Box 2.

—Clinical criteria

• General language group—a standardised score <1.2 SD (standard deviation) below the mean on the auditory comprehension part of the preschool language scale¹¹
• Expressive language group—a standardised score >1.2 SD below the mean on auditory comprehension but <1.2 SD below the mean on the expressive language part of the preschool language scale
• Phonology group—auditory comprehension and expressive language scores >1.2 SD below the mean but with an error rate of at least 40% in the production of fricative consonants (for example, f and s) and/or velar consonants (for example, “hard” c, “hard” g, and ng) and/or sounds occurring after a vowel among the 22 words included in the phonological analysis