not a learning disability that is not language-based; it involves insufficient phonological processing, this ruling out reading problems not involving phonological processing; and it is unexpected since it exists in the presence of relative strengths and is unexpected, thus not do to generalized developmental disability or sensory impairment. The object is to develop a matrix of variables, which are measurable, to determine if a person has “dyslexia”.

Many variables are “measurable” by simply determining whether or not they exist. Is what we are investigating language-based – yes or no? Does it involve insufficient phonological processing – yes or no? Is it unexpected – yes or no? An operational definition specifies the variables required for a researcher or diagnostician to obtain the measurements necessary to determine the existence of the construct.

In this example we have used a matrix of measurable variables to identify that portion of the population we wish to identify, at this particular time, as dyslexic.


The New Jersey Branch gathered twenty of the most prominent definitions in use at the time (early 1992). Among such definitions were the “ODS working Definition” (12/12/89) and those contained in the legislative initiatives of California, Louisiana and Texas. Each definition was analyzed and broken down into constituent elements that appeared to fall into three main categories: origin, characteristics, and exclusionary criteria. Allowing for some overlap and duplication, the elements of the definitions researched broke down as follows:


  1. Developmental language disorder
  2. Present at birth
  3. Often runs in family
  4. May be caused by naturally occurring brain differences
  5. A Neurological disorder
  6. Strong hereditary basis
  7. Appears to be related to impaired function of the brain
    centers involving language.
  8. Fundamental cognitive disabilities of constitutional disorder
  9. Disorder of constitutional origin
  10. Cognitive in essence
  11. Usually genetically determined
  12. A disturbance of cognitive functions
  13. A neuropsychological basis
  14. May be caused by deficiencies of the left hemisphere of the brain.


  1. A specific deficit in the processing of phonological information
  2. Persists into adulthood
  3. Difficulty reading
  4. Difficulty writing
  5. Difficulty spelling
  6. Characterized by inadequate acquisition of written language skills, especially reading, writing and spelling
  7. Personal and/or family history of left-handedness or ambidexterity is frequent.
  8. Erratic spelling
  9. Lack of facility in manipulating written as opposed to spoken words.
  10. Difficulty with the symbols of written language
  11. Language processing disorder which may be manifested by difficulty processing expressive or receptive oral or written language
  12. Difficulty dealing with abstract symbols of written language
  13. Affects a range of information processing skills
  14. Limits the ability to perform written language tasks – reading, writing and spelling
  15. Difficulty with language
  16. Persistent difficulty with language manifested in an inability to learn to read, write, spell, speak, or listen
  17. An invisible handicap
  18. An inefficiency or impairment in processing language that is heard, spoken and/or written.



  1. Average to above average intelligence
  2. Adequate intelligence
  3. Not due to intellectual inadequacy
  4. Normal intelligence
  5. Ability to learn not commensurate intellectual potential
  6. At least average intelligence


  1. Difficulty learning to read despite conventional instruction
  2. Difficulty learning to read despite socio-cultural opportunity
  3. Difficulty not due to false technique of teaching
  4. Difficulty not due to emotional factor
  5. Despite adequate educational exposure
  6. Despite adequate cultural opportunity
  7. Despite appropriate desire to achieve
  8. Despite normal hearing and vision

Each element in each category was examined from the perspective of Dr. Lyon’s prerequisites, i.e., “logical consistency,” “communicative power,” and “predictive capability.” The result was the first draft with seven pages of rationale that was submitted to selected reviewers by the NJODS in January 1993. Within the following months the list of official reviewers expanded significantly.

By November 1993, in time for the National Conference in New Orleans, the 12thdraft was ready to present to the National Board.

Whoa! You’re going too fast:

Shortly before the conference, after almost two years of steady progress with virtually no voiced decent, a faction developed expressing an emotional and global opposition to the proposed definition. Although, at the time, there appeared to be little potential for meaningful debate, the unexpected vehemence of the opposition caused us to critically reflect on the merits of the product and to seek out a higher-level professional input, theretofore only tangentially involved.


On April 9-10, 1994, a consensus meeting, was held at the Hyatt Hotel in New York City. This meeting brought together Bill Ellis, ex-president of ODS and professional director of the National Center for Learning Disabilities in NYC; Jack Fletcher, Ph.D., Professor of Pediatrics at the University of Texas; Bennett Shaywitz, M.D., Professor of Pediatrics, Neurology and Child Study at Yale University School of Medicine; Sally Shaywitz, M.D., Professor of Pediatrics and Child Study at Yale University – School of Medicine; Reid Lyon, Ph.D., from the Human Learning and Behavior Branch National Institute of Child Health and Human Development, Bethesda, M.D.; Bruce Pennington, Ph.D., Professor of psychology at University of Denver; and Byron Rourke, Ph.D., Professor of psychology at University of Windsor, Windsor, Ontario.


Dyslexia is one of several distinct learning disabilities. It is a specific language-based disorder of constitutional origin characterized by difficulties in single word decoding, usually reflecting insufficient phonological processing abilities. These difficulties in single word decoding are often unexpected in relation to age and other cognitive and academic abilities; they are not the result of generalized developmental delay or sensory impairment. Dyslexia is manifest by variable difficulty with different forms of language, often including, in addition to problems reading, a conspicuous problem with acquiring proficiency in writing and spelling.


The definition can be broken into six sections:


Dyslexia is one of several distinct learning disabilities

“We use the term learning disability in a generic sense to include all types of learning disability. Reading disability or dyslexia represents a particular type of learning disability in which reading is primarily affected. Though dyslexia is the most frequently observed learning disability, other learning disabilities may reflect arithmetic (dyscalculia), handwriting (dysgraphia), or spelling disabilities.” (Shaywitz et al 1994)

As simple and obvious a concept as subtyping learning disabilities may be, we still live in an educational environment where generic remedial methodology is used to address the needs of the student generically diagnosed as learning disabled. The nonverbal learning disabled child with weaknesses in visuospatial and tactile-kinesthetic processing is treated the same as a dyslexic whose primary weakness is in the processing of auditory information.

“[D]isentangling groups of children from this huge conglomerate mass” (Mather, in press) is indeed a significant goal, as yet unrealized.


It is a specific language-based disorder

Dyslexia is identified initially in terms of its functional impact, rather than identifying a particular area of weakness. The word “specific” is used to indicate that Dyslexia is only one of various possible language-based disorders.

of constitutional origin

According to the definition in Webster’s, “constitutional” means “belonging to, or inherent in, the structure of body or mind;…”

characterized by difficulty in single word decoding, usually reflecting insufficient phonological processing abilities.

“Central to and most prominent in this definition is the recognition that dyslexia represents a disorder of language, and even more specifically, difficulties with a particular component of the language system – phonological processing, a problem that is manifest by difficulties in decoding words. ” (Shaywitz et al 1994)

In his discussion of dyslexia, Bruce Pennington (Diagnosing Learning Disorders) states in part:

“When we read we go from letters to phonological representations, and when we spell, we go from phonological representations to letters.

* * *

… dyslexics have a higher rate of spoken language problems, . . .These spoken-language symptoms of dyslexia are easily understood if dyslexia is conceptualized as a phonological processing disorder; . . .”

In the Journal of Learning Disabilities (1993), Louisa Moats and Reid Lyon stated:

” . . . individuals with dyslexia are distinguished by their phonologically based decoding disability,. . .”

In the Annals of the New York Academy of Sciences (1993), Paula Tallal, Steve Miller, and Roslyn Holly Fitch stated:

“We suggest that these basic temporal deficits cause a cascade of effects, starting with disruption of the normal development of an otherwise effective and efficient phonological system. We propose further that these phonological processing deficits result in subsequent failure to learn to speak and to read normally. That is, both the language and reading problems have their basis in deficiently established phonological processing and decoding.”

It is clear that the most professional and well-constructed discussions of dyslexia focus on phonological processing or phonological awareness. “Reading requires good phonemic awareness; this notion appears irrefutable.” (William Ellis, 1993)


These difficulties in single word decoding are often unexpected in relation to age and other cognitive and academic abilities;

“A second critical component of the definition incorporates the concept that the difficulty in reading is ‘unexpected in relationship to … age and other cognitive and academic abilities.’ This notion of an unexplained difficulty in acquiring academic skills is basic to almost all definitions of learning disability, originating with the first use of the term learning disabilities’

* * *

This reformulation of the definition of reading disability maintains the notion that there is an unexpected difficulty’ in single word decoding but removes the necessity of establishing a ‘quantified discrepancy’ between reading achievement and ability. Thus, in the child, reading disability may be manifest by evidence of low achievement in reading together with indication of cognitive strengths in other domains, but not necessarily expressed as an ability-achievement discrepancy.

* * *

More problematic is the issue of just how to define what is meant by ‘unexpected’ in the older individual, in the adolescent or young adult.

* * *

We have likened the pattern of cognitive skills in dyslexic individuals to an encapsulated deficit (phonological processing) within a sea of strengths (e.g., concept formation, reasoning, critical thinking). Using these cognitive abilities, the older individual with dyslexia may have been able to compensate for his or her deficit in decoding and it may be very difficult to demonstrate a deficit in reading accurately.

* * *

A developmental history of difficulties with language particularly phonologically based components of language, often provides the clearest and most reliable indication of a reading disorder.

* * *

The requirement of excessive amounts of time in relation to the high level of competency achieved represents the hallmark of a reading disability in a compensated dyslexic.” (Shaywitz et al, 1994)


They are not the result of generalized developmental delay or sensory impairment.

“This new definition also incorporates only two exclusionary criteria (generalized developmental disability or sensory impairment). Specifically, children are not excluded on the basis of economic, cultural, or environmental disadvantage, a practice that lacks any empirical validation. Clearly, reading disability is more common in children coming from socially disadvantaged homes (Rutter and Madge, 1976); yet there is no evidence that the nature of the disability in disadvantaged children differs from that found in middle or upper class children (Rutter, Tazard & Whitmore, 1970). Data from the Florida Longitudinal Study (Taylor, Staz & Friel, 1979) challenges such exclusionary definitions, and suggests that disadvantaged children should not be arbitrarily excluded from a diagnosis of dyslexia.” (Shaywitz et al, 1994)


Dyslexia is manifest by variable difficulty with different forms of language,

The reference to “different forms of language” allows for the observation that dyslexics often evidence problems with the language-based demands of tasks usually considered strengths, e.g., math and science.


often including, in addition to problems in reading, a conspicuous problem with acquiring proficiency in writing and spelling.

At present, and for the foreseeable future, written language problems, decoding and encoding, are the most “conspicuous” manifestations of the dyslexic profile. Given the neurological etiology of the disorder, it must be accepted that dyslexia existed before the printed word, and will exist after written language proficiency, as we know it, becomes a vestigial art; in which case, dyslexia would lose its ranking as a disorder requiring a definition or remediation. However, the current technological status of our society enhances and spotlights the academic, social and vocational impact of the dyslexic’s difficulty in acquiring written language proficiency. It is also recognized that a dyslexic may experience problems with organization, sequencing transpositions, reversals and memory that can have significant impact on the acquisition of fundamental math skills and achievement in other content courses requiring retention of rote knowledge as compared to development of conceptual and analytic skills.


“Operational definitions are never completely adequate. They are necessary but rarely seem sufficient to capture the rich and complex ideas contained in a theoretical construct. The beauty of an operational definition is that it specifies precisely how to measure a variable in such a concrete and specific
manner that anyone else could repeat the steps and obtain the same measurements.

* * *

Scientific measurement is accomplished with operational definitions that can be used and repeated by any number of people. This factor is what makes operational definitions objective.

* * *

The emphasis on objectivity does not guarantee truth or accuracy, but it does permit scientists to communicate with one another and with the public. It also permits anyone to challenge and check a piece of research because the operational definitions are instructions for replicating an observation.

* * *

In addition, by acknowledging the imperfection of all our current measures, we leave room for improvement, without which there would be little hope for scientific advance.” (Judd et al 1991)

Clearly, the necessity for measurable objectivity in an operational definition requires the sacrifice of the totality of variables necessary to convey the “rich and complex ideas” many feel should be included.

“[C]oncrete measures will always fall short of conveying the full richness of the intended construct.” (Judd et. al., 1991)


Bruce Pennington Ph.D. University of Denver, author of “Diagnosing Learning Disabilities”

“I will use the definition in my scientific writing about dyslexia and in communicating with parents and educators.” (5/12/94)

Bennett Shaywitz, M.D. Director of Pediatric Neurology, Yale University School of Medicine:

“We think the definition is terrific and we would like to use it in several articles and chapters we are now submitting.” (5/9/94)

The Scientists at the National Institute of Child Health and Human Development (NICHD) ”approved” the definition for use and have used it in requests for proposals for Federally funded research.

Reid Lyon, Ph.D. in an upcoming text by Russell Barkley on Child Psychopathology:

“…the Orton Dyslexia Society Research Committee has constructed a new definition of dyslexia that reduces the exclusionary language inherent in all definitions of LD and dyslexia and defines dyslexia using the most current and valid research evidence available at this time.

* * *

The construction of this new definition provides a good example of how research can inform both policy and practice.” (in press)

Shaywitz, Fletcher & Shaywitz, in a recent issue of the Canadian Journal of Special Education state that dyslexia is now the “best defined of the learning disabilities.”


Two years ago potential reviewers of the proposed definition were told that “The lack of a universally recognized definition results in the Society often being assailed as a fringe, special interest or elitist organization.” This is no longer the case. The impact of a recognized definition consistently applied within and across professional disciplines means a focus and consistency in research; a diagnostic tool with empirical validity; and the ability to advocate for efficacious remediation; all heretofore absent. However, no single definition can satisfy all needs, i.e., this definition is a scientific definition meant for use primarily by researchers, funding sources, and professional diagnosticians. Other, consistent, but presumably less operational, definitions may have to be developed that have more utility with nonprofessionals and media. In the meantime, the definition of the Research Committee of the Orton Dyslexia Society may have finally opened the doors of public education to the advantages of multisensory, phonics based programming for the “most common” and now “best defined” of all learning disabilities, Dyslexia!

We are currently experiencing the confluence of four factors:

1. the subtyping of learning disabilities,

2. diagnostic criteria derived from a recognized operational definition of dyslexia,

3. disenchantment with whole language as an effective methodology for poor readers, and

4. longitudinal research strongly supporting the efficacy of a Multisensory, structured, sequential, cumulative, phonics based approach to intervention and remediation. (Torgeson et al, 1994)

The potential for the students we have fought so long to support is obvious and significant.