Introduction

Children's productions of target consonants have been the focus of research for a few decades. There are two main reasons why consonants have been studied more than vowels: (1) errors in vowels are more scarce; and (2) the pronunciation of vowels is generally more sensitive than that of consonants to dialectal differences. The proportion of consonants correct (PCC) (e.g. Shriberg et al., 1997) has been widely used in the literature since the mid-1980s and also in practice for assessing children's consonants in typical and atypical language development. It was not until the early 2000s that a phonological measure was proposed to evaluate whole-word productions. Ingram and Ingram (2001) and Ingram (2002) introduced the phonological mean length of utterance (PMLU) as the arithmetic mean of the PMLU of individual words, which is defined as the sum of the produced vowels and the substituted consonants plus twice the correctly produced consonants. The same authors introduced the proportion of word proximity per word, referred to as phonological word proximity (PWP), as the proportion of the produced PMLU to the target PMLU, with the PWP for a number of words in a speech sample being the arithmetic average of the PWP of individual words.

Several researchers have applied PMLU and PWP to evaluate speech performance in monolingual and bilingual child speech. Taelman et al. (2005) discussed how to use CLAN (MacWhinney, 2000) to compute PMLU and PWP using large sets of speech data. Bunta et al. (2009) compared three-year old Spanish-English bilingual children to their monolingual peers to compute, among other quantities, PWP and PCC. They found that while PWP and PCC differ in general, bilinguals only differ on PCC from their monolingual peers in Spanish and that when comparing the Spanish and English of the bilingual participants, PCC was significantly different but PWP was similar. Burrows and Goldstein (2010) compared PWP and PCC accuracy in Spanish-English bilinguals with speech sound disorders (SSDs) to age-matched monolingual peers.