Mean detection probability of the 632 targets with more than one RV in our sample as a function of orbital period, including 7 additional targets from Maxted et al. (2000b) that satisfy the SPY survey criteria. Dips in efficiency at e.g. P = 1 d correspond to typical time intervals between exposures. The calculations were based on the assumption that the visible white dwarf has a mass of 0.55 M_⊙ and companion masses of 0.05 (brown dwarf), 0.20 (ELM), 0.55 (typical white dwarf) and 0.85 M_⊙ (Chandrasekhar mass system) as indicated on the plot.