Understanding -values and significance.

values combined with estimates of effect size are used to assess the importance of experimental results. However, their interpretation can be invalidated by selection bias when testing multiple hypotheses, fitting multiple models or even informally selecting results that seem interesting after observing the data. We offer an introduction to principled uses of -values (targeted at the non-specialist) and identify questionable practices to be avoided.

Depicting variability and uncertainty using intervals and error bars.

Variability is inherent in most biological systems due to differences among members of the population. Two types of variation are commonly observed in studies: differences among samples and the "error" in estimating a population parameter (e.g.