Predicted behaviour of the relative ratios of several α elements to iron (panel a): silicon, panel b): sulphur, panel c): calcium, panel d): titanium) with respect to the relative iron abundance in the solar neighbourhood, for Models 1 [short-dashed (red) lines], 4 [upper solid (blue) lines], and 5 [lower solid (black) lines]. Also shown are data from Cayrel et al. (2004, stars), Lai et al. (2008, open pentagons), Nissen et al. (2007, crosses), Gratton et al. (2003, upside-down triangles), Caffau et al. (2005, triangles), Reddy et al. (2006, filled squares), Reddy et al. (2003, open squares), and Bensby et al. (2005, filled circles). See the electronic edition of the journal for a colour version of this figure.