Each calculation contains data extending before and after the central age (except for the very first and last in the sequence); models centered one year apart share at least 86% of their data and models two years apart share at least 75%, so that there is considerable overlap in the data used for calculation in nearby ages. The regression is weighted by a function of distance of the observation from the central age, so that observations near the central age count more in determining the result than observations further away from the central age. Each of the six dependent variables, the theta ERO power values at each of the three scalp locations (electrodes) for each modality, is modeled separately in order to simplify the interpretation of the regression analysis. This methodology is adapted from the work of Cleveland (1979); Cleveland and Devlin (1988); Gasser et al. (1984a,b); Ramsay and Silverman (2002); Gasser et al. (2004); Molinari and Gasser (2004).
