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I've developed an orthogonal design for an unlabelled experiment, however the results show an S-estimate of zero. How do I resolve this?

Design
; alts = optionA* , optionB* , optionC* , optionD*
; rows = 16
; block = 4
; orth = seq
; model:
U( optionA ) = btraveltime * tt[1,2,15,26] +
bfare * fare[1865,1900,860,690] +
bdelay * delay [3,6,44,78] +
bdirect.dummy * direct [0,1] +
bwifi.dummy * wifi [0,1] /
U( optionB ) = btraveltime * tt + bfare * fare +
bdelay * delay + bdirect * direct + bwifi.dummy * wifi /

U( optionC ) = btraveltime * tt + bfare * fare +
bdelay * delay + bdirect * direct + bwifi.dummy * wifi /

U( optionD ) = btraveltime * tt + bfare * fare +
bdelay * delay + bdirect * direct + bwifi.dummy * wifi
$

Sample size estimates can only be calculated if non-zero priors are specified. Your priors are all equal to zero. Note that sample size estimates are only meaningful if prior parameter values are reasonably reliable.

For more information about the calculation of sample size estimates:
Rose, J.M. and M.C.J. Bliemer (2013) Sample size requirements for stated choice experiments. Transportation, Vol. 40, No. 5, pp. 1021-1041.

Michiel

Thank you