Table 4 Generalized additive model (GAM) parametric coefficients and significance of the smoothing terms

Parametric coefficients

Factor

Estimate

Standard error

t value

Pr ( >|t|)

Intercept

6.58

0.33

19.9

 < 2e − 16 (***)

Approximate significance of smoothing terms

Smoothing term

Edf

Ref.df

Chi.sq

p value

 s(H_ALS)

1.95

2.00

105.79

 < 2e − 16 (***)

 s(H_ALS*year)

1.87

4.00

37.88

 < 2e − 16 (***)