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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.