Tuesday January 26 2010
The study was based on a small sample of ambidextrous children
Ambidextrous children are “more likely to have mental health problems and difficulties in school”, according to The Daily Telegraph.
The news is based on a study of 8,000 children that assessed how hand dominance was linked to behaviour, language ability and school performance at eight and 16 years. This research had a number of limitations, including the fact that only 87 children were ambidextrous. Also, rates of developmental and mental health problems were based on the results of questionnaires given to the children, parents and teachers and not on professional assessments. Without formal assessments it is not possible to determine whether the children truly had conditions such as ADHD.
The researchers do not specifically suggest that mixed-handedness directly causes problems of language and behaviour, rather that differences in the brain could be related to both. The limitations to this study mean that its results should be seen as very preliminary, and therefore should not be a cause of concern for parents.
Where did the story come from?
Dr Alina Rodriguez and colleagues from Imperial College London, and other researchers from the UK, Finland and the US carried out this research. The study was funded by the Academy of Finland, Sigrid Juselius Foundation, Thule Institute, University of Oulu, and the National Institute of Mental Health in the US. The lead researcher received funding from VINNMER, a Swedish programme to support research by women. The study was published in the peer-reviewed medical journal, Pediatrics.
The Daily Telegraph, The Times, The Guardian and BBC News have covered this research. The newspapers have covered this story relatively accurately, although some incorrectly suggest that dyslexia was assessed. Some reports also suggest that hyperactivity was more common in ambidextrous children. But once the researchers had adjusted for the influence of confounding factors, there was no significant difference in the proportion of children with high hyperactivity scores alone (i.e. without inattention also being present). None of the news sources touched on the limitations of this research, although the Telegraph included quotes from the study author who stressed that “most of the mixed-handed children we followed didn’t have any of these difficulties”.
What kind of research was this?
The current study analysed data from a prospective cohort study called the Northern Finland Birth Cohort 1986. The researchers wanted to see whether there was a link between children being “mixed-handed” (ambidextrous) and their risk of having mental health issues, difficulties with language, or problems in school. Previous studies have suggested that such a link may exist in younger children. The researchers thought that if they could establish a link between ambidexterity and these problems, it might provide a way to identify children at risk of such problems.
When looking at what factors or exposures might contribute to causing a particular outcome, a prospective cohort study is usually the ideal study design to use. In this case, the researchers did not specifically believe that mixed-handedness directly causes the language or behavioural problems seen, rather that differences in the brain could contribute to both traits.
Randomly assigning participants to different groups in a study can be a way to minimise the differences between these groups, a process called ‘randomisation’. However, as a child obviously cannot be randomly assigned the dominance of a particular hand, the groups of children were not randomised and may be imbalanced for other features that could affect results. The researchers took some of these factors into account, but there may still be other factors that are having an effect.
What did the research involve?
The birth cohort study provided data on 9,479 children from the two most northerly provinces in Finland who were expected to be born between July 1 1985 and June 30 1986.
In the current analysis, the researchers assessed children’s school performance, behaviour, and whether they had any language difficulties at eight and 16 years of age. To assess these measures, the researchers sent questionnaires to the children’s parents at both ages, and to their teachers at age eight only. The children also completed a questionnaire on themselves when they were aged 16. Data was excluded for children with intellectual disabilities (IQ scores of 70 or less) or those who did not agree to their data being used. In all, data from 7,871 children was included in the current analysis.
Parents provided information on their children’s hand dominance at age eight by answering a single question about whether the children were right-handed, left-handed or ambidextrous. Parents answered questions about whether the children had any language problems, including whether they had problems with sounds, stuttered or made phonetic mistakes that interfered with learning words. Parents also estimated how their child’s speech compared to that of their peers (four possible answers ranging from ‘clearly weaker’ to ‘better’).
At age eight, teachers reported whether the children had problems with reading, writing or maths, and estimated the standard of their overall school performance (below average, average or above average). At age 16, the children reported on their own school performance in the Finnish language and maths relative to their peers (better than average, average, below average or very poor).
The children’s behaviour at age eight was rated by their teachers, based on a recognised scale. At age 16, their level of ADHD symptoms was assessed using another recognised scale, the Rutter scale. A score above a certain threshold indicated “probable psychiatric disturbance”. Children with the highest 5% of scores on the three ADHD-related parts of the Rutter scale (inattention, hyperactive-impulsive behaviour, or both) were considered to have problems in these areas. The researchers also looked at the severity of each child’s symptoms.
The researchers compared school performance, behaviour, and language difficulties in the group of all non-right-handed children (i.e. left-handed and ambidextrous combined). They then compared all of those who were ambidextrous with those who were right-handed. In their analysis they took into account three factors that could potentially affect the outcomes of the research: gender, birth weight, and gestational age (how far into the pregnancy they were born).
What were the basic results?
The researchers found that of the 7,871 children analysed, the majority (90.9%) were right-handed, 8% were left-handed (632 children), and 1.1% were ambidextrous (87 children). At age eight, 15.3% of the total group of children were reported by their parents to have speech problems. Teachers reported that 9.7% of the children had weaker school performance than their peers, while their teachers’ behaviour assessments suggested that 13.4% had probable psychiatric disturbance. By age 16, problems were reported to be less common.
Based on parental reports at age eight, ambidextrous children were twice as likely as right-handed children to have weaker speaking ability than their peers (odds ratio [OR] 2.44, 95% confidence interval [CI] 1.04 to 5.70). After adjusting for confounding factors that could affect the results, the researchers found no significant differences in other language assessments at age eight.
Reports from teachers suggested that, compared to their peers, ambidextrous children were around twice as likely as right-handed children to have weaker overall school performance (OR 2.16, 95% CI 1.25 to 3.73). After adjusting for potential confounders, there were no significant differences between the groups in behavioural measures at age eight.
At age 16, ambidextrous children were around twice as likely to report that they had poor performance in Finnish language at school compared to right-handed pupils (OR 2.16, 95% CI 1.15 to 4.05). There was no significant difference in their report of maths performance.
There was no significant difference in the proportion of ambidextrous and right-handed children receiving high scores on the hyperactive-impulsive behaviour scale at age 16. However, ambidextrous children were more likely than right-handed children to receive high scores on the inattention and combined inattention/hyperactivity scale (inattention subscale: OR 2.96, 95% CI 1.38 to 6.35; combined subscale: OR 2.67, 95% CI 1.19 to 5.98).
How did the researchers interpret the results?
The researchers concluded that “mixed-handed children have a greater likelihood of having language, scholastic and mental health problems in childhood”, and that “these persist into adolescence”. They say that mixed-handedness could be used to identify children at risk of having persistent problems. More research is needed to explain why there might be a link between hand dominanace and mental health problems.
This research has intriguing findings, but there are a number of limitations to consider:
- The small number of ambidextrous children studied (87) means that the results are more likely to be affected by chance, thus reducing their reliability.
- Although the study took into account some factors that could affect the results (gender, birth weight and gestational age), there are likely to be other confounding factors that could have affected the results.
- It was not clear whether the methods used to assess handedness, language problems and school achievement had been tested and shown to be valid ways of measuring these characteristics. For example, the children’s hand dominance was reported by their parents at age eight, and the presence of individual language problems was only appraised as either ‘yes’, ‘no’ or ‘cannot say’.
- At each age, there was only one source of information about certain aspects of the children’s behaviour and performance (either parents, teachers or the children themselves). Some of the measures used were relatively subjective (for example, problems with language), and their reliability could have been improved by asking more than one source (e.g. the parents and teachers).
- The study carried out a number of statistical tests, which can increase the likelihood that significant differences will be found by chance, and not because a true difference exists.
- Some of the children were scored in the range of “probable psychiatric disturbance”, based on teacher scores of their behaviour. However, this does not necessarily mean that these children would be diagnosed with psychiatric problems if they were assessed by mental health professionals.
The researchers do not think that ambidexterity directly causes the language or behavioural problems seen. Instead, they think that differences in the brain that affect hand dominance could also affect both these traits. At this stage, due to the limitations of this study, its results should be seen as very preliminary, and will require confirmation by other studies. These results should not concern parents who have ambidextrous children.