The Visual Display

The problem with tirne-series is that the simple passage of time
not a good cxplanatory variable: descriptive chronology is not
expianation. There arc occasional cxceptions, especially when
is a clear mech:nism rh:t drives rhe Y-variable. This timedoes
testiE rbout causality: the outgoing mail ofthe U.S.
ofRepresentatives peaks every two years,jusr before the
dav:
grapbic is worth ar leasr 7oo wo'd:, the number used ir a
report describing how incumbenr reprerenrariva exploit their
mailing privileges to advance thei re-election campaiqns:
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