This PhD project assesses the predictive validity of the newly adapted UK-CDI questionnaire (see Chapter 2.3., Alcock et al., in prep) between 12 and 36 months. This PhD is a longitudinal project which includes typically developing children from a range of socio-economic backgrounds from the East Midlands (UK) with no known clinical or developmental disorders. It is essential to have appropriate assessment methods with long-term reliability to identify children at risk of language delay early in life. However, the most commonly employed UK language assessments for young children have so far not yet been assessed for their predictive validity. For example, the Ages and Stages Questionnaire (ASQ, see Squires, Twombley, & Bricker, 2009) is currently in use as a population-based screening tool for children between 24 and 30 months to detect developmental delay. This parent-report questionnaire examines all areas of development but includes very few questions about communication and language. As yet, the ASQ does not provide UK norms and no predictive validity data for British children (Bedford, Walton, & Ahn, 2013; Velikonja et al., 2016).
Standardised tests are a different tool available for UK infants and commonly used by Speech and Language Therapists if a child has been referred to them due to slow or atypical language development. The gold standard for British English assessments are the UK Preschool Language Scales (Zimmerman et al., 2014) for language and the Bayley Scales of Infant and Toddler Development (Bayley, 2010) for cognitive, motor and language skills. While these tests have been standardised, they afford lengthy and time-intensive in-person testing with the child and, again, have not been assessed for their predictive validity by the test developers.
While we cannot assume good predictive validity for the UK-CDI from the findings of other CDIs, other research methods have also found good predictability during early communication development. For example, observational research during parent and child interactions (e.g., Iverson & Goldin-Meadow, 2005; Rowe et al., 2008) ascertained that gestures were associated with later vocabulary comprehension and production; a pattern which was also found in the above mentioned CDI studies (Bavin et al., 2008; Feldman et al., 2000; Kreisman, 2012; P. Lyytinen et al.,
119 1996; Sachse et al., 2007) with few exceptions (Fish & Pinkerman, 2003; Rose et al., 2009). This supports the view that some prediction is possible but we still require an instrument which can be used for this purpose.
The UK-CDI was the tool of choice for this project as it has been standardised and it is a normed parent-report language and communication questionnaire (Alcock et al., 2017). It can be especially valuable for researchers and clinicians alike due to its cost-effectiveness and ease of administration and measurements. It is also the first standardised CDI for British-English speaking children and it is based on a representative sample of children across the UK’s regions and population, including data representative for gender and ethnic background. This newly developed parent-report instrument is for children between 8-18 months and focuses on communication, in particular on receptive and expressive vocabulary and gestures. While the psychometric properties of the newly standardised UK-CDI have been examined for internal consistency, reliability and validity as described above (see Chapter 2.3.), there is no data about how well we can predict children’s later language outcomes from early UK-CDI scores. Such data would be important and useful for early years practitioners and clinicians for use in daily practice, and for researchers to use in empirical studies on children’s language acquisition and language delay. Whilst the predictive validity of other versions of CDIs:WG have been assessed (see previous chapter) and good predictability could be generally shown during the early years, we cannot automatically assume that the UK-CDI yields the same results. This is because direct comparison between cultures may be problematic, for example, as parental interaction styles across cultures may differ (e.g., Greenfield, Keller, Fuligni, & Maynard, 2003; Weber, Fernald, & Diop, 2017) or language-specific differences may lead to different rates of language development (Bleses, Vach et al., 2008; Bleses, Basboll, Lum, & Vach, 2011). For example, Hamilton et al. (2000) found that differences exist between US American children’s language learning and the Oxford-based samples of British children with American children showing higher CDI scores.
120 For British English, attempts to investigate predictability from non-normed data sets using the Oxford CDI (Hamilton et al., 2000) have been made, mostly to study late talkers and their later language abilities, but also to predict children’s school-age language and literacy from infant vocabulary (Duff, Nation, Plunkett, & Bishop, 2015; Duff, Reen, Plunkett, & Nation, 2015; Cochet & Byrne, 2016). Results suggest that there is a strong relationship between early vocabulary comprehension and later vocabulary comprehension and production as well as between early production and later production between 1 and 3 years (Cochet & Byrne, 2016). However, children classified as late talkers in terms of expressive vocabulary at 18 months fell within the normal range and did not differ any more from typical children at 7 years in terms of language and literacy skills, although, classification (SLI versus typical children) at 4 years showed good stability when tested again at 7 years (Duff et al., 2015). Whilst it was not possible to predict language outcomes on an individual level, group level analysis showed that infant vocabulary (16-24 months) significantly predicted later vocabulary for children aged between 4 and 9 years. When taking family risk for language and literacy difficulties into account, the prediction was even better particularly for reading outcomes (i.e. infant vocabulary explained 30% of variance in later reading comprehension) as children with a family risk and small vocabularies were more likely to develop reading problems (Duff, Reen et al., 2015). However, the data was gathered using the Oxford CDI which is described as a translation of the MB-CDI. It leaves out the gesture scale and in one instance has been used for a different age range than advised. Furthermore, it has not been standardised and it has no valid UK-wide norms.
The newly standardised UK-CDI offers the chance to overcome these problems. The UK-CDI in combination with other tools enables us to investigate the predictability of gesture, comprehension and production in typically-developing children and compare children’s results to valid population norms.
If the UK-CDI has good predictive validity up to 2 or 3 years, children with language delay could be identified earlier. It is possible that the standardised UK-CDI could be used as a population-based
121 tool to determine language status, similar to the German FRAKIS (Szagun, Stumper, & Schramm, 2009). Currently, no other detailed and at the same time cost-effective and easy to administer tool for determining language status exists. So far, the UK-CDIs predictive validity has not yet been assessed. Hence, this PhD project plans to close this gap in the literature.
The aims of the current study are as follows. The UK-CDI’s short-term (12 - 18 months; 18 - 24 months) and long-term (12 - 24 months; 12 - 36 months; 18 - 36 months) predictive validity will be examined for the first time. This PhD research reports the predictive validity of the UK-CDI using a UK sample of typically developing children. It was beyond the scope of this longitudinal research to follow the trajectories for children at-risk for language problems, hence we limited ourselves to a neurotypical sample.
Predictive validity will be assessed in terms of language level. It will be examined if four groups of children (i.e. low (1-25th percentile), low-medium (26th-49th), medium-high (50th-74th) and high
level (75th-99th)) remain stable over time or whether predictions are better for some groups than
for others. This corresponds with the study by Duff et al. (2015) who also used the 25th percentile
as the cut-off for the late-talking group at 18 months.
Research has shown that language scores of early talkers between 13 and 20 months as well as early and late talkers between 20 and 26 months were stable; however, the stability of language was somewhat stronger for early talkers (Thal et al., 1997). The current study will extend the study by Thal et al. (1997) by assessing different age groups (12, 18, 24 and 36 months).
There are several CDI: Words and Gestures studies which predicted language up to 36 months or even later (see previous chapter). At this stage most children are confident users of a large vocabulary and utter sentences of increasing grammatical complexity. Therefore, many studies use standardised language measures at the follow-up stage. These usually measure receptive and expressive language but do not give an indication of vocabulary ability alone. The current study used CDI-type questionnaires at all age points (12, 18, 24 and 36 months) as a measure of vocabulary (amongst other categories) which allows the direct comparison of vocabulary over time.
122 In addition, CDIs measure additional age-appropriate skills (e.g. gestures during infancy, grammar during toddlerhood). Therefore, it will also be possible to establish if later acquired skills using further assessment tools (i.e. CDIs, PLS-5 UK and ASQ-3) can be predicted from early communicative skills recorded on the UK-CDI.
Apart from language skills, the current study also measures the effects of other factors. In contrast to most other CDI predictive validity studies, this study includes background information about the child and family (e.g. socio-economic data, child’s health status). The current study also includes other areas of development and more detailed child and family characteristics using the UK-CDI Family Questionnaire (e.g. prematurity, gender, SES, sibling status, ear infections, sleep, family risk of dyslexia or speech or language problems) to aim for a more holistic representation of child development over time and factors influencing children’s language outcomes.
As cognitive processing (e.g., Rose et al., 2009) and motor development (e.g., Iverson, 2010; Leonard & Hill, 2014) are associated with language development, these skills were measured as well to assess how early language and other factors influencing language development help to predict outcomes at 2 and 3 years. Taking into account these different factors, this will show if language development differs depending on subgroups (Reese & Read, 2000).
As the UK-CDI is a new instrument which may have effective practical use, it is important to evaluate its classification accuracy. It will be examined which children with low UK-CDI scores at 12 or 18 months will go on to have delayed language at 24 or 36 months.
Based on the review of the previous studies using CDIs surveyed in Section 3, the predictive outcomes of the UK-CDI are likely to be the following:
1) We expect stronger associations if the same linguistic domain is tested at follow-up (e.g. production scores to correlate with production scores at the next stage).
2) We also assume stronger associations with another CDI measure at follow-up compared to a different instrument used at the same age (for example CDI:WS versus PLS-5 UK)
123 3) We expect stronger associations between UK-CDI:WG and later scores if the time interval is shorter (for example: stronger correlations between 12 and 18 months compared to 12 and 36 months)
4) Furthermore, as language is more established at 18 months compared to 12 months, we assume stronger correlations of UK-CDI:WG scores at 18 months with later language skills. 5) We expect that the language of high ability children as classified on the UK-CDI:WG to
remain more stable over time compared to those children with low language ability
6) The individual prediction for later language status is expected to be difficult but may be improved with modified criteria. In this study, it will be assessed if predictions for later language delay (at 24 or 36 months) can be improved by using higher cut-off scores of early delay (at 12 or 18 months) than commonly employed by researchers.
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