Table 5.
Instrumental Variable Modeling Examining AFE to Tackle Football and Age of Symptom Onset in Tackle Football Players with and without CTE
| Cognitive Symptom Onset | |||
|---|---|---|---|
| Unstandardized beta (S.E.) |
t-test statistic (p-value) |
95% CI | |
| CTE+ | |||
| Per year increase in AFE | 2.44 (0.41) | 6.02 (<0.0001) | 1.63, 3.25 |
| AFE<12 | 13.39 (2.44) | 5.49 (<0.0001) | 8.58, 18.20 |
| CTE Only |
Unstandardized
beta (S.E.) |
t-test
statistic (p-value) |
95% CI |
| Per year increase in AFE | 2.93 (0.51) | 5.70 (<0.0001) | 1.92, 3.94 |
| AFE<12 | 16.38 (3.16) | 5.19 (<0.0001) | 10.11, 22.64 |
| CTE− | |||
| Per year increase in AFE | 1.27 (2.17) | 0.58 (0.57) | −3.24, 5.78 |
| AFE<12 | 20.33 (10.33) | 1.97 (0.063) | −1.15, 41.81 |
| Behavioral/Mood Symptom Onset | |||
| Unstandardized beta (S.E.) |
t-test
statistic (p-value) |
95% CI | |
| CTE+ | |||
| Per year increase in AFE | 2.50 (0.46) | 5.44 (<0.0001) | 1.59, 3.41 |
| AFE<12 | 13.28 (2.77) | 4.79 (<0.0001) | 7.82, 18.74 |
| CTE Only | Unstandardized beta (S.E.) |
t-test
statistic (p-value) |
95% CI |
| Per year increase in AFE | 2.66 (0.55) | 4.87 (<0.0001) | 1.57, 3.75 |
| AFE<12 | 13.16 (3.41) | 3.86 (0.0002) | 6.40, 19.92 |
| CTE− | |||
| Per year increase in AFE | 2.49 (1.48) | 1.68 (0.11) | −0.57, 5.55 |
| AFE<12 | 22.42 (6.94) | 3.23 (0.0037) | 8.06, 36.78 |
AFE = Age of first exposure. Duration of play was included as a covariate and decade at age 12 served as the instrument variable, where the instrument assumes that it is associated with age of cognitive and behavioral mood symptom onset only through its effect on AFE. The instrumental variable model is a two-stage regression. The first stage estimated the effect of decade at age 12 on AFE. In the second stage, predicted values from the association between decade at age 12 and AFE in the first stage were used to predict age of cognitive and behavioral/mood symptom onset. Example of parameter estimate interpretation: For CTE+ participants, every one year younger participants started to play tackle football predicted earlier symptom onset by 2.44 and 2.50 years for cognitive and behavioral/mood symptom onset, respectively. AFE before age 12 was associated with onset of cognitive symptoms by 13.39 years earlier, and behavioral/mood symptoms by 13.28 years earlier.