AimWe aimed to investigate the effect of compression-only cardiopulmonary resuscitation (CPR) with conventional CPR in patients who were defibrillated by laypersons. MethodsThis is a population-based, nationwide observational study. Adult and children who sustained a witnessed out-of-hospital cardiac arrest and defibrillated by laypersons between 2005 to 2019 were identified on the national database. The study used trend analyses, multivariate logistic regression, and inverse probability weighting using propensity score to explore changes in one-month survival and survival with a good neurological outcome over time and the influence of compression-only CPR compared with conventional CPR. ResultsIn total, 11,402 patients defibrillated by laypersons were enrolled in this study. The percentages of compression-only resuscitation increased dramatically and more than 50% from 2012 (P < 0.001). The percentages of cases with favorable resuscitation outcomes also increased annually (P < 0.001). By regression analysis, favorable outcomes were associated with recent years, male sex, younger age, and shorter resuscitation start time. In addition, the adjusted odds ratio of compression-only CPR to conventional CPR was 1.23 with a 95% confident interval 1.13–1.34. By inverse probability weighting, compression-only CPR was superior to conventional CPR for the favorable outcomes (P < 0.001). The adjusted outcomes in each year were better in compression-only resuscitation in most of the years. The overall relative risk reduction and the number needed to treat for compression-only resuscitation compared with conventional resuscitation were 7.6% and 22.1, respectively. ConclusionsIn Japan, the outcomes of out-of-hospital cardiac arrest patients who were defibrillated by laypersons were considerably better in compression-only resuscitation of laypersons every year.