Single studies often make headlines, but are risky as a foundation of parenting. Parents can have more confidence in ideas that have been well-tested and verified through a considerable amount of scientific research, involving more than a single study or author. For instance, while Grandma knew that loving and caring parents are critical for a child's development, every study I know of has found some connection between parental love and positive outcomes for kids. While it isn't the only important factor in parenting, you can't go wrong being a loving, supportive parent. It's important for parents to trust their own feelings.
Parents are the experts on their individual children and parenting situations.
Regardless of how highly respected the source, parents are wise to carefully evaluate information they read and hear against their own values, instincts and experiences before making decisions about its usefulness. Part of assessing the validity of an idea is to test it out in our own life. Of course, no one strategy works for all parents, with all children, under all circumstances. But if a strategy works at all, it becomes a tool we can keep handy to use when we need it. Respected sources will provide suggestions for further reading where similar ideas will be presented and discussed more fully.