Mean fire interval [Mean fire-free interval]
n. An arithmetical index of fire frequency, expressed as the average number of fire intervals within a given time period.
Although the median value is typically a more accurate measure of central tendency, the mean is also useful, particularly when only two fire intervals are available for analysis. Because that situation occurs relatively frequently when sampling fire history, the mean fire interval (MFI) statistic has been used more often than the median fire interval. However, the potential utility of the MFI statistic is diminished if only few data are available for analysis, or, when the fire intervals are highly variable. For further discussion, see Agee (1993), McPherson and others (1990), and Romme (1980).