Link Above. If I have the correct one, this is one of the studies mentioned in the Kris Pope "Coyote Trapping School" podcast, Episode 54:

ABSTRACT
in Central Oregon. The scent station
index remained relatively constant at a mean value of 0. 025 from
May through mid-August; increased to a mean value of 0. 043 in
September; then decreased to a mean of 0. 038 in October. Reduced
scent effectiveness due to weathering was not evident. Between-line
and within-line variability of the index remained relatively constant
throughout the study period. Between-line variability accounted for
more of the total variation in indices than between-month variability.
Up to four-fold, statistically significant, differences in index values
between lines were evident throughout the study. The mean percent
of coyotes that scored at a scent station, once they were on a segment
of the road surface that extended 30 feet on each side of a scent post,
was 28.8 percent over all lines and periods. There was statistically
Redacted for Privacy
significant variation in the percent scoring between lines and this
variation partially explained the between-line differences for the scent
station index. The percent scoring did not change significantly
between months, however. An alternate index in which the stations
read were 60 foot long segments of the road surface at 0. 3 mile
intervals was found to give an approximate four-fold increase in mean
indices and a significant reduction in coefficient of variation cornpared
to the standard scent station index. The relative merits of
these two indices were compared. A functional relationship between
coyote numbers, coyote activity and index values was proposed and
evaluated in terms of observed index values. Seasonal capabilities
of the index as a research tool were evaluated in terms of seasonal
variability and the pattern of mean indices obtained throughout the
study.