In order to compare different spiral galaxies, a secure sample of spirals must first be defined. The sample is defined by selecting galaxies with pfeatures × pnotedge-on × pspiral > 0.5. A further cut is also imposed where only galaxies with Nspiral−Ncan′ttell≥5Nspiral−Ncan′ttell≥5N_\mathrm{spiral} - N_\mathrm{can^{\prime }t \, tell} \ge 5 are selected, meaning that at least five people classified the spiral arm number of each of the spiral galaxies, reducing the effects of noise due to low numbers of classifications
Spiral sample selection