There are multiple approaches to measuring physical activity. Among these are direct observation, electronic monitoring, direct and indirect calorimetry, and self-report instruments. Self-report instruments are the most practical and cost effective option for use with a large group. In a study by Motl, Dishman, Dowda, and Pate (2004), two groups of adolescent girls were assessed using the three-day physical activity recall (3DPAR). The 3DPAR is designed to give estimates of an individual's participation in moderate and vigorous physical activity. The participants in the two groups were eighth- and ninth-grade girls from selected schools in South Carolina. The mean ages of the two groups of girls were similar, as was the distribution of races among the two groups. Data collectors received three months of training and used scripts and specific protocols to collect responses from the participants. The results indicated that moderate and vigorous physical activity measures are independent from one another. Findings showed that weekend vigorous physical activity may be more variable than weekday vigorous physical activity. Additionally, the study found that a higher variance in vigorous physical activity performed during the weekend was harder to explain over a period of time.