Exercise: Effect of breast feeding on intelligence

To assess the importance of maternal intelligence in the link between breast feeding and children's intelligence, Der et al. (2006) carried out an analysis of data from the 1979 US national longitudinal survey of youth. Data on 5475 children, the offspring of 3161 mothers in the longitudinal survey, were analysed. The main outcome measure was IQ in children. They reported that, after adjustment for maternal intelligence and other variables, the effect of breastfeeding was small (0.52 IQ scale points) and non-significant (95% confidence interval -0.19 to 1.23). They concluded that breast feeding has little or no effect on intelligence in children.

N.B. IQ has mean = 100, SD = 15, by definition.

Reference: Der G, Batty GD, Deary IJ. (2006) Effect of breast feeding on intelligence in children: prospective study, sibling pairs analysis, and meta-analysis. British Medical Journal 333, 945-948.

Questions

Question 1. What do the authors mean by '95% confidence interval -0.19 to 1.23'?

Check suggested answer 1.

Question 2. Why do the authors say that the effect of breastfeeding was 'non-significant' and what does this mean?

Check suggested answer 2.

Question 3. The authors concluded that breast feeding has little or no effect on intelligence in children. Why do they say this?

Check suggested answer 3.

Question 4. Why did the the authors NOT conclude that that breast feeding has no effect on intelligence in children.

Check suggested answer 4.

We shall return to this paper in Week 10.

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Last updated: 12 December, 2006.