st: bivariate probit problem with no (0,0) observations

[Pierre Lafaye de Micheaux <plafaye@club-internet.fr>]

Dear Stata gurus,

Here is the experiment we are conducting:

Laboratory rats are smelling some kind of odour and then we measure 
their neuronal activity. We then observe the presence/absence of gamma 
or beta waves.
But you should always have some kind of wave (beta or gamma). The 
absence of the two waves means a failure in the experiment.
So you only have (1,1), (1,0) and (0,1) data.
And never (0,0) data. (But when the rat is dead, or the electrod badly 
placed, etc ...).

We are interested in modeling the presence/absence of gamma or beta 
waves as a function of odour's characteristics.

We then wanted to use a bivariate probit analysis (through biprobit for 
example) but the fact that there is no (0,0) observations (structural 
zero case) seems to be a problem.

Do you know how we could handle this?

Best regards,

Pierre

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/