Blust 1991:78-79
Greater Central-Philippine Hypothesis
Oceanic Linguistics XXX[30].2.

In a large, still unpublished study first reported in Blust (1981b), it was found that Ilongot has the lowest basic vocabulary retention rate of any of the 25 Philippine languages tested to date. From this fact alone it can be concluded that its lexicostatistical percentages with other languages are deflated, and hence will produce a misleading impression of great divergence from other languages than history would warrant. [fn4]. I concur with Z86 that Ilongot probably is a Southern Cordilleran language.

Footnote 4 [page 106]
The figure obtained for Kakidugen Ilongot is 68/199 = 34.2%. An even lower retention percentage (26.9) has since been obtained for Arta (Reid 1989:48)