Several of my latest posts addressed evidence that challenged some of my long held beliefs about the relative value of parenting style on child outcomes such as mental ability and happiness. In Ten Best Parenting Tips: But does it really matter? I challenged a recently published study in Scientific American: MIND touting the “ten best” parenting tips. The relationship between parent reported child outcomes and parenting behaviors was measured using a correlation coefficient. The author did not, however, control for heredity. It is well known that genes play out in the expression of personality type and a broad array of complex behaviors. So why would it not play out in the happiness, health and functioning capacity of children? If you don’t control for heritability is it not possible that well functioning adults might just pop out well functioning kids? Well it certainly is! And might we wrongly attribute parenting style for something actually under the influence of genes? Yes indeed!
I then explored Does Parenting Style Really Matter? and suggested that the current research from behavioral genetics provides a great deal of evidence concluding that the home environment, as it is influenced by parents, accounts for 0 to 10% of the variance in the personality and intelligence outcomes of children. Heredity (genes) accounts for about 50% and the child’s peer group accounts for the remaining 40-50% of the variance (Pinker, 2002).
The major problem with the above referenced data has been the admitted narrowness with regard to the age and Social Economic Status (SES) of the participants. For the most part, the studies on twins and adopted children were conducted on middle class families with little relative diversity. On top of that, there is a dearth of research focusing on early childhood. This narrowness limits the generalization of findings across different populations and across age levels. Clearly, it is conceivable that parenting style will have varying levels of influence on child outcomes across the developmental lifespan. Over-generalization may lead to faulty thinking and thus very dangerous policy decisions.
Throughout my training and subsequent professional development, as a psychologist, I have been exposed to data suggesting that there is a fairly strong positive correlation between Social Economic Status (SES) and mental ability. The same is true with regard to academic achievement. The underlying message had always been that environmental determinates were responsible for these correlations. Again, the problem with this thinking is that the research upon which such beliefs were formed has largely lacked appropriate controls for heritability. Correlation is not causation and all that jazz!
So what happens to the data when children across the SES spectrum are assessed using techniques that control for genes? One particular study from 2003 suggested that “the heritability of cognitive ability in 7-year-old twins was only 10% in low-SES families but was 72% in high-SES families.” (Tucker-Drob, Rhemtulla, Harden, Turkmeimer & Fask, 2011) This suggests that the environment, including perhaps parenting style and experiential deprivation, play a much bigger role in hindering cognitive development in low SES children versus higher SES children. Further research has found similar, although not so striking, SES differences. Regardless, research within the field of behavioral genetics “suggests that the environment plays a substantial role in the expression of genetic variance in cognitive ability over the course of child development” (Tucker-Drob, et al., 2011). Regardless, questions persist about the degree of influence SES plays in mental ability outcomes and about what point in time the shared environment might affect development.
In a new study just published in Psychological Science by Tucker-Drob, et al. (2011) the authors looked at the mental ability of 750 twins (25% identical, 35% same sex fraternal, and 40% opposite sex fraternal), at 10- and 24-months of age. This sample closely represented US population statistics including a diverse cross section of children across the SES and racial spectrum. And the results were quite different.
At ten months of age, the authors report that the shared environment (the home) played the dominate role in the variance of mental ability scores in all households – rich or poor. There was very little apparent variation in mental ability attributable to heredity. At 24-months however, things get a little more complicated. For low SES children, the environment remains the key variable associated with differences in mental ability. Perhaps as much of 70% of the variance in mental ability is attributable to the shared home environment. While for high SES children, genes become the predominant variable associated with the differences in mental ability scores. Environment still plays a role but much less so. Smart parents have smart kids unhampered by environmental constraints.
Looking at ability gains within individuals between the first assessment at ten months and the retest at 24 months, the high SES children made more gains than those from low SES homes. The difference was modest; however, a child in poverty is likely, simply as a function of SES, to score one standard deviation below a very well to do child on the mental ability test.
These findings suggest that for very young children, environment matters a great deal. This is particularly true for infants rich or poor; but it becomes much more important for poor toddlers. Poor kids are more vulnerable to the adversity associated with deprivation. Many factors have been examined in order to explain this discrepancy. The author of this current study wrote:
“…compared with higher-SES parents, lower-SES parents spend less time with their children (Guryan, Hurst, & Kearney, 2008), are less able to allocate time spent with children in accordance with their children’s developmental needs (Kalil, Ryan, & Corey, 2010), and are less sensitive in responding to their children’s signals (Bradley & Corwyn, 2002; De Wolff & Ijzendoorn, 1997).” (Tucker-Drob, et al., 2011).
One particularly illuminating study published by Hart and Risley in 1995 reported “that at age 3, children in professional families heard an average of 2153 words per hour, while children in working class families heard 1251 words per hour and children in welfare families heard only 616 words per hour. In professional families, parents not only talked more but also used more different words and provided a greater richness of nouns, modifiers and verbs. Parents spent a lot of time and effort asking their children questions, affirming and expanding their responses and encouraging their children to listen and notice how words relate and refer in order to prepare their children for a culture focusing on ‘‘symbols and analytic problem solving’’ (see Hart and Risley, 44 p 133). On the other hand, parents on welfare spent less time talking while they more frequently initiated topics and used more imperatives and prohibitions. These parents were more concerned with established customs such as obedience, politeness and conformity. Working-class families showed a mixture of the two cultures using imperatives and prohibitives while using rich language to label, relate and discuss objects.” (Duursma, Augustyn, & Zuckerman, 2008) The net effect is that poor children hear 30 million fewer words than do children of professionals by the time they reach their forth birthday.
The implications of these differences are profound. Replication of this research is necessary, but we also need greater clarification of the environmental attributes that culminate in the mental ability discrepancies. Should these SES differences stand up to the rigors of scientific scrutiny through replication it will be absolutely essential to invest further in early childhood programs. Jonah Lehrer (2011) likewise noted that: “Such statistics have led many researchers to highlight the importance of improving the early-childhood environments of poor children. Economists such as James Heckman, a Nobel laureate at the University of Chicago, have long advocated for increased investments in preschool education, but this latest study suggests that interventions need to begin even earlier. One possible model is the “Baby College” administered by the Harlem Children’s Zone, which seeks to equip brand-new parents with better parenting skills.”
These findings also reinforce the importance of programs such as Head Start and particularly Early Head Start. It is concerning that these very programs are often the most vulnerable to budget cuts in difficult times. I can’t help but wonder if we would prioritize early childhood development differently if the masses and our politicians were truly aware of these issues. Perhaps we should learn more about this and help spread the word to friends, family, and our representatives. Are we as a society really willing to passively submit to this self perpetuating cycle of poverty?
Duursma, E., Augusta, M., & Zuckerman, B. (2008). Reading Aloud to Children: The Evidence. Archives of Disease in Childhood. Vol 93 No 7.
Epstein, R. (2010). What Makes a Good Parent? Scientific American MIND. November/December 2010. (pgs 46-51).
Hart, B. & Risley, T. (1995). Meaningful differences in the everyday experience of young American children. Baltimore: Paul H. Brookes Publishing.
Lehrer, J. (2011). Why Rich Parents Don’t Matter. Wall Street Journal.com. 1/22/11
Pinker, S. (2002). The Blank Slate: The Modern Denial of Human Nature. New York: Penguin Books.
Tucker-Drob, E. M., Rhemtulla, M., Harden, K. P., Turkheimer, E., & Fask, D. (2011). Emergence of a Gene × Socioeconomic Status Interaction on Infant Mental Ability Between 10 Months and 2 Years. Psychological Science. 22(1) 125–133.