Has the minimum legal drinking age been lowered before? What were the results of that "natural experiment"?

"Between 1970 and 1975, 29 states lowered their minimum drinking ages. Meanwhile, 13 states kept the legal age at 21." Researchers found a marked increase in alcohol-related teen car crashes in the states with reductions. "Once the 21 age was restored…alcohol-involved highway crashes immediately declined in this age group." (Wagenaar, A. in Mothers Against Drunk Driving (MADD). (2004, Spring). ―21‖ turns 20. DRIVEN Magazine. http://www.madd.org/getattachment/c7548643-ced8-47b6-8fd5-b0f92d00e9df/-...)

New Zealand lowered its minimum purchase age for alcohol from 20 to 18 in 1999. Researchers noted in 2006 that "…significantly more alcohol-involved crashes occurred among 15- to 19-year-olds than would have occurred had the purchase age not been reduced to 18 years. The effect size for 18- to 19-year-olds is remarkable given the legal exceptions to the pre-1999 law and its poor enforcement." (Kypri, K., Voas, R., Langley, J., Stephenson, B., Begg, D., Tippetts, S., & Davie, G. (2006). Minimum purchasing age for alcohol and traffic crash injuries among 15- to 19-year-olds in New Zealand. American Journal of Public Health, 96(1), 126–131.)

After the minimum age was lowered, New Zealand researchers found that this change in the minimum drinking age "…has resulted in increased presentations to the [central city emergency department] of intoxicated eighteen and nineteen year olds. A similar trend was seen in the 15-17 year olds." (Everitt, R., & Jones, P. (2002). Changing the minimum legal drinking age—its effect on a central city emergency department. The New Zealand Medical Journal, 115(1146), 9–11.) Rates of drunk driving and disorderly conduct have also increased. (Join Together Research Summary: http://www.jointogether.org/news/research/summaries/2007/alcohol-crashes...)