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Home My WebLink AboutICPD 2015 Traffic Stop AnalysisICPD TRAFFIC STOP ANALYSIS ICPD STOP MAP THE NUMBER OF STOPS BY ZONE 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 57 60 64 Percents For Department N =12850 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 57 60 64 Percents Days N = 3650 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 57 60 64 Percents Nights N = 9200 TRAFFIC OBSERVATIONS TRAFFIC OBSERVATIONS 2007-2015 2015 traffic observations = 27,032 2007-2012 traffic observations = 28,951 Total traffic observations = 55,983 2015 OBSERVATIONS—WE FOCUSED ON ZONES WHERE MOST STOPS WERE MADE Zone 21 traffic observations = 11,880 Zone 29 traffic observations = 8,114 Other zones traffic observations = 7,038 Spread over zones 27, 28, 30 and 38 Observations made from 9/01/15 through 2/28/16 OBSERVATION RESULTS Previous traffic stop observations and 2010 Census Bureau data suggest that about 10% of the drivers on the roads in most areas of Iowa City are minority drivers—both days and nights. 2015 traffic observations are mostly consistent with this finding, except for the following areas. ZONE 21 DAYS (DOWNTOWN AREA) ZONE 21 NIGHTS (DOWNTOWN AREA) ZONE 29 DAYS (BROADWAY AREA) ZONE 29 NIGHTS (BROADWAY AREA) ZONE 30 DAYS & NIGHTS ZONE 28 DAYS & NIGHTS A WORD ABOUT THE BENCHMARKS Please keep in mind that roadside observations are simply a sample of the drivers on the roads. As such, the values indicated in the results should be treated as estimates with a fairly generous confidence interval  DAYS 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 57 60 64 Percents Days N = 3650 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 13 20 21 22 27 28 29 30 Percent of Minority Drivers Stopped--Days percent minority stopped days benchmark AVERAGE DISPARITY ACROSS ZONES  The highest degrees of disproportionality is concentrated in areas where the fewest stops were made A disparity index shows that the average degree of disproportionality across all areas of town was approximately five percentage points higher than the corresponding benchmark values. The index gives a ballpark estimate of disproportionality. Zone 27 Days race Freq. Percent Cum. Asian/Pacific Islander 16 7.02 7.02 Black/African American 39 17.11 24.12 Caucasian 164 71.93 96.05 Latino/Hispanic 3 1.32 97.37 Other 5 2.19 99.56 Unk 1 0.44 100.00 Total 228 100.00 Zone 27 Days Zone 28 days race Freq. Percent Cum. Asian/Pacific Islander 12 4.29 4.29 Black/African American 60 21.43 25.71 Caucasian 189 67.50 93.21 Latino/Hispanic 10 3.57 96.79 Other 5 1.79 98.57 Unk 4 1.43 100.00 Total 280 100.00 Zone 28 Days Zone 30 Days race Freq. Percent Cum. Asian/Pacific Islander 7 2.69 2.69 Black/African American 66 25.38 28.08 Caucasian 164 63.08 91.15 Latino/Hispanic 17 6.54 97.69 Native American/Indian 2 0.77 98.46 Other 3 1.15 99.62 Unk 1 0.38 100.00 Total 260 100.00 Zone 30 Days NIGHTS 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 57 60 64 Percents Nights N = 9200 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 13 20 21 22 27 28 29 30 Percent of Minority Drivers Stopped -- Nights percent minority stoppednights benchmark AVERAGE DISPARITY ACROSS ZONES  The highest degrees of disproportionality is concentrated in areas where the fewest stops were made A disparity index shows that the average degree of disproportionality across all areas of town was approximately five percentage points higher than the corresponding benchmark values. The index gives a ballpark estimate of disproportionality. Zone 20 Nights race Freq. Percent Cum. Asian/Pacific Islander 56 11.43 11.43 Black/African American 90 18.37 29.80 Caucasian 302 61.63 91.43 Latino/Hispanic 28 5.71 97.14 Other 8 1.63 98.78 Unk 6 1.22 100.00 Total 490 100.00 Zone 20 Nights Zone 27 Nights race Freq. Percent Cum. Asian/Pacific Islander 14 6.73 6.73 Black/African American 46 22.12 28.85 Caucasian 129 62.02 90.87 Latino/Hispanic 3 1.44 92.31 Native American/Indian 1 0.48 92.79 Other 10 4.81 97.60 Unk 5 2.40 100.00 Total 208 100.00 Zone 27 Nights Zone 28 Nights race Freq. Percent Cum. Asian/Pacific Islander 61 10.30 10.30 Black/African American 105 17.74 28.04 Caucasian 360 60.81 88.85 Latino/Hispanic 36 6.08 94.93 Other 19 3.21 98.14 Unk 11 1.86 100.00 Total 592 100.00 Zone 28 Nights Zone 30 Nights race Freq. Percent Cum. Asian/Pacific Islander 20 5.08 5.08 Black/African American 92 23.35 28.43 Caucasian 250 63.45 91.88 Latino/Hispanic 26 6.60 98.48 Native American/Indian 1 0.25 98.73 Other 2 0.51 99.24 Unk 3 0.76 100.00 Total 394 100.00 Zone 30 Nights OFFICER LEVEL ANALYSIS DISPARITY INDEX (% Minority / Min. Benchmark) ÷ (% W&A / W&A Benchmark) 0 2 4 6 8 Fr e q u e n c y 0 2 4 6weighted_index Disparity Index 𝑥 = 1.71 z2 = 3.54 OUTCOMES ODDS-RATIOS Compares the values of two ratios (Minority-yes/Minority-no) ÷ (White-yes/White-no) Values > 1 suggest disproportionality WARNINGS no yes Total minority 545 2,340 2,885 white 1,437 8,400 9,837 Total 1,982 10,740 12,722 OR = 0.73 CITATIONS no yes Total minority 2,371 514 2,885 white 8,420 1,417 9,837 Total 10,791 1,931 12,722 OR = 1.28 ARRESTS no yes Total minority 2,612 273 2,885 white 9,342 495 9,837 Total 11,954 768 12,722 OR = 1.97 SEARCH REQUESTS no yes Total minority 2,688 197 2,885 white 9,488 349 9,837 Total 12,176 546 12,722 OR = 1.99 HITS no yes Total minority 142 55 197 white 255 94 349 Total 397 149 546 OR = 1.05 -1.4 -1.5 -1.2 1.2 1.4 1.4 1.6 1.5 1.3 2005 2006 2007 2010 2011 2012 2013 2014 2015 citations 2.54 2.82 2.61 3.08 3.18 2.55 2.33 2.05 1.97 2005 2006 2007 2010 2011 2012 2013 2014 2015 arrests 2.54 3.42 5.62 2.75 3.89 2.44 1.93 1.51 1.99 2005 2006 2007 2010 2011 2012 2013 2014 2015 search requests -1.6 1.2 -2.9 -2.3 -1.3 -1.2 1.1 -1.1 1.05 2005 2006 2007 2010 2011 2012 2013 2014 2015 hit rates SUMMARY Results suggest a degree of racial disproportionality in traffic stops conducted by the ICPD. A ballpark estimate of the level of disproportionality indicates that minority drivers were stopped on average about five percentage points higher than the observation benchmark values. Comparatively little traffic stop disproportionality was found in areas of town where the lion’s share of traffic stops were made. Most disproportionality occurred in areas where stops were less frequent.  Individual officer analyses show that two officers’ disparity index values were considerably higher than other officers’ values. SUMMARY  Disproportionality in most stop outcomes decreased in recent years. The single exception was citations, where disproportionality increased. It should be noted however, that odds-ratio values for citations were comparatively modest. In recent years, officers were about twice as likely to arrest a minority driver as others during a stop In recent years, officers were about twice as likely to request a voluntary search from a minority driver as from other drivers. This occurred even though seizures or hit rates resulting from voluntary searches were about the same for minority and non-minority drivers. Overall, results suggest that the levels of disproportionality in stops and outcomes is trending lower.