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?