GlassRI 03: Test for a 'match' between the refractive indices of recovered and control 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.

Use a t-test to test whether there is a significant difference (at 95%) between the means of the recovered and control samples. You will need to calculate the appropriate pooled standard deviation.

What are the implications of your result in respect of a possible 'match' between the recovered and control samples?


Video Answer: As GlassRI02, s' = 4.4210-05, tSTAT = -1.68, Match