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Richard J. Hickey, PhD
The Wharton School University of Pennsylvania Philadelphia

JAMA. 1985;254(10):1311-1312.

	Since this article does not have an abstract, we have provided the first 150 words of the full text PDF and any section headings.

To the Editor.—

It is not clear in the letters by Berman and Hogue¹ and by Sexton and Hebel² concerning the relationship between maternal cigarette smoking and infant birth weight that the authors understand that biologic causality cannot be established by statistical evidence alone.^3,4 Correctly used, statistical methods can reject hypotheses, but they can never validate them.³ We noted a positive association between maternal prepregnant weight and mean birth weight and also between maternal height and mean birth weight.⁴ Furthermore, it was suggested⁴ that the arbitrary 2,500-g birth weight "break-point" criterion between presumably healthy and unhealthy infants is surely an oversimplification. If both parents are, say, 160 cm (5 ft 3 in) tall or less and weigh 58.8 kg (130 lb) or less, as compared with parents 178 cm (5 ft 10 in) tall or taller and weighing 72.3 kg (160 lb) or more, . . . [Full Text PDF of this Article]

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