On statistical searches for filaments

The presence or absence of an excess of filamentary structure in the galaxy distribution has important implications for the origin of such structure. In an attempt to answer this question, many statistics have been devised to quantify the visual impression of filaments seen in galaxy maps, but few of these are at all well understood. Two of these, a quadrupole elongation statistic and a nearest-neighbor alignment statistic, are analyzed in the common language of the irreducible N-point correlation functions of the galaxy distribution, and it is argued that there has as yet been no success in isolating filaments in particular from clustering in general.