This report, which is part of a two-volume set, documents the results of a study to evaluate and quantify the variability of pavement distress data collected in the Long-Term Pavement Performance (LTPP) program. Analysis were performed on both manual and film~derived distress data. General trends of the distress data were first investigated, followed by statistical analyses of repeatability and detection of variability sources. Distress data bias and precision were also quantified. In addition, a comparison of variability between manual and film-derived distress data was conducted. This report will be of interest to engineers involved in pavement design, pavement performance evaluation and prediction, and pavement maintenance and rehabilitation.