Bio-Rad Gel Doc™ EZ System - Manual (Page 54)

Criterion Stain Free TM System | Designing Protocols
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If you do not have enough data points for the selected method, the molecular
weight of the unknown bands will not be calculated.
Which method to select depends on the gel type:
• 4-20% gradient gels: The Linear (semi-log) regression method
works well for these gels, since the mobility of the bands is linear to
the log of their molecular weight. As an alternative, the Point-to-
Point (semi-log) method can be used, if the r
2
value is not good
enough.
• 10% gels: These gels have a non-linear relationship between the
mobility and the molecular weight. Good choices for regression
methods are Logistic or Cubic Spline.
You can check how well each regression method fits the data in the standard
curve window (for more information, see “Standard Curve” on page 54.) The
Linear (semi-log) regression method provides a measurement which describes
how well the standard curve fits the data, r
2
value. The closer the r
2
value is to
1.0, the better the data fits the standard curve.
For information about the calculations behind the regression methods, see the
Glossary.