**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 = 3.93×10^{-05}

Group the recovered samples "by eye" and check the validity of the grouping by calculating the value l

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*' =
4.42×10^{-05},
*t*_{STAT} = -1.68, Match