This is a two-stage adaptive parallel group RCT in which Australian smokers who usually purchase packs containing ≥25 cigarettes were randomised to use only packs containing 20 cigarettes (intervention) (n = 40) or their usual pack size (control) (n = 39) for four weeks. The primary outcome, the average number of cigarettes smoked per day, was measured through collecting all finished cigarette packs, labelled with the number of cigarettes participants smoked. Secondary outcomes included: Heaviness of smoking, motivation to stop smoking and autonomy over smoking.

Comparisons in the primary and secondary outcomes were made between study arms using general linear models in the standard analysis. The interim analysis was used for a sample size re-estimation when 124 participants had completed the study. A preregistered protocol and statistical analysis plan can be found here: https://osf.io/g45zn/.

The deposit includes the following files: CigPackSizeStudy_Protocol_20181203 CigPackSizeStuy_AdditionalFile2_MissingandInconsistentData_20190430 CigPackSizeStudy_DataDictionary_20210618

As well as (which were used during the standard analysis): CigPackSizeStudy_SAP_20190611 CigPackSizeStudy_PackLevelData_v1.0_20190405 CigPackSizeStudy_ParticipantLevelData_20190405 CigPackSizeStudy_RecodingImputingAndMerging_20190405 CigPackSizeStudy_AnalysisCode_20190405

And (which were used for the interim analysis): CigPackSizeStudy_InterimAnalysis_HSIQ2_20190211 CigPackSizeStudy_InterimAnalysis_PackLevelData_20190211 CigPackSizeStudy_InterimAnalysis_ParticipantLevelData_20190211 CigPackSizeStudy_InterimAnalysisCode_R_vs4_20190211

The data dictionary defines the contents of all data files (pack and participant level, and standard and interim analysis) comprehensively and can be opened in Microsoft Excel.

Data files can also be opened in Microsoft Excel.