aweights, or analytic weights, are weights that are inversely proportional to the variance of an observation;
        that is, the variance of the jth observation is assumed to be sigma^2/w_j, where w_j are the weights.
        Typically, the observations represent averages and the weights are the number of elements that gave rise to
        the average.  For most Stata commands, the recorded scale of aweights is irrelevant; Stata internally rescales
        them to sum to N, the number of observations in your data, when it uses them.