For the critical outcome survival to hospital discharge—OHCA, we identified very-low-quality evidence (downgraded for indirectness, imprecision, and inconsistency) from 4 observational studies enrolling 6983 patients.(Stiell 1999, 1175; Olasveengen 2007, 427; Fletcher 2008, 127; Task Force on the management ST-segment elevation acute myocardial infarction of the European Society of Cardiology 2012, 2569) One of these studies contributed a disproportional number of patients (6331).(Stiell 1999, 1175) Heterogeneity prevented calculating a pooled effect and limited our confidence in the individual effects. Individual effects appear weakly in favor of quality measurement. For the critical outcome of survival to hospital discharge—in-hospital cardiac arrest (IHCA), we identified low-quality evidence (downgraded for indirectness, imprecision, and inconsistency) from 2 observational studies enrolling 318 patients showing no benefit in survival to hospital discharge (data cannot be pooled).(Edelson 2008, 1063; Wolfe 2014, 1688) One study showed a modest improvement in neurologic outcomes.(Wolfe 2014, 1688) There was very-low-quality evidence (downgraded for indirectness, imprecision, and inconsistency) from 3 observational time-series studies enrolling 105 003 patients.(Rittenberger 2008, 198; Jiang 2010, 1664; Bradley 2012, 1349) One of these studies contributed a disproportional number of patients (104 732).(Bradley 2012, 1349) Heterogeneity prevented calculation of a pooled effect. Individual effects were in favor of quality measurement in 2 studies(Rittenberger 2008, 198; Bradley 2012, 1349) and showed no effect for the third study.(Jiang 2010, 1664) For the important outcome of chest compression depth, we have identified very-low-quality evidence (downgraded for risk of bias and inconsistency) from 3 observational studies enrolling 990 patients.(Olasveengen 2007, 427; Edelson 2008, 1063; Wolfe 2014, 1688) Heterogeneity prevented calculating a pooled effect and limited our confidence in the individual effects. Individual effects appear weakly in favor of quality measurement. For the important outcome of chest compression rate, we identified very-low-quality evidence (downgraded for risk of bias and inconsistency) from 6 observational studies, enrolling 1020 patients in 4 of the studies, and an unreported number in 2 others.(Olasveengen 2007, 427; Edelson 2008, 1063; Fletcher 2008, 127; Jiang 2010, 1664; Clarke 2011, A6; Wolfe 2014, 1688) Heterogeneity prevented calculating a pooled effect and limited our confidence in the individual effects. Three of the studies appear to weakly favor quality measurement, whereas 3 showed no effect. For the important outcome of other system variables, very-low-quality evidence (downgraded for risk of bias, indirectness) from 1 human observational study shows defibrillator-equipped resource response time decreased to 5.3 minutes from 6.7 minutes when an optimization strategy was implemented.(Stiell 1999, 1175) Across studies, the direction of the effect was consistent, and at times the effect size was large and statistically significant. There is no evidence that data collection and feedback are deleterious to patients in any way.