In research described in the text, Niedenthal and others (2012) related pacifier use during infancy to impaired socioemotional development later on. However, the researchers stated that “the studies

In research described in the text, Niedenthal and others (2012) related pacifier use during infancy to impaired socioemotional development later on. However, the researchers stated that “the studies . . . do not allow causal conclusions, as the children were not randomly assigned to pacifier use.” Based on this information, one can infer that the studies were _____, rather than _____.