A randomized controlled trial was conducted in Denmark between 2012 and 2013. The study collected data from 6793 regular cyclists for a year. The results suggest that conspicuity enhancing jackets can reduce by 47% the risk of collisions with other road users that cause injury and 55% for those collisions involving a motor vehicle. The effect of the intervention was higher in winter compared to summer (56% vs 39%), in daylight (51% vs the overall effect 47%) and for those participants who reported 'high' use of the jackets vs 'low' use (60% vs 33%). The study was based on participants self-reporting data, and there was evidence of response bias, which the authors attempt to correct for, reducing the 47% figure to 38%.