problem with ITSA multiple group

[parastou amirifar]

Hi. According to the Linden article about ITSA https://www.researchgate.net/profile...ication_detail,page 484, in ITSA multiple group analysis, The key assumption is that the change in the level or trend in the outcome variable is presumed to be the same both for the
control group and, counterfactually, for the treatment group had it not received the intervention. If we have only one control group and this key assumption does not apply, do we have to change our model? If yes, which model do you recommend?
Best regards
P.A.