Reliability in the context of the experiment: A commentary on two articles by Birkimer and Brown.

Two sources of variability must each be considered when examining change in level between two sets of data obtained by human observers; namely, variance within data sets (phases) and variability attributed to each data point (reliability). Birkimer and Brown (1979a, 1979b) have suggested that both chance levels and disagreement bands be considered in examining observer reliability and have made both methods more accessible to researchers. By clarifying and extending Birkimer and Brown's papers, a system is developed using observer agreement to determine the data point variability and thus to check the adequacy of obtained data within the experimental context.