Professionals in the discipline of communication sciences and disorders primarily assess and treat speech, language, and hearing disorders. Speech–language pathologists and audiologists are the two professions. These professionals constantly search for ways to improve services for people who have speech, language, or hearing disorders. To do so, these professionals conduct research to figure out the best treatment options for their clients. Two types of research methods, efficacy of treatment studies (efficacy studies) and effectiveness of treatment studies (effectiveness studies), help establish the certainty and practicality of new treatment approaches. Evidence from such studies advances the discipline of communication sciences and disorders and hence this topic is relevant. This entry describes the two types of treatment research methods.