82 Police J. 247 (2009)
Distance Estimation Error in a Roadway Setting

handle is hein.journals/policejl82 and id is 253 raw text is: MARK STRAUSS
Ruhl Forensic, Inc., and University of Illinois at Urbana-
Champaign, Urbana, Illinois, USA
JAMES CARNAHAN
University of Illinois at Urbana-Champaign, Urbana, Illinois, USA
DISTANCE ESTIMATION ERROR IN
A ROADWAY SETTING
The purpose of this study was to determine the accuracy of the
typical adult's ability to view, then estimate, distances along a
roadway. A survey was conducted along a roadway, where 123
subjects were asked to look at, and then estimate the distance
to common objects along the roadway. The entire population
tended to underestimate distances to objects that were from 20
to 400 feet away. After none outliers were identified and
removed, the average estimation error was -23.4%. The vari-
ation in performance among individuals was extremely large,
with error extremes ranging from -96% to +71%. An analysis
of the percentage error in estimation revealed that police
performed as well as the rest of the population. The age of the
subjects and their rating of their own vision acuity made no
statistically significant difference in their average estimation
error. Males had significantly lower estimation error than
females, as did subjects who rated themselves highly with
respect to their distance estimation ability.
Keywords: distance; distance estimation error; gender dif-
ferences; observer accuracy; witness reliability
Introduction
Inaccuracies in statements and testimony can be attributed to
human error in estimation of distances. Such estimations may be
requested of accident witnesses in situations dealing with
vehicles and roadways. The purpose of this study was to deter-
mine the accuracy of the average adult's ability to view and then
estimate distances. A statistical analysis of the estimation accur-
acy for different sub-populations of the subjects (police, age,
gender, etc.) was performed. The data provide insight regarding
the reliability of stated estimated distances and provide averages
for quantifying the expected margins of error when estimations
are given. Of the participants surveyed, there were 77 males and
46 females, ranging from 18 to 73 years of age. Subjects were of
differing educational backgrounds and occupations, including
The Police Journal, Volume 82 (2009)                      247
DOI: 10.1358/pojo.2009.82.3.458

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