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Philip Lempert, MD

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

Repka et al¹ observed that "patients who participated had better amblyopic eye visual acuity at the 2-year outcome than patients who did not participate," and identified this as indicating a potential selection bias.

Only 169 of 419 (40%) initial subjects completed the study, while 60% dropped out. Treatment effectiveness could be overestimated because patients who were not improving might have chosen to discontinue participation.

Another form of selection bias is suggested by the relative paucity and variability of the subjects recruited. Amblyopia is a very common condition, and the investigators were actively involved with pediatric ophthalmology. It is likely that many hundreds or thousands of new patients were seen at the clinical sites during the recruitment period. Yet, 13 clinical sites recruited 3 or fewer subjects. Conversely, 7 sites contributed 20 or more subjects. The paucity of subjects and asymmetry of patient enrollment among sites suggests the . . . [Full Text of this Article]

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