Preliminary research has found that patient factors may contribute to errors—for example, when the patient fails to take medications as prescribed. In this study, focus groups of patients and health care professionals were used to identify and characterize the types of errors that can be committed by patients. The authors identified two main groups of errors: action errors, errors of patient behavior such as failing to attend an appointment, and mental errors, which are errors of patients' thought processes. Included among mental errors are factors that have been linked to errors, such as low health literacy. The authors suggest that further research should investigate how interactions among patients, clinicians, and systems lead to harmful adverse events.