“…In the literature, it is also referred to as hierarchical linear modeling, mixed models, random coefficient model, and longitudinal modeling (Fitzmaurice et al 2004; Littell et al 2006; Rogosa & Saner 1995; Singer & Willett 2003; Snijders & Bosker 1999). For the current data, the model was specified hierarchically using two levels (Level-1 and Level-2), and can be expressed symbolically as the predicted intelligibility/quality score ( Y ij ) of listener i at condition j as a function of envelope fidelity ( F ij ) and as a function of hearing loss ( HFPTA i ), working memory ( RST i ), and age ( Age i ) with the following equation:
where
Equation 1 represents the Level-1 model where intercept, P 0 j , corresponds to the expected value of intelligibility/quality when F ij equals zero, and the slope, P 1i , represents the rate of change in intelligibility/quality as fidelity increases.…”