We have generated a series of composite QSO spectra using over 22000 individual low resolution ( \sim 8 Å ) QSO spectra obtained from the 2dF ( 18.25 < b _ { J } < 20.85 ) and 6dF ( 16 < b _ { J } \leq 18.25 ) QSO Redshift Surveys .
The large size of the catalogue has enabled us to construct composite spectra in relatively narrow redshift ( \Delta z = 0.25 ) and absolute magnitude ( \Delta M _ { B } = 0.5 ) bins .
The median number of QSOs in each composite spectra is \sim 200 , yielding typical signal-to-noise ratios of \sim 100 .
For a given redshift interval , the composite spectra cover a factor of over 25 in luminosity .
For a given luminosity , many of the major QSO emission lines ( e.g .
Mg II \lambda 2798 , [ O II ] \lambda 3727 ) can be observed over a redshift range of one or greater .

Using the composite spectra we have measured the line strengths ( equivalent widths ) of the major broad and narrow emission lines .
We have also measured the equivalent width of the Ca II \lambda 3933 K absorption feature due to the host galaxy of the AGN .
Under the assumption of a fixed host galaxy spectral energy distribution ( SED ) , the correlation seen between Ca II K equivalent width and source luminosity implies L _ { gal } \propto L _ { QSO } ^ { 0.42 \pm 0.05 } .
We find strong anti-correlations with luminosity for the equivalent widths of [ O II ] \lambda 3727 and [ Ne V ] \lambda 3426 .
These provide hints to the general fading of the NLR in high luminosity sources which we attribute to the NLR dimensions becoming larger than the host galaxy .
This could have important implications for the search for type 2 AGN at high redshifts .
If average AGN host galaxies have SEDs similar to average galaxies , then the observed narrow [ O II ] emission could be solely due to the host galaxy at low luminosities ( M _ { B } \sim - 20 ) .
This suggests that the [ O II ] line observed in high luminosity AGN may be emitted , in a large part , by intense star-forming regions .
The AGN contribution to this line could be weaker than previously assumed .

We measure highly significant Baldwin effects for most broad emission lines ( C IV \lambda 1549 , C III ] \lambda 1909 , Mg II \lambda 2798 , H \gamma , H \beta ) and show that they are predominantly due to correlations with luminosity , not redshift .
We find that the H \beta and H \gamma Balmer lines show an inverse Baldwin effect and are positively correlated with luminosity , unlike the broad UV lines .
We postulate that this previously unknown effect is due to a luminosity dependent change in the the ratio of disk to non-disk continuum components .