Table 6.

Association between exposure measures and neurofibrillary tangle burden

	Mean increase in NFT burden per unit increase in respective measure (95% CI)	R2	p-value	BIC
Athletes with all 11 brain regions available for analysis (n = 519)
Concussion number	1.56 × 10−4 (−1.96 × 10−3−2.28 × 10−3)	0.43	0.89
Position, non-speed vs speeda	1.34 (−0.26–2.93)	0.35	0.10
Duration of play per year	0.47 (0.36–0.57)	0.49	3.8 × 10−16	3558
CHII per 1,000 hits	0.44 (0.26–0.62)	0.45	1.8 × 10−6	3602
CHII-G per 10,000 g	0.51 (0.39–0.63)	0.49	2.6 × 10−16	3557
CHII-R per 1,000,000 rad/sec2	0.52 (0.39–0.65)	0.49	7.6 × 10−15	3564

Separate linear regressions were run for each exposure measure due to multicollinearity to determine betas, R², and p-values. For models with significant exposure measures, BIC is reported to determine relative model performance. All models had the outcome of semi-quantitative NFT burden summed across 11 brain regions (0–33) and were adjusted for age at death. The sum score was based on neuropathologists semi-quantitative NFT burden on a 0–3 scale with increasing severity for 11 brain regions implicated in CTE: dorsolateral frontal cortex, middle frontal cortex, orbitofrontal cortex, hippocampus regions CA1, CA2, CA3/4, substantia nigra, amygdala, entorhinal cortex, inferior parietal cortex, and locus coeruleus. Results are presented for the 519 athletes with available tissue for all 11 brain regions

BIC Bayesian information criterion, CHII cumulative head impact index representing estimated number of head impacts per donor per 1,000 hits, CHII-G cumulative head impact index representing estimated cumulative g-force experienced by each donor per 10,000 g, CHII-R cumulative head impact index estimated cumulative rotational force experienced by each donor per 1,000,000 rad/sec², CTE chronic traumatic encephalopathy, NFT neurofibrillary tangle

^aPresented as dichotomous non-speed (offensive and defensive lineman) vs speed (all other positions) for all football players with a single known position