How Much Observation Is Enough?

BACKGROUND: The Systematic Observation of Play and Recreation in Communities (SOPARC) was designed to estimate the number and characteristics of people using neighborhood parks by assessing them 4 times/day, 7 days/week. We tested whether this schedule was adequate and determined the minimum number of observations necessary to provide a robust estimate of park user characteristics and their physical activity levels. METHODS: We conducted observations every hour for 14 hours per day during 1 summer and 1 autumn week in 10 urban neighborhood parks: 2 each in Los Angeles, CA; Albuquerque, NM; Columbus, OH; Durham, NC; and Philadelphia, PA. We counted park users by gender, age group, apparent race/ethnicity, and activity level. We used a standardized Cronbach's alpha and intraclass correlation coefficients to test the reliability of using fewer observations. RESULTS: We observed 76,632 individuals, an average of 547/park/day (range 155–786). Interobserver reliability ranged from 0.80 to 0.99. Obtaining a robust estimate of park user characteristics and their physical activity required a schedule of 4 days/week, 4 times/day. CONCLUSION: An abbreviated schedule of SOPARC was sufficient for estimating park use, park user characteristics, and physical activity. Applying these observation methods can augment physical activity surveillance.