PT - JOURNAL ARTICLE AU - Brian A King TI - The chicken or the egg? The value of longitudinal research in an increasingly diverse tobacco product landscape AID - 10.1136/tobaccocontrol-2020-055694 DP - 2020 May 01 TA - Tobacco Control PG - s131--s133 VI - 29 IP - Suppl 3 4099 - http://tobaccocontrol.bmj.com/content/29/Suppl_3/s131.short 4100 - http://tobaccocontrol.bmj.com/content/29/Suppl_3/s131.full SO - Tob Control2020 May 01; 29