FAQ  Frequently Asked Questions
Issue:

How do I calculate my own T^{2} and Q limits?
Possible Solutions:

Confidence limits for Q residuals (also known as "SPE") and Hotellings T^{2} can be calculated using the commands:
residuallimit tsqlimTo calculate new residual limits, you must pass the eigenvalues for the residuals from the model. Assuming you have a model structure named "model":
qlimit = residuallimit(model.detail.reseig,cl);where
cl
is the confidence limit desired (in fractional confidence limit: 0.95 ). Note that for some model types, .detail.reseig
is not defined. In these cases, you'll need to calculate the raw residuals themselves. You can usually do this with datahat, but you need to pass the original calibration data along with the model:
[xhat,residuals] = datahat(model,data); qlimit = residuallimit(residuals,cl);To calculate new T^{2} limits, tsqlim can be called very simply:
tsqcl = tsqlim(m,pc,cl);where
m
is the number of samples in the model, pc
is the number of PCs (or LVs) in the model, and cl
is the confidence limit desired.
Note that tsqlim supplies the same result whether cl is a percent or fractional but residuallimit requires the a fraction cl.
To calculate limits for individual scores, see the related FAQ.
Still having problems? Check our documentation Wiki or try writing our helpdesk at helpdesk@eigenvector.com