Delete attribute level balance

[KMeeuw]

I want to create a design for 4 attributes with 3 levels and 2 attributes with 2 levels.
When I look to a possible basic plan, a design would be possible with 16 choicesets.
However NGene only find a solution with 36 choicesets. I believe that this is due to the fact that Engene strives for attribute level balance.
I am wondering how I can let NGene assume NO attribute level balance. In the manual I only see instructions for ;fact or ;eff design, but not for ;orth: seq design and that is where I want to apply it.
Does anybody knows how to do this?

Here is my Ngene code which result in 36 choice sets.
design
;alts = alt1, alt2, alt3
;rows = 16
; orth = seq
;model:
U(alt1) = pl*PL[0,1,2] + pef*PEF[0,1,2] + fs*F[0,1] + br*BR[0,1] + er*ER[0,1,2] + svc*SVC[0,1,2] /
U(alt2) = pl*PL + pef*PEF + fs*FS + br*BR + er*ER + svc*SVC /
U(alt3) = pl*PL + pef*PEF + fs*FS + br*BR + er*ER + svc*SVC /
$

[Michiel Bliemer]

Orthogonal arrays are BY DEFINITION attribute level balanced. Therefore, unbalanced orthogonal arrays do not exist. If there is no need for attribute level balance, there is then likely also no need for orthogonality.

The typical way to move away from attribute level balance is by creating an efficient design. This can be easily done by setting all priors equal to zero (which you already have) and using the modified Federov algorithm (i.e., ;alg = mfederov). Using zero priors essentially creates a near-orthogonal design.