I can't succed in combining dotplot graphs: I have there distinct groups of observations, marked with different colours.

dotplot ln_IGG if IGG!=. & dose==2 & gruppo=="ospite", over(DOTPLOT) yline(3.912023) yline(6.9077553) color(black) /// name(graph1, replace)
dotplot ln_IGG if IGG!=. & dose==1 & gruppo=="ospite", over(DOTPLOT) yline(3.912023) yline(6.9077553) mfcolor(white) mlcolor(black) /// name(graph2, replace)
dotplot ln_IGG if IGG!=. & (dose==0 & pregresso==1) & gruppo=="ospite", over(DOTPLOT) yline(3.912023) yline(6.9077553) mfcolor(gray) mlcolor(black) /// name (graph3, replace)

I tried with the following ...
graph combine graph1 graph2 graph3, common
... but it doesn't work!


Thanks for any kind help.

Mario Saugo
UOSD Epidemiologia
ULSS 7 Veneto
Italy