DANIELLE DUFFEKLINDSEY SYKES
Law and Order:The Body in the Bag
One Late Spring Morning…
Discovery of stuffed, well-worn, and heavily stained bag
Inside of bag unidentifiable victimAuthorities called, resulting in investigation
RACE
Race of offender Race of victim
White Black OtherTOTAL
White 3,017 501 44 3,562
Black 226 2,864 8 3,098Other 47 26 122 195Unknown 33 21 2 56
TOTAL 3,323 3,412 176 6,911
SEX
Sex of offender
Sex of victim
Male Female UnknownTOTAL
Male 4,417 499 71 4,987
Female 1,754 185 23 1,962
Unknown 49 7 19 75
TOTAL 6,220 691 113 7,024
What Type of Probability to Use?
Empirical or Relative Frequency Probability The ratio of the number of times an event has
occurred to the total number of trials performed P(A) = the # of times A occurs / N
Multiplication Rule Describes the probability of one event (A) AND
another event (B)
P(A and B)= P(A)*P(B)
Victim
Race: White: 3,562/6,911 = .5154 or 51.5% Black: 3,098/6,911 = .4483 or 44.8% Other: 195/6,911 = .0282 or 2.8% Unknown: 56/6,911 = .0081 or .81%
Sex Male: 4,987/7,024 = .7099 or 71% Female: 1,962/7,024 = .2793 or 27.9% Unknown: 75/7,024 = .0107 or 1.1%
Victim Profile
What is your best prediction of the race and sex of the victim? Explain your reasoning.
White Male
Offender
Race: White: 3,323/6,911 = .4808 or 48.1% Black: 3,412/6,911 = .4937 or 49.4% Other: 176/6,911 = .0254 or 2.5%
Sex Male: 6,220/7,024 = .8855 or 88.6% Female: 691/7,024 = .0983 or 9.8% Unknown: 113/7,024 = .0160 or 1.6%
Offender Profile
What is your best prediction as to the race and sex of the offender? Explain your reasoning.
Black Male
Joint Profile
How likely is it that the victim and the offender are of the same race? Same gender? Does this agree with your preliminary predictions above?
Joint Calculation of Race
WV/WO: 3017/3562 * 3017/3323 = .7690 or 76.9%
WV/BO = .1244 or 12.4%
WV/OO = .2117 or 21.2%
BV/WO = .0049 or .49%BV/BO = .0612 or 6.1%BV/OO = .0033 or .33%
OV/WO = .0034 or .34%
OV/BO = .0018 or .18%
OV/OO = .0027 or .27%
UV/WO = .0058 or .58%
UV/BO = .0036 or .36%
UV/OO = .0066 or .66%
Joint Calculation of Sex
MV/MO: 4417/4987 * 4417/6220 = .6289 or 62.9%
MV/FO = .6396 or 64%MV/UO = .5565 or 55.7%FV/MO = .2508 or 25.1%FV/FO = .2381 or 23.8%FV/UO = .1810 or 18.1%UV/MO = .0051 or .51%UV/FO= .0066 or .66%UV/UO= .1098 or 11%
Joint Calculation Summary
Race: 76.9% Probability White Victim and White Offender
Sex: 64% Probability Male Victim and Female Offender
Does NOT agree with previous probability calculations
Conclusion
We were told the victim was white female with blonde hair
Our data shows the victim being a white male
If you were in our situation, how would you conclude the victim profile?
Profile for OFFENDER
Murder Charge on a BLACK MALE for killing a white male whose body was dumped in the river
If you have any information concerning this person please contact your local FBI office. Thank you.
Thank you!
Any Questions?