Figure 4

Class-level Bias z-score \(z_{u}^{c_{u}}\). Distribution of class-level biased z-scores as the function of socioeconomic classes. Distributions are shown for each socioeconomic class with their median values as blue points for Houston (Fig. 4(a)), New York (Fig. 4(b)), and San Diego (Fig. 4(c)). Z-score values corresponding to unbiased cases are shown with red solid lines. Positive z-score values signal an upward visiting bias characterising each city. For results on other cities see Section C and Fig. 8 in the Additional file 1