In Search of Evidence

Evidence-Based Management: The Basic Principles
approach is more effective than the way managers already typically make decisions.
This is, of course, a very important question. To measure the effect of evidence-based
practice would require an evaluation of a large number of situations and contexts
where evidence-based practice was applied, and the measurement of a wide range of
outcomes, preferably by means of a double blind, randomized controlled study. Such a
study might well be too difficult to carry out. However, there is plenty of scientific
evidence that suggests that taking an evidence-based approach to decisions is more
likely to be effective. We noted earlier in this chapter that the human mind is
susceptible to systematic errors — we have cognitive limits and are prone to biases that
impair the quality of the decisions we make. The fundamental questions to ask include:
How can we make decisions without falling prey to our biases? Are there decision
practices or processes that can improve decision quality? Fortunately, there are a large
number of studies that indicate the following:
• Forecasts or risk assessments based on the aggregated (averaged) professional
experience of many people are more accurate than forecasts based on one person’s
personal experience (provided that the forecasts are made independently before
being combined) (Bauer, 2003; Scott Armstrong, 2001; Servan-Schreiber, 2004;
Silver, 2012; Yaniv & Choshen-Hillel, 2012)
• Professional judgments based on hard data or statistical models are more accurate
than judgments based on individual experience (Ayres, 2007; Grove, 2005; Lewis,
2003)
• Knowledge derived from scientific evidence is more accurate than the opinions of
experts (Antman, 1992a)
• A decision based on the combination of critically appraised experiential,
organizational and scientific evidence yields better outcomes than a decision based
on a single source of evidence (McNees, 1990; Tetlock, 2006)
• Evaluating the outcome of a decision has been found to improve both
organizational learning and performance, especially in novel and non-routine
situations (Anseel, Lievens, & Schollaert, 2009; Ellis & Davidi, 2005)
Summary
We started this chapter by explaining what evidence-based practice was about —
that it involved decision-making through the conscientious, explicit and judicious use
of the best available evidence from multiple sources. By using and critically appraising
evidence from multiple sources you increase the likelihood of an effective decision.