In the late 1970s researchers dispelled the notion that pacifiers were psychologically unhealthy and aberrant. Richard H. Passman and Jane S. Halonen at the University of Wisconsin-Milwaukee traced the developmental course of attachments to pacifiers and provided norms. They found that 66% of their sample of babies who were three months old in the United States demonstrated at least some attachment, according to their mothers. At six months of age, this incidence was 40%, and at nine months it was 44%. Thereafter, the rate of attachment to pacifiers dropped precipitously until, at 24 months of age and later, it was quite rare.