Sunday, January 27, 2008

Developmental Dyscalculia, Part 2

Definition, Prevalence, and Prognosis

Shalev, Auerbach, Manor, and Gross-Tsur (2000) offer two different definitions for developmental dyscalculia. First, they offer that developmental dyscalculia is a specific, genetically determined learning disability in a child with normal intelligence. The usefulness of this definition, however, is limited when it comes to differentiating students with dyscalculia and students who are simply weak in arithmetic. A more recent definition according to the DSM-IV-R is offered as well, which defines developmental dyscalculia as a learning disability in mathematics, the diagnosis of which is established when arithmetic performance is substantially below that expected for age, intelligence, and education.

Prevalence studies have been carried out in different countries, all with various different definitions for developmental dyscalculia. Despite the definitional inconsistency, the prevalence of developmental dyscalculia across countries is fairly uniform, at about 3-6% of the school population. That percentage is similar to the population with developmental dyslexia and with attention deficit/hyperactivity disorder.

The manifestation of developmental dyscalculia generally changes with age and grade. First graders (age 5-6) typically present with problems in the retrieval of basic arithmetic facts and in basic computational exercises. Older children (age 9-10) have finally mastered counting skills, are able to match written Arabic numerals to quantities of objects, understand concepts of equivalence or inequivalence (more than/less than/equal to), and understand the ordinal value of numbers. They also are generally proficient with handling money and understanding the calendar (Shalev and Gross-Tsur, 2001). Children diagnosed with developmental dyscalculia at this age present with deficits in the retrieval of overlearned information (e.g. multiplication tables) – in an attempt to bypass their difficulty in solving basic arithmetic problems, these children will use inefficient strategies in calculation. Errors typically include inattention to the mathematical operator, use of the wrong sign, forgetting to “carry over,” or misplacement of digits (Shalev and Gross-Tsur, 2001).

Longitudinal studies of dyscalculia are few and far between, so not much is known about the prognosis of those individuals who are diagnosed with developmental dyscalculia. Shalev, Auerbach, Manor, and Gross-Tsur (2000) followed a group of 140 ten and eleven year old children who had developmental dyscalculia, and reexamined them at age thirteen and fourteen. Their performance, after three years, was still poor, with 95% of the group scoring in the lowest quartile of their school class. Fifty percent continued to meet the research criteria for developmental dyscalculia. Shalev, Manor, and Gross-Tsur (2005) did a second follow-up, after six years, when the group was finishing their secondary school studies, at age sixteen and seventeen. 51% of the group could not solve 7x8 (versus 17% of controls); 71% could not solve 37x24 (versus 27%); 49% could not solve 453 (versus 15%); and 63% could not solve 5/9 + 2/9 (versus 17%). Forty percent of the group scored in the lowest fifth centile for their grade. Of those who scored above the lowest fifth, ninety-one percent still scored in the lowest quartile. Children whose diagnosis of developmental dyscalculia had persisted also presented with more behavioral and emotional problems than those with non-persistent developmental dyscalculia. These problems included anxiety/depression, somatic problems, withdrawal, aggression, and delinquent behavior. Cognitive factors associated with persistent developmental dyscalculia were lower IQ, inattention, and writing problems.

Unlike dyslexia, ADHD, and other learning disorders, which show more males than females affected, developmental dyscalculia shows a more equal distribution between the sexes. To date, no convincing answer for why the usual predominance of boys is not shown in developmental dyscalculia has been offered. Many researchers have attributed other non-neurological factors to the etiology of developmental dyscalculia, most of which may preferentially impact girls more than boys, including lower socio-economic status, mathematics-induced anxiety, overcrowded classrooms, and more mainstreaming in schools (Shalev, Auerbach, Manor, & Gross-Tsur, 2000).

References:

  1. Shalev, R.S., Auerbach, J., Manor, O., & Gross-Tsur, V. (2000). Developmental dyscalculia: prevalence and prognosis. European Child and Adolescent Psychiatry, 9(2), 58-64.
  1. Shalev, R.S., & Gross-Tsur, V. (2001). Developmental dyscalculia. Pediatric Neurology, 24, 337-342.
  1. Shalev, R.S., Manor, O., & Gross-Tsur, V. (2005). Developmental dyscalculia: a prospective six-year follow-up, Developmental Medicine and Child Neurology, 47, 121-125.

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