How Can We Best Evaluate The Impact Of Public Health Legislation? Use Of Interrupted Time Series Analysis To Investigate The Introduction Of Tobacco Plain Packaging Legislation In Australia
Robust evaluation of the impact of new legislation or whole-of-population policy initiatives is challenging. With randomized trials unlikely to be feasible in this context and the lack of appropriate control groups, it is difficult to distinguish the effect of a new policy from other potential confounding factors. Furthermore, population-level data for key outcomes may not be available. This study aimed to investigate whether the introduction of tobacco plain packaging in Australia from 1 October 2013 was associated with a change in smokers’ behaviour as measured by the number of calls to the smoking cessation helpline (Quitline). As a comparison, changes in call volume were assessed for the introduction of another tobacco packaging policy, namely the introduction of graphic health warnings from 1 March, 2006.
A whole-of-population study using an interrupted time series analysis was conducted. The population comprised residents of New South Wales and the Australian Capital Territory between 1 March 2005 and 1 April 2013. The main outcome measure was weekly number of calls to the Quitline. Autoregressive integrated moving average (ARIMA) modelling was used to investigate changes in weekly call volume over time while accounting for potential confounders (seasonal trends, anti-tobacco advertising, cigarette costliness and the number of smokers in the community).
There was a 78% increase in calls associated with the introduction of plain packaging (baseline: 363/week; peak 651/week (95% CI 523 to 780/week; p<0.001)). This peak occurred four weeks after the initial appearance of plain packaging and the increase lasted for 43 weeks. The 2006 introduction of graphic health warnings had the same relative increase in calls (84%, baseline: 910/week; peak 1673/week (95% CI 1383 to 1963/week; p<0.001)) but was of shorter duration (20 weeks).
Interrupted time series methods demonstrated a sustained increase in calls to the Quitline after the introduction of tobacco plain packaging that was not attributable to known confounders. Tobacco plain packaging is an important incremental step in comprehensive tobacco control.