Red for danger in systematic reviews

How do you feel about red traffic lights—stop immediately, or the basis for a negotiation? Most people stop most of the time, which is why traffic works—because we obey the rules and we know red means danger. We may not have the statistics at our fingertips but we know that running a red light is a risky business. The USA Federal Highway Administration claims that roughly 45% of car collisions take place at a road intersection and the cause is usually related to ignoring a stop sign or running a red stop light. In 2018, 846 people were killed in the USA and 139 000 injured in crashes involving crossing a red light.1 Initiated in Cochrane reviews, many systematic reviews now use a red–amber–green system in the assessment of the risk of bias relating to the methods used in included studies. Green indicates no known risk of bias, amber (used when an item is not mentioned in a study) an unknown level of risk of bias, and red when a methodological issue is known to be associated with a high risk of bias. Assessment of risk of bias is good, but how that risk of bias … Correspondence to Dr Andrew Moore, Pain Research, Newton Ferrers, Plymouth PL8 1DA, UK; andrew.moore{at}omkltd.org