Data from the analyses of reference samples often must be used to determine the quality of the data being produced by laboratories that routinely make chemical analyses of environmental samples. When a laboratory analyzes many reference samples, binomial distributions can be used in evaluating laboratory performance. The number of standard deviations (that is, the difference between the reported value and most probable value divided by the theoretical standard deviation) is calculated for each analysis. Individual values exceeding two standard deviations are considered unacceptable, and a binomial distribution is used to determine if overall performance is satisfactory or unsatisfactory. Similarly, analytical bias is examined by applying a binomial distribution to the number of positive and negative standard deviations.