Hierarchical linear models improve the measurement of performance when applied to a construct such as a metroplex. It compares the outcomes of a hierarchical linear model with those of a multiple regression model to evaluate whether meteorological conditions at individual airports and overall would explain variations in block delays. The study used the cases of the three largest airports in the DC Metroplex and concluded airborne delays had a significant random effect on block delays in spite of meteorological conditions at each airport. It pointed out that surface operations efficiency played a significant role in explaining variations in block delays.
