The original reconstruction of proto-Palaihnihan suffered from poor quality data. David Olmsted's dictionary depends almost entirely upon de Angulo, who did not record the phonological distinctions consistently or well, and carelessly includes Pomo vocabulary from a manuscript in which he (de Angulo) set out to demonstrate that Achumawi and Pomo are not related.William Bright has also pointed out problems with Olmsted's methods of reconstruction. The reconstruction is being refined with newer data.
The Palaihnihan family is often connected with the hypothetical Hokan stock. Proposed special relationships within Hokan include Palaihnihan with Shastan (known as Shasta-Achomawi) and within a Kahi sub-group (also known as Northern Hokan) with Shastan, Chimariko, and Karuk.
^Hammarström, Harald; Forkel, Robert; Haspelmath, Martin, eds. (2017). "Palaihnihan". Glottolog 3.0. Jena, Germany: Max Planck Institute for the Science of Human History.
^Gursky, Karl-Heinz (1987). "Achumawi und Pomo, eine besondere Beziehung?". Abhandlungen der völkerkundlichen Arbsgemeinschaft. Nortorf. 57.
^Bright, William; Olmsted, D. L. (1965). "Review of A history of Palaihnihan phonology by D. L. Olmstead". Language. Baltimore: Linguistic Society of America. 41 (1): 175–178. doi:10.2307/411871. JSTOR411871.
Bright, William; Olmsted, D. L. (1965). "[Review of A history of Palaihnihan phonology by D. L. Olmstead]". Language. 41 (1): 175–178. doi:10.2307/411871. JSTOR411871.
Good, Jeff; McFarland, Teresa; & Paster, Mary. (2003). Reconstructing Achumawi and Atsugewi: Proto-Palaihnihan revisited. Atlanta, GA. (Paper presented at the annual meeting of the Society for the Study of the Indigenous Languages of the Americas, January 2–5).
Nevin, Bruce E. (1991). "Obsolescence in Achumawi: Why Uldall Too?". Papers from the American Indian Languages Conferences, held at the University of California, Santa Cruz, July and August 1991. Occasional Papers on Linguistics 16:97-127. Department of Linguistics, Southern Illinois University at Carbondale.
Nevin, Bruce E. (1998). Aspects of Pit River phonology. Ph.D. dissertation, University of Pennsylvania.
Olmstead, David L. (1954). "Achumawi–Atsugewi non-reciprocal intelligibility". International Journal of American Linguistics. 20 (3): 181–184. doi:10.1086/464275.