Exercise: Effect of breast feeding on intelligence

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. 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 Results The mother's IQ was more highly predictive of breastfeeding status than were her race, education, age, poverty status, smoking, the home environment, or the child's birth weight or birth order. One standard deviation advantage in maternal IQ more than doubled the odds of breast feeding. Before adjustment, breast feeding was associated with an increase of around 4 points in mental ability. Adjustment for maternal intelligence accounted for most of this effect. When fully adjusted for a range of relevant confounders, the effect was small (0.52) and non-significant (95% confidence interval -0.19 to 1.23). The results of the sibling comparisons and meta-analysis corroborated these findings. Conclusions Breast feeding has little or no effect on intelligence in children. While breast feeding has many advantages for the child and mother, enhancement of the child's intelligence is unlikely to be among them. Introduction This question is based on Effectiveness and economic evaluation of a nurse delivered home exercise programme to prevent falls. 1: Randomised controlled trial (Robertson et al. (2001) British Medical Journal 322, 697-701.) Read the paper and answer the questions.

Question 1. The 'mean (SD)' of the number of current prescribed drugs were 3.1 (2.4) and 2.9 (2.3) for the two groups. What does this mean? What does it tell us about the shape of the distribution of the number of prescribed drugs taken?

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Question 2. The authors report 'We found a 46% reduction in the number of falls during the trial for the exercise group compared with the control group (incidence rate ratio 0.54, 95% confidence interval 0.32 to 0.90).' What is a 95% confidence interval? What does this tell us about the difference in incidence of falls?

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Question 3. What might be the effect on the interpretation of the results of some subjects not completing the trial?

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Question 4. There were 9 serious falls in the control group and 2 in the exercise group, P=0.033. What is meant by 'P=0.033'? What does it tell us about the effect of exercise on falls?

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Question 5. In Table 2, P values are only given when the difference is statistically significant. The difference for injurious falls is therefore not statistically significant. What can we conclude from this?

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Question 6. The main conclusion of the paper is 'An individually tailored exercise programme delivered at home can prevent falls.' Do the data support this?

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Last updated: 23 October, 2006.

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