Concept in spatial data analysis
The Greenwood statistic is a spacing statistic and can be used to evaluate clustering of events in time or locations in space. 
Definition.
In general, for a given sequence of events in time or space the statistic is given by:.
formula_1
where formula_2 represents the interval between events or points in space and is a number between 0 and 1 such that the sum of all formula_3. 
Where intervals are given by numbers that do not represent a fraction of the time period or distance, the Greenwood statistic is modified and is given by:
formula_4
where:
formula_5
and formula_6 represents the length of the "'i"th interval, which is either the time between events or the distances between points in space.
A reformulation of the statistic yields
formula_7
where formula_8 is the sample coefficient of variation of the "n" + 1 interval lengths.
Properties.
The Greenwood statistic is a comparative measure that has a range of values between 0 and 1. For example, applying the Greenwood statistic to the arrival of 11 buses in a given time period of say 1 hour, where in the first example all eleven buses arrived at a given point each 6 minutes apart, would give a result of roughly 0.10. However, in the second example if the buses became bunched up or clustered so that 6 buses arrived 10 minutes apart and then 5 buses arrived 2 minutes apart in the last 10 minutes, the result is roughly 0.17. The result for a random distribution of 11 bus arrival times in an hour will fall somewhere between 0.10 and 0.17. So this can be used to tell how well a bus system is running and in a similar way, the Greenwood statistic was also used to determine how and where genes are placed in the chromosomes of living organisms. This research showed that there is a definite order to where genes are placed, particularly with regard to what function the genes perform, and this is important in the science of genetics.
References.
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