The Scan Method (Wallenstein, 1980,1987) tests for temporal clustering in single and several time series with group-level data. Use the Scan test with case counts, not rates. The data can be relatively sparse or numerous. The time series must be at least five time cells in length.
The test is biased by changes in population size through time, which can cause significance even when underlying clustering is absent. You can analyze several time series at once using time series files containing several series. However, the P-values for each series will not be combined to yield an overall P-value.
Example
Wallenstein and Neff (1987) used the method to test whether there was temporal clustering in spontaneous abortions (due to trisomy) in New York City during the 1970s.
