GE HEALTHCARE Biacore T100, Handbook

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9 Kinetics and affinity analysis
9.4 Quality assessment for kinetics evaluation
168
Biacore T100 Software Handbook BR-1006-48 Edition AE
9.4.2 Statistical parameters
Two statistical parameters are provided to help in assessing the results:
• Chi-squared is an indicator of how closely the fitted curves agree with the
experimental data. One chi-squared value is reported for the whole fitting.
• Standard error or T-value is an indicator of parameter significance, and is
reported separately for each fitted parameter.
Chi-squared
Chi-squared is a measure of the average squared residual (the difference
between the experimental data and the fitted curve), calculated as:
For sensorgram data, the number of data points is very much larger than the
number of fitted parameters in the model, so
and chi-squared reduces to the average squared residual per data point. If the
model fits the experimental data precisely, chi-squared represents the mean
square of the signal noise.
Chi-squared is listed on the Report tab.
Standard error and T-value
The significance of parameter values is indicated by the standard error (SE) or T-
value listed on the
Parameters tab in the fitting results. This is a statistical
indication of the significance of a fitted parameter. Lower standard error values
indicate higher significance: if the standard error represents less than 10% of
the parameter value, the parameter is significant for the experimental data.
For ease of comparison between parameters with widely different absolute
values (e.g. k
a
and k
d
), the standard error may be expressed as a T-value , which
is obtained by dividing the value of the parameter by the standard error. A high
where r
f
is the fitted value at a given point
r
x
is the experimental value at the same point
n is the number of data points
p is the number of fitted parameters
chi-squared
r
f
r
x
–
( )
2
1
n
∑
n p
–
----------------------------
=
n p n
≈
–