As estimate of the validity of drug use survey (DUS) quantity/frequency estimates was obtained by comparing DUS ratings for substances with criteria identified as strongly heritable in work of Tsuang and colleagues [102] “never used, used fewer than 5 times, and used more than 5 times”. All individuals who denied using alcohol, cocaine, heroin, cannabis or nicotine when questioned as part of the addiction severity index screening received “0" scores on the DUS for the appropriate substance. All but two of the individuals who scored 2+ or 3+ on the DUS reported use more than 5 times with a separate instrument on a separate occasion. One individual who reported use of a substance five or fewer times during screening obtained a 2+ and one a 3+ score on the DUS for cannabis. Individuals who reported 1–5 lifetime uses during screening with the addiction severity index received 1+ DUS ratings on several occasions. The fraction of individuals who were rated as 1+ on DUS and who reported use of substances between one and 5 times on a different scale was 7%, 12%, 24%, 32% and 39% for alcohol, nicotine, cocaine, cannabis and heroin, respectively.
