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Firstly, in one study cited in the article higher scores on the Rotter scale correlated with higher depression scores. However, the scale measures locus of control; it is not a measure of depression and thus is not a valid indicator of prior psychological state or prior depression.

Secondly, women included in the sample were categorised in the analysis according to marital status in 1992, yet data regarding first abortion or first unintended delivery are taken from 1980-92, with abortions and deliveries on average occurring between 1984 and 1986. Marital status in 1992 was not necessarily the marital status of women included in the sample during their first abortion or first unintended delivery. Thus basing the analysis and conclusions on the categories of married versus unmarried women is invalid and is not meaningful.

Given these observations, more rigorous analysis of the data is needed before any conclusions can be drawn about the link between depression and unintended pregnancy and marital status.

EDITOR—Reardon and Cougle claim no conflict of interest in their paper. However, the principal author (Reardon) is a professional anti-abortionist and the funding organisation for which he works has as its primary aim propagandising against abortion. Therefore the sampling, the methods, the statistics, and the conclusions should be rigorously evaluated.

Policy summary:
Breast feeding does not increase children's intelligence
Despite its many advantag es, breast feeding has little effect on children's intelligence. In a cohort study of 3161 mothers and 5475 children, Der and colleagues (p. 945) found that breast feeding was associated with higher IQ in children, but that this effect was almost entirely accounted for by maternal IQ. More intelligent mothers were more likely to breast feed, and maternal IQ was more predictive of feeding choice than mothers' age, education, home environment, and antenatal smoking status, or children's birth weight and birth order.

Reardon and Cougle's study finds that in unmarried women levels of depression do not differ between those who abort their pregnancy and those who carry it to term,(2) which seems to negate the push to limit access to abortion for teenagers. This might well be the most important finding in the study, as enormous effort is placed on limiting teenagers' access to abortion in the United States, where the Elliott Institute is based (www.cpcworld.org/hope-net/CPC/Elliott-Institute.html); this raises doubt about the authors' claim that they have no conflict of interest.

Certainly, this study shows that depression is not a factor in the issue of teenagers obtaining abortions. The authors seek to explain this away, but only with unsubstantiated speculations. If they have so little faith in their result why are they trying to present the study as a factual one?

(1) Major B, Cozzarelli C, Cooper ML, Zubek J, Richards C, Wilhite M, et al. Psychological responses of women after first-trimester abortion. Arch Gen Psychiatry 2000; 57: 777-784[ISI][Medline].

(2) Reardon D, Cougle J. Depression and unintended pregnancy in the national longitudinal survey of youth: a cohort study. BMJ 2002; 324: 151-152.

EDITOR--Reardon and Cougle's paper raises at least three concerns.(1)

Firstly, their analyses do not address the stated hypothesis. No results indicate whether "prior psychological state is equally predictive of subsequent depression among women . . . regardless of whether they abort or carry to term." Nevertheless, their unstated hypothesis, focused on abortion and depressive symptoms, may be the more central question.

Secondly, the final sample of women is surprisingly small. Only 421 of the initial 4463 women reported a first abortion or first unintended delivery between 1980 and 1992. Is it possible that the question in 1992 asking pregnancy intention actually referred to a much narrower time frame (that is, a delivery between the biannual surveys)? Little information is given about the abortion question; it is possible that the index unintended pregnancy defined in 1992 resulted in neither the first abortion nor the first delivery.

Thirdly, the discussion omits mention of possible residual confounding. The national longitudinal survey of youth (NLSY) uses a four item abbreviated version (NLSY Cronbach 0.35) of Rotter's original 60 item locus of control scale, which itself is probably an inadequate proxy for prior psychological state. Furthermore, a one year measure of income may be only a modest proxy for a person's lifetime socioeconomic position. (2,3) The robustness of the authors' findings could be examined with other available measures. For example, the 1980 Rosenberg self esteem scale data (NLSY Cronbach 0.83) and the full 12 years of annual income and family size data would be stronger, though still less than optimal, tests of the hypotheses.

This criticism is not an attempt to dismiss research on the topic; rather, such important and highly content ious questions require published studies with equal degrees of rigour and transparency.

(1) Reardon DC, Cougle JR. Depression and unintended pregnancy in the national longitudinal survey of youth: a cohort study. BMJ 2002; 324: 151-152.

(2) Wolfe B, Haveman R, Ginther D, An CB. The "window problem" in studies of children's attainments: a methodological exploration. J Am Stat Assoc 1996; 91: 970-982[ISI].

(3) Smith GD, Hart C, Blane D, Gillis C, Hawthorne V. Lifetime socioeconomic position and mortality: prospective observational study. BMJ 1997; 314: 547-552.