Accuracy v Precision

This week we're going to touch a bit on the concepts of accuracy and precision.

In biomedical science, we're usually measuring outcomes that nobody has every measured before in quite the same way (and probably never will measure them again!)

As a consequence, we rarely have any sense about how accurate our results are. To know accuracy, we'd have to know what the "true" value in a population we've sampled for some outcome variable . That truth is usually elusive.

So most of the time the best we can do is estimate precision. As we move into the statistics of measured data, the standard error of the mean (sem) is the statistic that we use for assessing precision. The lower the sem, the greater then precision.

I'm omitting from the slide deck this year one of my favorite pics that illustrates wonderfully how the battle for greater accuracy and improved precision plays out over time.

This graph is from the Particle Data Group at the Lawrence Berkely Lab. The pdf that has 11 other graphs much like it. This one shows the evolution of the mass of the eta particle, over time.

For over 20 years the mass was one value. Since then, the mass value has bounced around quite a bit. The most current estimate of the mass appears very precise.

But is it accurate?

The true mass of these eta has remained the same, while the accuracy and precision by which it is measured continues to fluctuate.