Performance Index

Innate valence of a wide range of odors, measured using the Performance Index metric in the 4 Quadrant Chamber. Reproduced from Root et al., Nature (2014).

Performance Index is a simple transformation of lower right quadrant occupancy that normalizes to chance. Performance Index is calculated as:

	Performance Index = (Percent Lower Right Occupancy - 25) / 0.25

As such, it also measures the directionality and magnitude of the valence of a given stimulus. However, the Performance Index is a much easier format to read and visualize: aversive stimuli produce negative values, appetitive stimuli produce positive values, and neutral stimuli produce values around zero, all on a scale maximizing ease of human inference and conceptualization.

The Performance Index metric was first described for flies in Semmelhack et al., Nature (2009). The metric was introduced for mice alongside the 4 Quadrant Chamber in Root et al., Nature (2014).