The Stability Of g With Time

The cross-time correlation asymptotes at r = +0.9

I got ahold of this paper, and the abstract sharply undersells the strength of the paper’s results. When the initial testing period happens at 20 years old, the reliability-corrected effect (across all cognitive abilities) asymptotes at 0.9 [p.24]. Moreover, meta-analytic effects were not corrected for attrition-related range restriction:
https://not-equal.org/content/pdf/misc/2024-51553-001.pdf

This is a problem because low-IQ people are more likely to die:
https://sci-hub.ru/https://doi.org/10.1093/ije/dyq190
This means that in long-term retest studies, the sample of people you get in old age will have been smarter than average when they were younger and will have been less variable at the time too due to that range restriction. Morevoer, the more open-minded participants will also be more likely to agree to participate in studies like this, and such people will be more intelligent too, thereby compounding the problem. The reduced standard deviation among study participants will mean that even if the absolute amount of similarity in intelligence across time remains constant, the correlation coefficient will be reduced.

Correcting for range restriction alone, one study comparing people at 11 and 80 years old found that the correlation went from .63 and .66 to .73:
https://sci-hub.ru/https://doi.org/10.1037/0022-3514.86.1.130

They also did moderator analyses for what abilities were captured, and for effect sizes using better measures of g, the raw asymptote was a bit higher at .792. This is in spite of the effects using better measures of g being disadvantaged WRT the age + interval moderators (see supplementary table S2 in the docx linked below):
https://not-equal.org/content/publicationSupplements/BUL-2022-0996_Supplemental_Materials.docx

For retesting interval, the mean period for g was 6.75 years while it was 6.52 years when all abilities were lumped together For age at pre-test, the mean age for g was 12.03 years while it was 18.07 years when all abilities were lumped together: