While acknowledging that FST remains useful, a number of scientists have written about other approaches to characterizing human genetic variation. Long & Kittles (2009) stated that FST failed to identify important variation and that when the analysis includes only humans, FST = 0.119, but adding chimpanzees increases it only to FST = 0.183. Mountain & Risch (2004) argued that an FST estimate of 0.10–0.15 does not rule out a genetic basis for phenotypic differences between groups and that a low FST estimate implies little about the degree to which genes contribute to between-group differences. Pearse & Crandall 2004 wrote that FST figures cannot distinguish between a situation of high migration between populations with a long divergence time, and one of a relatively recent shared history but no ongoing gene flow. In their 2015 article, Keith Hunley, Graciela Cabana, and Jeffrey Long (who had previously criticized Lewontin's statistical methodology with Rick Kittles) recalculate the apportionment of human diversity using a more complex model than Lewontin and his successors. They conclude: "In sum, we concur with Lewontin's conclusion that Western-based racial classifications have no taxonomic significance, and we hope that this research, which takes into account our current understanding of the structure of human diversity, places his seminal finding on firmer evolutionary footing."