Table 4.

Final model (Model C) fixed-effect parameters.

i	${\mathit{x}}_{\mathbf{i}}^{(\mathbf{j})}$	B i	SE(Bi)	β i	SE(βi)	c i	SE(ci)
0	Intercept	6.287	0.585	NA	NA	−5.393	0.502
1	Beep-track accuracy	−8.448	0.611	−1.217	0.088	7.247	0.524
2	Displacement direction	0.671	0.130	NA	NA	−0.576	0.112

Notes. i is a generic index. ${\mathrm{x}}_i^{(j)}$ denotes the ith element of vector x^(j) (equation (3)), and corresponds to the ith item feature. B_i denotes the unstandardised regression coefficient for the corresponding fixed effect in the mixed-effects logistic regression model. SE(B_i) denotes the standard error associated with the estimation of B_i, and analogous definitions hold for SE(β_i) and SE(c_i). β_i denotes a partially standardised logistic regression coefficient, where standardisation is achieved by multiplying the unstandardised coefficient by the standard deviation of the predictor variable. c_i denotes the ith element of vector c (equation (3)), and identifies the contribution that item feature $x_i^{(j)}$ makes to item difficulty. $x_2^{(j)}$ (displacement direction) is coded with 1 denoting ‘behind-the-beat’ and 0 denoting ‘before-the-beat’.