GlassRI 04: Calculation of likelihood ratio from recovered glass fragments
 

Assume that five fragments have been recovered from a suspect's upper clothing approximately 2 hrs after a breaking incident. These fragments have RI values (each the average of several GRIM measurements) given by:

 

1.52428

1.52419

1.52430

1.52420

1.52427

 

Six control samples submitted have RI values of

 

1.52419

1.52421

1.52414

1.52422

1.5242

1.52426

 

which have a mean value = 1.52420 and standard deviation = 3.9310-05


Group the recovered samples "by eye" and check the validity of the grouping by calculating the value
l*  for the SKM2 algorithm. Use the standard deviation of the control as an estimate for the standard deviation of the recovered group.
Hint: See tutorial question GlassRI 02 for the same calculation.

Apply the required test for a match between recovered and control fragments.
Hint: See tutorial question GlassRI 03 for the same calculation.

Calculate the likelihood ratio for obtaining the evidence given the competing hypotheses that the suspect was involved in breaking the window and that the accumulation of glass on his clothes occurred purely by chance.

Formulate your statement.
 

Video Answer: As GlassRI02 and GlassRI03, L = 10,000