Data for results in "Minimizing group index variations in a multicore endoscope fiber" paper. The variation in group index was measured using a low coherence scanning Mach-Zehnder interferometer utilizing a fiber-based optical supercontinuum with a 10 nm band-pass filter centered at 800 nm as a low-coherence light source. The input and output ends of the sample fiber were translated with respect to the coupling lenses in order to study different cores while maintaining the path outside of the optical fiber constant.