Reliability of single sample experimental designs: comfortable effort level.

This study was designed to ascertain the intrasubject variability across multiple recording sessions-most often disregarded in reporting group mean data or unavailable because of single sample experimental designs. Intrasubject variability was assessed within and across several experimental sessions from measures of speaking fundamental frequency, vocal intensity, and reading rate. Three age groups of men and women--young, middle-aged, and elderly--repeated the vowel /a/, read a standard passage, and spoke extemporaneously during each experimental session. Statistical analyses were performed to assess each speaker's variability from his or her own mean, and that which consistently varied for any one speaking sample type, both within or across days. Results indicated that intrasubject variability was minimal, with approximately 4% of the data exhibiting significant variation across experimental sessions.