Participants in the self-affirmation arm write about their most important value, reasons why is important and an example of when they enacted that value. This is the Self-affirmation manipulation task as described in the intervention.

Participants in this arm complete a control equivalent of the self-affirmation task, where they write about their least important value, reasons why is may be important to someone else and an example of when another person may have enacted that value. This is the Control task as described in the intervention.

Participants in the self-affirmation condition indicate their most important value, give three examples of why this value is important to them and one example of something they had done to demonstrate its importance.

Seven days after the intervention, participants are contacted and asked to report their alcohol consumption over the previous 7-day period via self-report items. Participants report the type of alcohol (e.g., beer, spirit), type of container (e.g., small glass, pint, single measure) and the number of each type of drink they had consumed on each day over the previous 7 days using the adapted version (Armitage, Harris, & Arden, 2011) of the timeline fallback technique (Sobell & Sobell, 1992). The total number of units consumed by each participant was then calculated using the UK NHS alcohol unit calculator (NHS Choices, 2013: www.nhs.uk/tools/pages/alcohol-unit-calculator.aspx).

Measures to assess whether the intervention affected the extent to which people accepted information about the risks of alcohol consumption were taken immediately after the intervention via self-report items. Acceptance items included personal relevance, negative affect, attitudes, anticipated regret and intentions. Responses to items were given on 7-point scales with relevant anchors (e.g. strongly disagree [1] to strongly agree [7]). A mean score was calculated for each participant on each measure, with higher scores indicating greater levels of that construct.