Geneticist Dean Hamer has suggested that a particular allele of the SLC18A2 gene correlates with spirituality using data from a smoking survey, which included questions intended to measure "self-transcendence". Hamer performed the spirituality study on the side, independently of the National Cancer Institute smoking study. His findings were published in the mass-market book The God Gene: How Faith Is Hard-Wired into Our Genes. Hamer himself notes that SLC18A2 plays at most a minor role in influencing spirituality. Furthermore, Hamers claim that the SLC18A2 gene contributes to spirituality is controversial. Hamers study has not been published in a peer-reviewed journal and a reanalysis of the correlation demonstrates that it is not statistically significant.