I have this semi-cross over study design. It can be depicted as two different groups - control and treatment. Patients are initially randomized into either control or treatment group. The control group received placebo in the first 12 months, then received treatment in the next 12 months, and then received the same treatment in another 12 months. The treatment group received treatment for the first 12 months, and then same treatment for the next 12 months then stops.
Control group: [Period 1: Placebo][Period 2: Tx]*[Period 3: Tx]* Treatment group: [Period 1: Tx][Period 2: Tx]*
*No blinding of assigned treatment/control during this period.
What would be the most appropriate statistical testing for this study design, assuming the outcome is average biochemical level (in numeric value).