DiD with the three treated states

[Taiba Chau]

I was wondering how I would adjust my model where there would be 3 treatment states. There is the untreated but the treated is split into longer treated or less treated. What I mean by this is that the treatment occurs in the 6th year and continued into the 7th year. But there is another type of treatment in which it was introduced in the 7th year. My original model was:

This is showing that there was only two treatment, treated and untreated. The data is for 7 years and of which the treatment occurs in the 6th and 7th years.

I am wondering how I would change this so that there are now three treatment groups, untreated, longer treated and less treated. Which the treatment occurs in the 6th year and continues for some individuals. And for other individuals, the treatment occurs in the 7th year. Any help?

[Taiba Chau]

I forgot to include this but so far I tried writing the model as:

Where U is for the untreated, LO stands for being treated for longer, so in 6th and 7th year and then LE standard for being treated for less, so only in the 7th year

[Jared Greathouse]

You want an interrupted time series model. Look up the itsa command by Ariel Linden