The primary purpose of research is to estimate the magnitude and direction of effects which exist “out there” in the real world. An effect may be the result of a treatment, a trial, a decision, a strategy, a catastrophe, a collision, an innovation, an invention, an intervention, an election, an evolution, a revolution, a mutiny, an incident, an insurgency, an invasion, an act of terrorism, an outbreak, an operation, a habit, a ritual, a riot, a program, a performance, a disaster, an accident, a mutation, an explosion, an implosion, or a fluke.

I am sometimes asked, what do researchers do? The short answer is that we estimate the size of effects. No matter what phenomenon we have chosen to study we essentially spend our careers thinking up new and better ways to estimate effect magnitudes. But although we are in the business of producing estimates, ultimately our objective is a better understanding of actual effects. And this is why it is essential that we interpret not only the statistical significance of our results but their practical, or real-world, significance as well. Statistical significance reflects the improbability of our findings, but practical significance is concerned with meaning. The question we should ask is, what do my results say about effects themselves?

Interpreting the practical significance of our results requires skills that are not normally taught in graduate-level Research Methods and Statistics courses.