Some Error Rates Associated with Bloodstain Pattern … drop of human blood from 35 cm onto ceramic...

INTRODUCTION

MATERIALS AND METHODS

RESULTS

CONCLUSIONS

REFERENCES

•  Bloodstain  pa,ern  analysis  allows  for  the  es3ma3on  of  Area  of  Origin.  

•  Area  of  Origin  relies  on  the  calcula3on  of  angle  of  impact.  

•  Li,le  research  has  been  conducted  to  quan3tate  error  rates  associated  with  angle  of  impact  calcula3ons  (Willis  et  al.,  2001).  

•  Our  goal  was  to  inves3gate  the  effect  of  impact  angle  and  surface  texture  on  error  rate.  

•  Error  rates  increased  as  angle  of  impact  increased  (Table  1)  

•  Error  rates  <  1.2°  

•  Only  one  angle  of  impact  measured  accurately  

•  Surface  texture  had  a  significant  (P  <  0.05)  effect  on  error  rates  at  10°  and  50°  but  not  at  90°  (Table  1)  

Blood  •  Human  blood  (1.07g/mL  ±  0.003g/mL)  drawn  intravenously  into  preserva3ve  free  vials  

Surfaces  •  Three  surfaces  of  contras3ng  texture  used  (ceramic  3le,  porcelain  3le,  mirror)  

Experimental  Design  •  Tiles  placed  at  three  angles  (10°,  50°,  90°)  •  Blood  dropped  (0.03mL  ±  0.001mL)  onto  3les  from  Pasteur  pipe,e  at  height  of  35  cm  

•  Each  set  of  impact  stains  measured  by  four  individuals  varying  in  levels  of  exper3se  ranging  from  novice  to  expert  

•   Experiment  replicated  ten  3mes    

Sta7s7cal  Analyses  •  Data  did  not  meet  the  assump3ons  set  forth  for  normality  and  homogeneity  of  variance  as  determined  by  the  Kolmogorov-­‐Smirnov  test  and  Levene’s  test,  respec3vely  

•  Comparison  of  means  conducted  using  the  Kruskall-­‐Wallis  H  and  Mann-­‐Whitney  U  sta3s3cs  

•  Imposing  ±  3.5° on  50° and  90°  impact  stains  and  ±  1.9° on  10° impact  stains  made  our  AOI  calcula3ons  accurate.  

•  These  error  rates  are  smaller  than  those  currently  used  by  bloodstain  pa,ern  analysts  (Allard  et  al.,  2010).  

•  This  allows  for  more  precise  es3mates  of  area  of  origin.  

Table 1. Angle of impact estimated by four analysts ranging in experience following the drop of human blood from 35 cm onto ceramic tile, mirror tile, or porcelain tile within 3 minutes of blood leaving the body. Letters denote a significant (P < 0.05) difference between surface within angle of impact. Standard errors are presented in parentheses where n = 10.

Angles of Impact

Surfaces 10° 50° 90°

Ceramic 11.6° (0.2°)ab 53.5° (0.7°)a 88.3° (0.9°)a

Mirror 11.9° (0.1°)a 50.3° (0.6°)b 86.5° (1.2°)a

Porcelain 11.3° (0.1°)b 48.8° (0.5°)b 87.8° (1.1°)a

Figure 1: 10° impact stains on porcelain tile

Figure 2: 90° impact stains on ceramic tile

•  Allard  KL,  Kish  PE,  Gestring  BJ  (2010)  Evalua3ng  the  validity  of  angle  of  impact/incidence  determina3ons  made  from  very  small  bloodstains.  Proceedings  of  the  62nd  Annual  Mee3ng  of  the  American  Academy  of  Forensic  Sciences,  16:116.    

•  Willis,  C.,  Piranian,  A.K.,  Donaggio,  J.R.,  Barne,,  R.J.,  &  Rowe,  W.F.  (2001).  Errors  in  the  es3ma3on  of  the  distance  of  fall  and  angles  of  impact  blood  drops.  Forensic  Science  Interna.onal,  123,  1-­‐4.    

Some Error Rates Associated with Bloodstain Pattern Analysis

Kaitlin Leslie1, Taylor Lowis1, Larry E. Barksdale2, David O. Carter1 1Department of Entomology, University of Nebraska- Lincoln, 68583-0816

2Lincoln Police Department, Lincoln, Nebraska