Planning and Assessment of Activity Budget Studies Employing Instantaneous Sampling

To obtain accurate estimates of activity budget parameters, samples must be unbiased and precise. Many researchers have considered how biased data may affect their ability to draw conclusions and examined ways to decrease bias in sampling efforts, but few have addressed the implications of not considering estimate precision. We propose a method to assess whether the number of instantaneous samples collected is sufficient to obtain precise activity budget parameter estimates. We draw on sampling theory to determine the number of observations per animal required to reach a desired bound on the error of estimation based on a stratified random sample, with individual animals acting as strata. We also discuss the optimal balance between the number of individuals sampled and the number of observations sampled per individual for a variety of sampling conditions. We present an empirical dataset on pronghorn (Antilocapra americana) as an example of the utility of the method. The required numbers of observation to reach precise estimates for pronghorn varied between common and rare behaviors, but precise estimates were achieved with <255 observations per individual for common behaviors. The two most apparent factors affecting the required number of observations for precise estimates were the number of individuals sampled and the complexity of the activity budget. This technique takes into account variation associated with individual activity budgets and population variation in activity budget parameter estimates, and helps to ensure that estimates are precise. The method can also be used for planning future sampling efforts.