This TAPPI Standard Practice provides a procedure for judging whether suspect test determinations should be investigated further for possible rejection. A suspect determination (apparent outlier) is one that appears to deviate markedly from other determinations on the same sample of material. An outlying determination (outlier) is a suspect determination for which the deviation has, in fact, been found to be significant using an appropriate statistical test. Formal treatment of suspect test determinations, as specified in this document, is necessary only in critical situations (e.g., very critical research) or when required by a product specification or an official test method. Formal treatment of suspect test determinations and test results is highly desirable in studies for the investigation of a test method (see TAPPI T 1200 Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility). Both nonstatistical and statistical rules for dealing with suspect test determinations are given. Basically no test determination should be accepted, no matter how correct the value appears to be, if it is known that a faulty determination has been made, and no test determination should be completely rejected purely on a statistical significance test. The statistical tests described in this practice have been selected from a large number that are available. They apply to the simplest kind of experimental data, that is, replicate determinations of some property of a given sample of material.