1. Post-It Notes to Improve Questionnaire Response Rates in RCTs Findings from a Randomised Sub-Study Ada Keding 1, Helen Lewis 2, Kate Bosanquet 2, Simon Gilbody 2, David Torgerson 1 1 York Trials Unit, University of York, UK; 2 Department of Health Sciences, University of York, UK Background Valid treatment effect estimates in the analysis of RCTs using patient reported outcomes depend on adequate response rates. Evidence from non-RCT surveys suggests that inexpensive post-it notes may improve response rates. Introduction Methods Aim To assess the effectiveness of a Post-it® note attached to questionnaires on patient response rate and time to response in an elderly mental health study population. Results Post-it® notes were not found to be effective in improving retention in the elderly population of this trial. However, beneficial effects for sub-groups of clinical populations may exist. Conclusions Design A two-arm RCT (CASPER PiN trial) was embedded into the follow-up of older adults as part of the UK Casper + trial and Casper Shard trial At 4 months follow-up of both trials, participants were randomised 1:1 to receive their follow-up questionnaire with or without a post-it note requesting completion Main Analyses Adjusting for age, gender, main trail treatment allocations and depression at baseline, analyses revealed no statistically significant effect of having received a Post-it® note on response rates, time to return or the need for a reminder at three weeks following the initial questionnaire posting. 817 Casper + and Casper Shard Participants in study time window 4-Month Follow-Up 611 Randomised 314 Follow-up questionnaire without post-it note 297 Follow-up questionnaire with post-it note 206 Withdrawn before 4-Month Follow-up Contact @ada.keding@york.ac.uk Ada Keding  York Trials Unit StatisticianDepartment of Health Sciences University of York, York, YO10 5DD, UK Funding: The CASPER+ trial was funded by the National Institute for Health Research HTA programme (project number 10/57/43). This ‘trial within a trial’ was funded by the York Trials Unit. Disclaimer: The views and opinions expressed therein are those of the authors and do not necessarily reflect those of the HTA programme, NIHR, NHS or the Department of Health. Post-it® Note ControlStatisticP-Value Questionnaire Return 89.6%89.8%OR=0.97p=0.913 Median time to return 14 days15 daysHR=1.04p=0.611 Reminder required 30.0%30.9%OR=0.97p=0.875 The Intervention A printed yellow Post-it® note, 3 inches square, attached to the top half of the front page of the questionnaire Signed with the first name of the researcher contact Analysis Questionnaire Return and Need for a Reminder: Logistic regression; Time to Return: Cox proportional hazard model All analyses tested the effect of the intervention while adjusting for treatment arm of the two main Casper trials, depression at baseline, age and gender (interactions with post-it® notes were also explored) Participants Please take a few minutes to complete this for us. Thank you. Jane Post-it® Note Control Mean Age (SD)74.3 (6.83)73.8 (6.27) Female176 (59%)188 (60%) Major Depressive Episode 134 (45%)167 (53%) Subthreshold Depression 163 (55%)147 (47%) Sub-group Analyses An exploratory analysis showed that participants with major depression were more likely, and participants with sub-threshold depression less likely to respond to post-it® notes (p-value of interaction = 0.019). p=0.019 Source Trials Casper + trial: RCT of Collaborative Care versus Usual Care in people aged 65 and over with major depressive episode symptoms Casper Shard trial: RCT of a Guided Self-Help Booklet versus Usual Care in people aged 65 and over with sub-threshold depressive symptoms Table 2: Effect of post-it note allocation on trial outcomes Figure 2: Questionnaire Return by Baseline Depression Table 1: Baseline characteristics Figure 1: Kaplan-Meier plot for time to return