After some googling it seems that multicolumn support is not yet implemented in org tables. I would need multicolumn headers quite urgently, but I have not yet found a way to make this possible.
I think that tables with headers like this: | | mean | s.e. | | gender | varA | varB | varA | varB | are quite common, so I really want to put this feature on the wish list. I am not able to implement this myself. Erich