Cumulative Sum (CuSum)
methods were developed for monitoring industrial production (Page 1954, 1961). They
track changes in a variable of interest relative to a baseline value.
Levin and
Kline (1985) modified Page's CuSum method for
use in temporal analysis of epidemiological
data. The
modified CuSum monitors the pattern of disease over time in group-level data (case and population-at-risk
counts).
The CuSum accumulates deviations from a baseline disease occurrence over time. It allows rapid measurement of change from historical case counts. The statistic magnifies small, abrupt changes. Only when the CuSum exceeds a chosen threshold, used to create an "indifference zone", is the value added to the running cumulative sum. Small rises in disease occurrence do not register, limiting the chance for false positives.
Although Levin and Kline used the single maximum CuSum value in the analysis as their test statistic, ClusterSeer finds and tests the three highest CuSum values.
Levin and Kline use the modified CuSum to examine the pattern of spontaneous abortion, or miscarriages, in the first 7 months of pregnancy as reported by a New York City hospital over five years. They looked for patterns of fetal chromosomal anomalies in the data. The pattern of spontaneous abortion was not significantly different from the baseline for fetuses with chromosomal anomalies. For those with normal chromosomes, there were significant patterns in the data, with a rise in the frequency of spontaneous abortions of chromosomally normal males during the study. The authors do not speculate on what caused the increase in spontaneous abortion of males.
