Digit Preference and Biased Conclusions in Cardiac Arrest Studies

IntroductionIn cardiac arrest (CA), time is directly predictive of patient prognosis. The increase in mortality resulting from delayed cardiopulmonary resuscitation has been quantified minute by minute. Times reported in such a situation could reflect a bias referred to as “digit preference”. This phenomenon leads to privilege certain numerical values (like 2, 5, or 10) over others (like 13). We investigated this bias in times reported during cardiac arrest management in a national register. MethodsWe analyzed data from the French National Electronic Registry of Cardiac Arrests. All the data, including the twelve times corresponding to the main steps of the management of cardiac arrest are prospectively reported by the emergency physician who managed the patients in prehospital settings. The frequency of times as multiples of 15 (0, 15, 30, and 45) was our primary end-point.Results 47,211 times related to 6,131 cardiac arrests were analyzed. The most overrepresented numbers were: 0, with 3,737 occurrences (8% vs 2% expected, p<0,0001) and 30, with 2,807 occurrences (6% vs 2% expected, p<0,0001). Times as multiples of 5 and 10 were overrepresented (52% vs 20% and 10% expected, p<0,0001).ConclusionProspectively collected time were considerably influenced by digit preference phenomenon. Studies that are not based on automatic recording of times as well as studies that have not evaluated and considered this bias should be interpretated with caution.