Prevalence Estimates in the Field of Speech and Language Disorders

Prevalence estimates in the field of speech and language disorders are difficult. One reason for this is

A) researchers often disagree on the definition and classification of speech and language delays and disorders.
B) children in other categories of exceptionality rarely show speech delays but they often have language disorders which muddy prevalence figures.
C) many terms are used to describe language delays and disorders although terminology in the area of speech disorders is fairly clear- cut.
D) health statistics are unreliable.
E) although we can clearly define the different types of speech disorders, language disorders remain controversial and ambiguous.