... Archives . ... Reduced and Processed Data . ... 2 distribution plays an incredibly important role in astronomical data analysis, but it is pretty much a black box to most astronomers. ... Comment ( RSS ) | ... I guess in the typical analysis we call chi2 a ?random variable? that follows the chi2 distribution: . ... where D(i) is the observed data, M(i) is the model predicted data and we ?silently? assume that D(i) is normally distributed and each i measurement is independent. ... Chandra Blog . ...