Increasing the frequency of stuttering.

Information about the conditions under which stuttering varies should include variables that both increase as well as decrease stuttering. Most investigations in which the research factors have been under experimental control have focused on decreasing rather than increasing stuttering. This literature review of conditions that might be expected to increase stuttering reveals that most investigators have not been able to raise stuttering frequency above control or base levels. Although some variables may increase stuttering, the research is too meager to speculate about underlying factors.