In contrast to fluctuating asymmetry, directional asymmetry is systematic, i.e. across the population it is systematically more often in one direction than in the other. It means that across the population a deviation is more often to one direction than to the other, i.e., there is a statistically significant bias to one direction. In case of directional asymmetry, most individuals of a species are asymmetric to the same side, even though some individuals can be symmetric, or even asymmetric to the opposite side (cf., e.g., handedness). The relation between directional and fluctuating asymmetry is comparable to the concepts of accuracy and precision in empirical measurements.