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  \subsection{The Liu Quasar Pair Catalogue}  The quasar pair catalogue sample used in this project is obtained from Lui et al 2011. The purpose of the Lui's selection criteria is to compile (from the SDSS) a Quasar Pair catalogue of interacting AGN pairs only. (Liu et al 2011)AGN pairs that make up the parent sample are identified optically from the spectroscopic sample of the SDSS DR7. Further selection criteria is applied to refine the parent sample to ensure the study of genuinely interacting AGN pairs rather than chance superpositions. Using line of sight (LOS) velocity differences (or offset) where LOS velocity is the velocity meausured measured  along the line of sight of an observer, and transverse separation - the projected distance within the LOS direction - rp ,Lui selects only AGN pairs that are interacting. The choice to use projected separations rp < 100h70-1 kpc to refine the sample space – remove pairs that are at low separation but are not interacting - h^-1 is the Hubble constant, which accounts for /is a measure of the expansion rate of the universe ( more details in \cite{Huchra_1992}). Lui further observes that most pairs with separation greater than 100 kpc are found to be closely separated but not interacting with one another. Selecting those with separation less than 100 kpc helps remove these points that are not a part of our sample space. It is surprising to note that 100 kpc is larger than the thresholds used in other galaxy pair studies namely (Barton et al. 2000; Ellison et al. 2008; Darg et al. 2010), but lui does not explain why 100 kpc is used as the threshold.  Lui further Justifies the use a LOS velocity offset (Δv) < 600 km s-1 as a method to further refine the desired sample space. Observing the distribution of (Δv) of AGN pairs (figure (2) provided in Liu) shows us that that most AGN pairs are found within the 300 ≲ (Δv) < 600 km s-1 interval. Even so, Lui et all further states that Δv range within which the pair is still interacting depends on the environment – there could be a chance that some data point were erroneously cut from the sample.