Derivation of adherence metrics from electronic dosing records

Numerous adherence variables have been created from electronic dosing recor ds hindering synthesis of the vast body of adherence research. To elucidate the mathematical foundation for electronic adherence monitoring and to und erstand how diverse electronic adherence metrics are related to each other and the underlying construct of adherence behavior. Several representative adherence metrics are derived mathematically and their relationship to the underlying consumption (or dosing event) rate analyzed. Data from a 3-month study of 286 individuals on single-drug antihypertensive therapy are then used to empirically study the statistical properties of several of these el ectronic adherence metrics. As suggested by their common link to the consum ption (or dosing event) rate, the analyzed electronic adherence metrics wer e generally strongly correlated (r <-.6 and > .4). The lowest correlation ( r =.15) involved the ratio of the observed number of doses to the recommend ed number (called average adherence), which tended to emphasize quantity co nsumed, and the ratio of the observed to maximum mean squared rate deviatio n (MSRD ratio), which focused more on dose timing. Despite their different formulations, electronic adherence variables are generally closely correlat ed. Adherence metrics that average the consumption rate over multiple doses (by summing up the number of doses and dividing by the monitored time) may be less sensitive to short-term fluctuations in medication intake. Metrics that are more sensitive to timing variability may thus be preferable when timing as well as quantity of dosing are of interest. (C) 2001 Elsevier Sci ence Inc. Although reserved.