Bio-Rad Image Lab™ Software - Manual (Page 203)

User Guide | 203
E Regression Calculation
Methods
Each regression method calculates a standard curve. Some of the methods provide
the formula for the standard curve. In this case, the molecular weight can be
calculated by:
x = relative front of the band of interest
y = molecular weight of the band of interest
Linear (semilog): The linear equation is y = a + bx, where a is the intercept and b is
the slope of the line.
Note: The linear equation is calculated on the log of the molecular weight
values.
The R
2
value can be used to determine the overall quality of the linear fit. A linear
regression with an R2 value of >0.99 is considered a very good fit. The primary
advantage of this method is that it is extremely simple. The primary disadvantage is
that it will deliver incorrect results if the data are not very linear.
Point-to-point (semilog): No single equation is available for the point-to-point
method. The slope of each segment of the curve between data points is calculated
independently.
Note: The log of the molecular weight values is used to calculate the slope for
each segment of the curve.
Logistic: The logistic-4PL equation is