Variability index V in the u, g, r, and i band (left to right) versus luminosity for the 23 WLQs identified in the variability catalogue (filled red squares, magenta frames: WLQ-EWS subsample). For comparison, the entire sample from the variability catalogue is indicated by the median relation (thick blue curve) with standard deviation (shaded green area) and by the equally spaced logarithmic local point density contours (estimated with a grid size of Δx,Δy = 0.2,0.2). Open circle with error bars: mean value and 1σ deviations of the WLQs.