Category: child language

The Ecological Fallacy – When to Intervene?

I’ve been doing a bit of reading to prepare for my next placement in paediatric community health.
In an intriguing paper, Ukoumunne and colleagues pushed the ELVS data through a statistical machine to discern discrete trajectories of language impairment and precocity. The best fit had five average paths for the children’s language between 1 and 4 years:

  • Typical: 68.5% of children stayed pretty average
  • Precocious (late): These children started typical, but were more likely to outpace their peers from 24 months.
  • Impaired (early): These children were impaired up to 12 months, but were typical by 2-4 years.
  • Impaired (late): Typical development to 2 years, with impairment from then to 4 years.
  • Precocious (early): Likely precocity early on with a return to typicality at 4 years.

The authors are keen to stress that these paths are averages, and do not predict what individual children might achieve. To apply this analysis in a clinical context would be to commit the Ecological Fallacy, “where inferences about the nature of individuals are deduced from inference for the group to which those individuals belong“.

An example

Suppose there is a suburb called “Exampletown” with 400 residents who each earn $60,000/annum, except for one who earns $50 million/annum (an extreme example, but good for making the point!). The average income for Exampletown is $184,850/annum (the median is obviously $60,000). You might read a list of suburbs ranked by average income. Say you meet someone from Exampletown – you might assume they are quite wealthy, because you know their suburb has an extremely high average income. But they aren’t! You have committed the ecological fallacy, trying to apply an inference that applies to a group to an individual member from that group.

Application to Language Delay

While the model above is seductive, it is also true that 6% of the typical group will be impaired at 4 years, and that 52% of the Impaired (late) are typical at 4 years. Because there are a lot of more in the typical group, this 6% actually represents 55% of the total number of impaired children at age 4.

People might say that the data shows that children are too variable to allow clinicians to make the call to intervene before 4 years. After all, they might improve! Or we could be taking away resources from children who will need them when their impairment manifests. It’s a tricky problem.

I have a small issue with people using the ELVS data to make clinical decisions (if they do). The study was not conducted to look at the efficacy or efficiency or early language intervention. Instead, it was an observational study: it cannot answer these questions.

It’s a rather unsatisfying conclusion, but I’ll be interested to report on what my next clinic does. All community health services suffer from chronic under-resourcing, so decisions need to be made about priorities. Are these decisions being made with reference to efficiency/efficacy data, or observational/epidemiological data?


Ukoumunne, O. C., Wake, M., Carlin, J., Bavin, E. L., Lum, J., Skeat, J., . . . Reilly, S. (2012). Profiles of language development in pre-school children: A longitudinal latent class analysis of data from the Early Language in Victoria Study. Child: Care, Health and Development, 38(3), 341-349. doi: 10.1111/j.1365-2214.2011.01234.x


How does language develop in bilingual children?

This is an old assignment that I thought might be a good place to start for the blog. Excuse the bright, chirpy, parent-friendly tone.

The 2011 Australian Census revealed that 15% of children under 5 are growing up in bilingually (ABS, 2011). This means they either speak two languages at home, or one language at home and another outside of the home. Monolinguals, by contrast, speak only one language in all environments. Their exposure to each language may vary from hearing mostly English with just a little bit of their home language to hearing only their home language with the only English coming from outside the home. Most of these children would be simultaneous bilinguals meaning they are learning both languages at once. This is different from successive bilinguals who become fluent in one language before they begin another (like a child born to Italian migrants who only begins learning English in her first year of school).

"A dog by any other name would smell."

“A dog by any other name would still bark.”

What do we mean by language? A language is a system that allows communication between people. Messages are sent, received and understood. This system has shared symbols: the word dog has little to do with the animal itself, but English speakers share the use of this symbol (the word) to communicate the meaning of a pet that barks, etcSpeech is a tool to use language. Speech is the physical way humans produce sound that can be understood as language by other people.

Children are not born with language. In the early years of life they learn to tell sounds apart from each other and produce them in meaningful ways. These language milestones arrive in an expected sequence following a set timeline. For example, a child’s first word normally appears at 12 months. The language a child speaks obviously depends on its environment. In bilingual homes, children are exposed to two systems at the same time. Some people believe this confuses the child, as they cannot distinguish the two languages, and end up mixing them together.

the table or la mesa?

the table or der Tisch?

We know that this is not the case. A study looked at bilingual German/English children aged two, and found that they used words in both that meant the same thing, and would say the right one given the context (Junker, 2002). This suggests that they understand that there are two ways of talking, and that they could code-switch between the languages in appropriate situations. It is also clear that the sum of their two vocabularies is equal to or greater than their monolingual peers, indicating they are learning at a faster rate, even if they seem behind in one language (Pearson, 1993; Schaerlaekens, 1995).

Language is more than just having names for objects. Children need to learn the words and endings that help put sentences together (I’ve put them in bold). An Australian study has shown that while bilingual children learn these markers more slowly than monolinguals, their rate of learning is still within the normal range for monolinguals (Nicholls, Eadie, & Reilly, 2011). When children start school they learn to become literate in their language (reading and writing). A study of bilingual children undergoing instruction in Wales revealed that the bilingual children developed literacy in Welsh within normal expectations, if slightly slower than those learning to read and write in English (Rhys, 2013).

Won’t speaking two languages to a child confuse them? Will they mix them up?

As those who have attempted or succeeded in learning a second language can attest, the process is difficult! Every language has a different vocabulary (individual words used to name things or relate things together) and a different grammar (the rules for combining words into meaningful sentences). It might seem reasonable to suggest that children hearing two languages will be confused, as they will not have developed the capacity to understand that there are different languages with different vocabularies and grammars. Parents worry that they might confuse the languages, as they have no direct cues to distinguish them.

Schaerlaekens (1995) found that children who grew up in bilingual French/Dutch environments knew when to speak each of the languages. If they were asked in French to name an object and they did not know the word in French but they did in Dutch, they would choose not to answer rather than respond in Dutch. This suggests that children are not confused by exposure to two languages, and that they develop the ability to distinguish their production and reception of them from an early age. A weakness of this study was that only fifty children out of the sample of 745 were actually assessed at multiple time-points.

Interestingly, a study by Junker (2002) showed that preschool aged simultaneously bilingual children always produce some translational equivalents (e.g. a German/English bilingual child could name a table a “table” when asked in English and a “Tafel” when asked in German). It should be noted that direct equivalents (e.g. English hand and German Hand) caused confusion. This suggests that their brains are able to develop a system for each language individually, instead of combining them into the same system.

How much of each language do they need to hear?

No child grows up in a bilingual environment where they have equal exposure to each language. A child who speaks Spanish at home in Miami, Florida will hear English in different contexts, environments and qualities from a child who attends an English immersion preschool in Madrid. Pearson (1997) found that, in general, the size of a child’s vocabulary in a given language is proportional to the amount they are exposed to. However, if the language is a minority in their community (like Tamil in Singapore for instance) and they are only exposed to low amounts of this language, there is the possibility that they will develop little to no proficiency in it. Pearson tentatively recommends that a child needs to receive at least 20% of their input in a language in order for them to develop proficiency in it, but this is not related to any of her results, and is fundamentally a guess.

Do bilingual children develop language slower?

Only if you only assess them in a single language! Pearson (1993), Schaerlaekens (1995) and Hoff (2012) all found that while simultaneously bilingual children may score lower on vocabulary measures when measured on one language only, if the figures for both languages are combined (and translational equivalents removed), the figures equal or exceed their monolingual peers. Nicholls, Eadie, & Reilly (2011) found that bilinguals children aged three had generally acquired fewer grammatical markers (e.g. I was going to clean the shower), but that they acquired them in the same order as their monolingual peers. Schaerlaekens (1995) found that, from the age of four, there was no difference between the bilingual’s and monolingual’s vocabulary measures in single languages. There have been no large scale studies to date that tracked bilingual children’s language development from preschool through to adolescence.

Are bilingual children at greater risk of Language Impairment?

No research has shown Language Impairment (LI) to be aggravated by bilingualism, and Paradis (2010) recommends dual language environments for bilingual children with LI if they are easily created. In a study of Finnish/Swedish bilingual children in Sweden, Westman (2008) identified those at risk for LI at age five and reassessed them a year later. They found that bilingual children with LI had similar profiles to a control group of monolingual children with LI, suggesting that bilingualism does not aggravate LI. They did note an increased risk of LI in the bilingual group, but this was believed to be a result of language testing in Swedish only (as the children’s Finnish was not assessed).

If they only hear the language from me, does that matter?

Yes. While monolingual children may be mostly fluent in their language before they go to school, at school they develop this language in sophisticated ways, learning how to read and write in it, how to express complex ideas in a variety of contexts, and how to build social connections using it.

Rhys (2013) looked at the vocabularies and reading abilities of children attending Welsh immersion schools, and found that majority (English) speakers faced no detriment to their home language by being instructed in Welsh only. On the other hand, Welsh speakers required the immersion schooling in order to develop their language, as the broader social environment did not facilitate their acquisition (as English is dominant). To develop bilingual competency, children need to be exposed to a variety of environments in each language.

Is the one-parent-one-language method the best/only way?

An example of this method would be when a mother only speaks to her children in French and the father only in Arabic, in all environments. In general, the evidence suggests that children are capable of distinguishing languages from an early age, and will not become confused in hearing an adult speaking both languages. There is no clear evidence relating the success of children learning two languages in a fluctuating linguistic environment. For example, Pearson (1997) reports no correlations between linguistic abilities and any other factors in children who were exposed to changing amounts of Spanish and English.

So it’s alright to raise my child bilingually?

There is no strong evidence indicating that children should not be raised bilingually; however, the research described above has some serious flaws. Firstly, sample sizes were often small, and most only followed the children over a period of months, making it difficult to assess long-term outcomes. Also this means that the researchers have extrapolated to make their conclusions – they have not observed bilingual children acquiring language from birth to adolescence. Secondly, many only used published norms as a control group, making it difficult to compare the bilingual group with monolinguals.

Australian Bureau of Statistics. (2011). Table Builder: 2011 Census – Cultural and Language Diversity. Retrieved from

Hoff, E., Core, C., Place, S., Rumiche, R., Señor, M., & Parra, M. (2012). Dual language exposure and early bilingual development. Journal of Child Language, 39, 1-27. doi:10.1017/S0305000910000759

Junker, D. A., & Stockman, I. J. (2002). Expressive vocabulary of German-English bilingual toddlers. American Journal of Speech-Language Pathology, 11, 381-394.

Nicholls, R. J., Eadie, P. A., Reilly, S. (2011). Monolingual versus multilingual acquisition of English morphology: what can we expect at age 3? International Journal of Language and Communication Disorders, 46, 449-463. doi:10.1111/j.1460-6984.2011.00006.x

Paradis, J. (2010). The interface between bilingual development and specific language impairment. Applied Psycholinguistics, 31, 227-252. doi:10.1017/S0142716409990373

Pearson, B. Z., Fernández, S. C., & Oller, D. K. (1993). Lexical development in bilingual infants and toddlers: Comparison to monolingual norms. Language Learning, 43, 93-120. doi:10.1111/j.1467-1770.1993.tb00174.x

Pearson, B. Z., Fernández, S. C., Lewedeg, V., & Oller, D. K. (1997). The relation of input factors to lexical learning by bilingual infants. Applied Psycholinguistics, 18, 41-58. doi:10.1017/S0142716400009863

Rhys, M., & Thomas, E. M. (2013). Bilingual Welsh-English children’s acquisition of vocabulary and reading: implications for bilingual education. International Journal of Bilingual Education and Bilingualism, 16, 633-656. doi:10.1080/13670050.2012.706248

Schaerlaekens, A., Zink, I., & Verheyden, L. (1995). Comparative vocabulary development in kindergarten classes with a mixed population of monolinguals, simultaneous and successive bilinguals. Journal of Multilingual and Multicultural Development, 16, 477-495. doi:10.1080/01434632.1995.9994619

Westman, M., Korkman, M., Mickos, A., & Byring, R. (2008). Language profiles of monolingual and bilingual Finnish preschool children at risk for language impairment. International Journal of Language and Communication Disorders, 43, 699-711. doi:10.1080/13682820701839200