## KEY POINTS

KEY POINTS

• By randomly distributing patients to the study groups, the potential risk factors in randomized clinical trials are likely to be evenly dispersed.

• Bayesian statistics are an approach for learning from evidence as it accumulates; that is, the Bayes theorem is applied to combine prior information with current information on an outcome of interest and derive a probability.

• The propensity score is the probability of treatment assignment conditional on observed baseline characteristics; that is, each treated patient is matched to one or more control patients with similar propensity scores.

• Relative risk or risk ratio (RR) compares the outcome probability in two groups (ie, with and without an intervention, or with and without a risk factor). When the RR is equal to 1, there is no evidence of effect.

• Odds ratios are good estimates of the RR when the outcome is relatively rare (<20%); however, this is not true when the outcome is more common.

• P value is the probability of obtaining the observed effect (or larger) under the null hypothesis that there is no effect; that is, the P value can be interpreted colloquially as the probability that the finding was the result of chance.

• Bias is the deviation of results due to systematic errors in the research methods and includes selection bias (study groups differ systematically) or observer/information bias (systematic differences in the way information is collected).

Good doctors use both individual clinical expertise and the best available external evidence, and neither alone is enough. Without clinical expertise, practice risks becoming tyrannized by evidence, for even excellent external evidence may be inapplicable to or inappropriate for an individual patient. Without current best evidence, practice risks becoming rapidly out of date, to the detriment of patients.

Sacket et al, 1996

## WHAT IS EVIDENCE-BASED TRAUMA CARE?

Evidence-based medicine (EBM) is “the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.”1 The term evidence-based medicine was coined by a group of physicians at McMaster University in Hamilton, Ontario, in the early 1990s.1,2 EBM is a combination of clinical expertise and best evidence, as eloquently stated by Sacket and colleagues in the quotation at the beginning of this chapter.1 The definition of EBM has two basic components: the first is “the conscientious, explicit, and judicious use,” which, in trauma, applies to split-second decisions in the face of an immense variety of unexpected clinical scenarios. The time pressure and the irreversibility of many surgical procedures enhance the anxiety of decision making. The second component of the EBM definition is “best evidence.” What constitutes “best evidence”? Best evidence is “clinically relevant research,”1 which can both invalidate previously accepted procedures or replace them with new methods that are more powerful, efficacious, safe, and cost containing. In simple words, it comes down to “How does the article I read today change ...

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