Radio spectral index, α (where S_ν ∝ ν^α), versus spectroscopic redshift for the 35 LOFAR detected quasars overlapping with FIRST. Upper limits are given for the quasars not detected in FIRST and a lower limit is given for the quasar not detected in LoTSS. The median spectral index for the quasar sample is both determined by stacking all 93 quasars (red) and only the 35 S/N > 2 detected ones (grey) in the overlapping LoTSS and FIRST area. The red and grey areas give the errors on the median spectral indices, which are the 16th and 84th percentiles determined by bootstrapping.