The reliability of observational data: I. Theories and methods for speech-language pathology.

Much research and clinical work in speech-language pathology depends on the validity and reliability of data gathered through the direct observation of human behavior. This paper reviews several definitions of reliability, concluding that behavior observation data are reliable if they, and the experimental conclusions drawn from them, are not affected by differences among observers or by other variations in the recording context. The theoretical bases of several methods commonly used to estimate reliability for observational data are reviewed, with examples of the use of these methods drawn from a recent volume of the Journal of Speech and Hearing Research (35, 1992). Although most recent research publications in speech-language pathology have addressed the issue of reliability for their observational data to some extent, most reliability estimates do not clearly establish that the data or the experimental conclusions were replicable or unaffected by differences among observers. Suggestions are provided for improving the usefulness of the reliability estimates published in speech-language pathology research.