Sir.—During the last 60 years, our perceptions of thumb-sucking have changed radically. In the 1920s, infant care advisers warned that sucking could, among other things, cause malocclusion, digestive upset, inflamed adenoids, infection, drooling, and nail biting. By 1960, however, advisers had adopted a permissive stance toward sucking.
Did scientific evidence lead to this change? A review of the advice literature of the period suggests not. Several researchers have drawn attention to the surprising lack of scientific studies of thumb-sucking.1-3 Instead, advice seems to have been based on unproved ideas in the literature, or on the writer's personal impressions.
But did advisers tell their readers that most of their advice was opinion? To gain some insight into this question, I examined 29 advice books published between 1920 and 1970 (the list is available on request). Did these books tell their readers that their advice on thumb-sucking was largely opinion?