ESTIMATING ACTUAL RATES OF DRUG-USE

An increasing number of business and public sector employers are requi ring drug tests of employees and applicants, and tests often are condu cted on other groups as well. One outcome of widespread testing is the tendency to equate the rate of positive drug test results with the ac tual usage mte for the target population involved. In this paper, we s how that these two rates seldom are equal. We develop a simple model t hat may be used to determine the actual rate of drug usage in a given environment, based on drug test rates (reported rates) and laboratory drug testing accuracy. We use recent data on drug test outcomes and la boratory accuracy to illustrate the procedure. The results suggest tha t the highest reported rates underestimate the actual rates; specifica lly, the actual rates are 3-15% higher than the reported rates. Simila rly, the lowest reported rates overestimate the actual rates; specific ally, the actual rates are 10-55% lower than the reported rates. It is not possible to determine the exact degree of mis-estimation for a pa rticular case without knowing the applicable test rate and lab accurac y level, but the aforementioned ranges give an indication of the possi bilities.