Average content of ecstasy tablets was measured through gathering data from 136 samples of ecstasy tablets obtained from police seizures in the Northwest of England that were analyzed by the UK Forensic Science Unit during 2001, and from 80 tablets randomly selected from a seizure of 160,000 "White Dove" tablets. The "White Dove" sample was found in 8 bags, and 10 tablets from each bag were analyzed. Contents of both samples were determined using HPLC-DAD, and results compared with past studies examining ecstasy tablet contents. The mean MDMA content of tablets seized in the northwest of England in 2001 was 61-69 mg MDMA, with most tablets containing between 40 and 90 mg MDMA. Eight samples also contained MDE (3,4-methylenedioxyethylamphetamine). Mean MDMA contents of the 80 "White Dove" tablets was 78.8 mg and ranged from 73 to 89 mg. There were no significant differences in content by bag, but there was a significant correlation between tablet weight and MDMA content in the "White Dove" sample. The authors note that in this analysis and in others, tablets stamped with the same symbol (e.g. "Mitsubishi") showed wide variance in MDMA content, indicating that tablet "brand" is not a good indicator of content. MDMA content appears to have declined from the early 1990s, when it ranged from 88 to 103 mg. The authors note that other papers have found a greater number of tablets containing substances other than MDMA, including MDA, MDE (MDEA), amphetamine and ketamine. This suggests that samples drawn from drug seizures may overestimate ecstasy purity, while studies based on user-submitted samples may underestimate ecstasy purity. Cole and colleagues suggest that studies of ecstasy users should take into account variance in MDMA content over time in evaluating relationships between extent of lifetime use (such as lifetime consumption) and long-term effects, Since individuals reporting having taken the same number of tablets may have consumed different doses of MDMA.