2. Data and methods
The data used in this study are derived from two
separate data sets of Penal Code offenses that
occurred in the central 23 wards of Tokyo and
recorded by the TMPD, as shown in Table 1. The
first data set was recorded using the older recording
system and covers the period of calendar year 2001
(namely, from January 1 to December 31). The
second data set was recorded using the newer
recording system and covers the period of Japanese
fiscal year 2001 (namely, from April 1 to March 31).
In the analyses that follow, we focused on the offenses
that occurred during the 9-month period between
April 1 and December 31, because these offenses were
recorded in both of the above two data sets..