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tokens: ) as well as the line and continuum fluxes using the normalization to the maximum continuum ( right ). The spectra cover ∼8 yr in the QSO rest frame. The shading of the markers indicates the progression of time. The first epoch available (SDSS, MJD 52200) is represented by the light blue marker in the centre of the plot. The initial rise in the continuum is to the epoch of maximum continuum (top right). The gradient of this response is approximately unity. In the next spectrum the continuum has collapsed, and the line has also almost disappeared (bottom left corner). When the continuum rises again, the gradient is considerably steeper. Figure 10. Left : The changing Mg ii line flux in J022556. The high cadence of observations for this object allows us to track the line flux as the continuum falls and rises over the course of ∼8 yr in the QSO rest frame. Right : The Mg ii line fluxes normalized to the maximum continuum. The epochs of the spectra are indicated with the colour, increasing chronologically from light to dark. This plot is based on the normalization of the fluxes to the epoch of maximum continuum. A 1:1 response is indicated with the dashed grey line. The initial increase in line flux is matched approximately 1:1 by the Mg ii line. Following a collapse in line and continuum, however, the gradient of the line responsivity is considerably steeper as the continuum recovers. The epoch-dependent responsivity visible in J022556 (and J002311) indicates that the scatter around the responsivity functions (in Figs 5 and 6 ) could be the result of sampling the varying objects at different stages during the BLR response to the continuum. The response of the line to the continuum does not follow a single gradient for the same object; therefore, we can expect considerable scatter around any linear response function fitted to a large ensemble. 5.3 The iBE A final measure for the responsivity is the iBE, which measures the change in EW compared to the change in continuum luminosity for individual objects. For the full population sample, the iBE is calculated as ΔEW/Δ L 2798 for each spectral pair. For the supervariable sample, the same is done for each chronologically sequential pair. The results for the full population sample are shown in Fig. 11 . Figure 11. A histogram of the intrinsic Baldwin effect for the full population sample. The number of spectral pairs, N , and the sample average, μ, are listed in the top right corner. The iBE is calculated as ΔEW/Δ L 2798 for each pair. Although there are some strong outliers, the distribution is clearly centred around −0.5. This is significantly lower than the slope of the ensemble BE of −0.16 calculated for the data from Shen et al. ( 2011 ). The distribution is largely symmetric and centred around a slope of −0.5. For the supervariable sample, the average slope is −0.54. Unfortunately, there are no literature values of the Mg ii iBE to compare these results to. For other UV lines such as C iv λ1549