Download CSI Bite Mark Learning Task

MATH II UNIT 1: STATISTICS AND DATA ANALYSIS
BITE MARK ANALYSIS
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BITE-MARK STUDY COULD BOLSTER USE AS EVIDENCE
By Brandy Benedict
Originally published in the Milwaukee Journal Sentinel
It's commonly believed that no two sets of human teeth are alike. Chips, jagged edges, crooked
teeth and gaps all contribute to a person's unique smile.
It seems reasonable, then, that bite patterns made by those teeth should be as unique as the
teeth themselves, though this has not been scientifically proven.
Now, a team of researchers at Marquette University has gotten one step closer.
By measuring the position and rotation of individual teeth from hundreds of bite samples
collected from volunteers, the researchers can statistically estimate how often the
characteristics of a particular bite pattern occur in the population and determine the
probability of someone else having the same characteristics.
The researchers ultimately hope that the scientific analysis of the patterns will provide a more
objective basis for analysis and comparison of bite-mark evidence in criminal trials.
"This project will put science behind the impression that a person's pattern of bites is unique,"
said Thomas Radmer, assistant professor and director of oral and maxillofacial surgery at
Marquette.
L. Thomas Johnson, adjunct professor at Marquette University's School of Dentistry, explained
that while intuition may say that each set of teeth would make a distinct bite pattern, there is
no scientific database proving it.
So Johnson and Radmer decided to create one.
During a two-year period they collected more than 400 bite patterns from male volunteers ages 18
to 44, the demographic most likely to be the aggressors in violent crimes involving biting.
Each subject bit down on a copper-coated wax wafer, simultaneously capturing the indentations of
his top and bottom teeth. The copper coating on the wafer ensured that the bite marks would show
up clearly when scanned into a computer.
For each sample they measured six characteristics: tooth width; degree of rotation of a tooth;
inward or outward displacement; arch width; spaces between teeth; and any missing or extra teeth.
Measurements of each bite mark pattern initially were taken by hand and had to be checked for
consistency.
"This is not an exact science; it's a bit subjective," Johnson said. "There has to be a human
mind and eye to compare."
Now, a computer can do all the hard work and get it right every time.
Thomas Wirtz, director of the dental informatics program at Marquette, developed a computer
program to measure the bite pattern characteristics automatically, eliminating any errors in
measurement.
His program looks at every pixel in the image to locate the positions of all the teeth, and then
uses formulas to calculate distances and angles.
It takes 15 to 20 minutes to measure a sample by hand, but Wirtz's computer program can do it in
about 10 seconds, a huge improvement considering the researchers ultimately would like to build a
database of tens of thousands of samples. "Without the automated program it would be a monumental
task," Radmer said.
CONTROVERSIAL AS EVIDENCE
Bite marks have a controversial history as evidence in criminal trials. First brought up as
forensic evidence in 1870, bite marks did not formally gain legal credibility in the U.S. courts
until 1954. Since then, bite-mark evidence has been used in a number of cases, most famously to
convict serial killer Ted Bundy.
But occasionally forensic dentists have been known to make some costly mistakes.
In April 2002, DNA evidence freed Ray Krone, dubbed the "snaggletooth killer," who spent 10 years
in an Arizona prison, including two on death row, based solely on incorrectly analyzed bite
marks.
Bite-mark patterns can vary wildly in clarity, and like a bruise, they can change over time. The
quality of a bite mark also depends on the substance a person has bitten, as bite marks on gum or
Styrofoam cups can be more defined than bite marks on skin. The force of the bite, the angle of
the bite and the area bitten can all affect the appearance of a bite mark.
Forensic dentists apply their expertise to formulate an opinion on whether the accused could have
made the particular bite mark patterns.
But the subjective nature of bite-mark analysis and interpretation has been the focus of harsh
criticism, and forensic dentistry has been called a "junk science."
"False convictions leave bite marks with a black eye," said Donald Simley, a certified forensic
dentist based in Madison. The study "should help the whole science of bite-mark evidence."
Radmer agreed: "The defense attorneys have been taking aim at this type of evidence in jury
trials as being subjective, not objective."
'WORTHWHILE' STUDY
With statistics to back up professional opinion, the researchers hope to make bite-mark forensics
more scientifically sound.
"What the Marquette study is trying to do is provide an objective, reliable basis to answer the
critics," said Daniel Blinka, a professor in the Marquette Law School and legal consultant for
the study. "It has a broader significance in providing a template for other areas of forensic
expertise, like fingerprint and handwriting analysis, to look to and follow."
Wirtz's computer program could be adapted to measure the width of tire treads, or width of ridges
in a fingerprint. "There are multiple applications throughout the field of forensics," Radmer
said.
The study was funded with a nearly $110,000 grant from the National Institute of Justice through
the Midwest Forensic Resource Center, part of the Ames Laboratory Research Center at Iowa State
University. The researchers expect to complete their study by Sept. 30 and will present results
in February at the annual meeting of the American Academy of Forensic Science in Washington, D.C.
The researchers agreed that the pilot study shows there is some predictability and provides a
basis for further studies.
"We've shown with a very high confidence level that the (bite) pattern is unique," Radmer said.
Johnson, too, is pleased with the results: "I think it was worthwhile."
Through the use of statistics, and using our class as a sample, we will perform our own bite mark
analysis.
BITE MARKS
 Firmly bite into your Styrofoam piece leaving an impression of your teeth. Be sure to label
your piece with your name.
 Take each of the following measurements in cm using your ruler. Round any decimals to the
nearest tenth of a centimeter. Record your measurements in the table.
 Measure the distance between
the canine teeth in cm. Measure
from the center of the tooth
mark.
 Measure the distance between
the 2nd molars in cm. Measure
from the center of the tooth
mark.
 Measure the distance, in cm,
from between the front incisors
to the line connecting the 2nd
molars. Measure from the
center of the tooth mark.
 Assign someone in your group to enter your data into the online spreadsheet.
Name
Gender Student
/ Adult
Canine
Molar
Incisor to
Molar
 Pool the class data. Find the mean and standard deviation of each dot plot. Make 6 dot
plots of the class distribution. Put your mean in the middle of the distribution. Describe the
shape of the distribution.
Construct each of the dot plots below.
Distance between canines (males)
Distance between canines (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
Distance between molars (males)
Distance between molars (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
Distance between incisors and molars (males)
Distance between incisors and molars (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
The dot plots can be created using Fathom or TI-Nspire or a frequency histogram can be created using TI-83/84. Refer to
your data in your table.
TI-83/84:
1) First it will be helpful to turn on additional diagnostic information in your
calculator.
CATALOG
SCROLL DOWN TO DianosticOn
…….…
2) Press
. (This just resets the list menus)
3) Press
4) If there is OLD data already in the lists that needs to be cleared
press the up arrow,
,
to highlight L1 and then press
to clear out the old data. Do the same for L2 if it has
OLD data that needs to be cleared.
5)
Enter the ratios of each member of your class in L1.
6)
Go to the STAT PLOT menu by pressing
cursor to the
and press
To clear out OLD
data, first highlight
L1 and press
CLEAR, ENTER.
. Move the
. Move the cursor to
and press
.
7) Finally press
and then press
.
TI-Nspire:
1) Start a New Document and Select “Add Lists & Spreadsheet”
2) Title the first column “MS” (male student) and type in all of the data in the first column.
3) Next, press the
button and select Data►6:Quick Graph.
4) You may need to drag the x-axis a bit to see the distribution appropriately.
 In either of the distributions what seems to be the ‘center’ of the data?
Extension:
Each student should gather impressions from at least two adults (21 and older) and return to class with
the data measurements. If possible, gather data from a male and a female.
As a class, the adult data will be pooled and compared with the student data.
Distance between canines (males)
Distance between canines (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
Distance between molars (males)
Distance between molars (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
Distance between incisors to molars (males)
Distance between incisors to molars (females)
Mean: _________ Standard Deviation: ____________
Mean: _________ Standard Deviation:____________
Conclusions:
1. Compare the means and standard deviations of the following groups:

Male students and female students

Adult males and adult females

Adult males and male students

Adult females and female students
2. What overall conclusions can you make from the above comparisons?
Comparing Random Samples: Now, collect data from other Math II classes completing the same
activity.
1. How do the means and standard deviations compare between all of the random samples?
2. What factors might contribute to a difference in the results?
Forensics
Retrieved from: On-line Study Guides – Bitemarks (Originally published in Forensic Dentistry On-line)
Teeth are often used as weapons when one person attacks another or when a victim tries to ward
off an assailant. It is relatively simple to record the evidence from the injury and the teeth for
comparison of the shapes, sizes and pattern that are present. However, this comparative analysis is
often very difficult, especially since human skin is curved, elastic, and distortable. In many cases,
though, conclusions can be reached about any role a suspect may have played in a crime. Forensic
odontologists can learn a lot about the victims and suspects by analyzing any bite marks that were
discovered as evidence. Bite marks can be helpful in excluding someone as a suspect, or
determining that the suspect could be the one who inflicted the bite.
At a crime scene, the victim was found with a distinct bite mark on his forearm. A bite mark sample
was collected from 5 possible suspects. The primary suspect is a female because of the
measurements that were taken. Can you decide which of the possible suspects are females? What
factors could contribute to a more specific conclusion?