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STR Data Analysis and Interpretation for Forensic Analysts

Analysis Modes

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As previously mentioned, there are two analysis modes (classic Macintosh and advanced Windows NT modes). The differences between these modes are found in the sizing method and the flexibility of peak sensitivity settings.

Specifically the mode differences are:

  • In the classic mode, size calling is performed by matching the actual size standard fragments of the sample with a defined size standard that must be accurately labeled; it utilizes scan number to assign sizes.
  • In the advanced mode, size calling is performed using a function known as "ratio matching." Ratio matching uses an algorithm to determine the distance between the size fragments based on the entry of a set of size fragment values, where it uses the relative distance between the neighboring peaks to size.

The following excerpts from the Applied Biosystems User Bulletin on Size Parameters explain these differences.05

Peak identification with GeneScan analysis software for the Macintosh operating system
National Institute of Justice (NIJ) (see reuse policy).
Peak identification with the GeneScan analysis software for the Windows NT operating system
National Institute of Justice (NIJ) (see reuse policy).

There are similarities between GMID and GS/GT software. However, GMID offers additional features, added flexibility, and efficiency through the combining of the programs. The expert system potential, inherent in the software, will continue to develop as new versions are released.


To become familiar with the use of GMID 3.2, it is recommended that analysts read through the User's Manual for v3.1 and User Bulletin for v3.2; focusing particular attention on the verification process and the software features and functions.07

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