What is Meant By
The 'Best Available' Evidence?




best-evidence-smallDecision-making processes are enhanced through the use of valid and reliable evidence. For this reason we use evidence quite automatically and unconsciously for even the smallest of decisions, whether it’s buying someone a birthday present or wondering where to go out for dinner. In most cases we actively seek out to obtain information to support our decision, such as the opinion of our partner, the experiences of friends, or the comments of a local newspaper’s critic. Sometimes this information is so weak that it is hardly convincing at all, in other times the information is so strong that no one doubts its correctness.


It is therefore important to be able to determine which evidence is the ‘best’ – that is, the most valid and reliable – evidence. For instance, the most valid and reliable information on which holiday destination has the least chance of rain in Ireland in early August will obviously come from statistics on the average rainfall per month, not from the personal experience of a colleague who visited the country only once. The same counts for managerial decisions. When making a decision whether or not to use Six Sigma to reduce medical errors in a British university hospital, information such as the outcome of a controlled, longitudinal study with a sample of 150 European university hospitals is more valid and reliable than the personal experience of a colleague who works at small private hospital in Singapore.


The ‘best’ evidence, however, is not always available. Instead of several controlled, longitudinal studies, sometimes there is only a single case study available. In that situation that case study is the best available scientific evidence. In many cases, there is even no scientific or organizational evidence available, so we have no option but to make a decision based on the personal experience of colleague’s. In those cases, some (experiential) evidence is still better than no evidence at all.


One type of decisions that can be considered to be a unique category are so-called self-evident decisions. These decisions are based on logical rather than empirical analysis of a situation. Examples include the decision to apply a tourniquet for a gushing wound or to provide a soldier with a parachute when he jumps out of a plane. Such decisions don’t require scientific evidence to demonstrate efficacy; indeed, a randomized controlled study would be considered very unethical.