The therapeutic factor inventory-8: Using item response theory to create a brief scale for continuous process monitoring for group psychotherapy.

Objective: We tested a very brief version of the 23-item Therapeutic Factors Inventory-Short Form (TFI-S), and describe the use of Item Response Theory (IRT) for the purpose of developing short and reliable scales for group psychotherapy.
Method: Group therapy patients (N = 578) completed the TFI-S on one occasion, and their data were used for the IRT analysis. Of those, 304 completed the TFI-S and other measures on more than one occasion to assess sensitivity to change, concurrent, and predictive validity of the brief version.
Results: Results suggest that the new TFI-8 is a brief, reliable, and valid measure of a higher-order group therapeutic factor.
Conclusion: The TFI-8 may be used for continuous process measurement and feedback to improve the functioning of therapy groups.