Paired samples are the two samples of the observations with the characteristic feature with each of the observation in one sample have only one matching observation in the other sample. There are several techniques in which such samples can occur in the medical investigations. The first, self- pairing, happens when each subject serves as his or her own control, as in, for instance, therapeutic trials in which each of the subjects receives both the treatments, one on each of two separate occasions. Consequently, natural-pairing can occur particularly, for instance, in laboratory experiments involving litter-mate controls. Lastly artificial pairing might be taken in use by the investigator to match the two subjects in the pair on significant characteristics likely to be related to response variable.