RT Journal
A1 Pletcher MJ, Kertesz SG
T1 LOng-term marijuana use and pulmonary function—reply
JF JAMA
JO JAMA
YR 2012
FD May 2
VO 307
IS 17
SP 1796
OP 1797
DO 10.1001/jama.2012.3607
UL http://dx.doi.org/10.1001/jama.2012.3607
AB 
In Reply: As noted by Drs Patel and Khazeni, accurately measuring long-term exposure to marijuana is inherently difficult and may be made more difficult by cognitive problems with recollection caused by heavy regular marijuana use. However, we used measurements collected prospectively at the periodic study visits made during the 20-year follow-up in the CARDIA study. At each study visit, participants were asked about current/recent usage (“ . . . in the last 30 days”), and we made the assumption that use between examinations reflected use reported at each examination. While these assumptions introduce measurement error, they do not depend on long-term recollections about total usage over the course of many years. Also, the CARDIA study did not collect information about mode of inhalation (joint, bong, vaporizer, etc), so we could not conduct the subgroup analyses suggested by Patel and Khazeni.