Standard deviation The values represent the standard deviation of a set of observations made over a time interval. Standard deviation computed using the unbiased formula SQRT(SUM((Xi-mean)^2)/(n-1)) are preferred. The specific formula used to compute variance can be noted in the methods description. Adapted from CUAHSI HIS DataTypeCV. See http://his.cuahsi.org/mastercvreg/edit_cv11.aspx?tbl=DataTy ODM2 Aggregation Statistic Controlled Vocabulary ODM2 Working Group A vocabulary for describing the calculated statistic associated with recorded observations. The aggregation statistic is calculated over the time aggregation interval associated with the recorded observation.