Speech outcome following treatment in cross-linguistic cleft palate studies: Methodological implications

Objective: In cross-linguistic studies of cleft palate speech outcome following treatment, treatment is the independent variable, speech outcome is the dependent variable, and the speakers' language background is a background variable, like sex, age, and cleft type, which must be eliminated. This article focuses on language as a background variable and how it should be treated. The methodological problems are illustrated through a presentation of two cross-linguistic speech outcome studies. Conclusion: When speakers of different language background are included in cleft palate studies of speech outcome following treatment, speech outcome data should be based on speech units that are phonetically identical across languages. This affects the make-up of the speech material used in the study. In practice, the requirement of phonetically identical speech units may not be totally met, and detailed information regarding the interaction between the cleft condition and speech sound production is still required to fully understand how the validity of data is affected if this requirement is not met.