many people graduate beyond the use of cocaine to crack
Cocaine is a gateway drug to crack?
According to this NSDUH study (http://www.oas.samhsa.gov/NSDUH/2k9NSDUH/2k9Results.htm):
In, 2009, there were 617,000 people, aged 12 years or older, who used cocaine for the first time. During that same period, 94,000 tried crack for the first time.
If many people 'graduate' beyond the use of cocaine, I would expect I larger number of first-time crack smokers.