Wesonga, Ronald, et al. “Modelling Airport Efficiency With Distributions Of The Inefficient Error Term: An Application Of Time Series Data For Aircraft Departure Delay”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 12, no. 1, Nov. 2013, pp. 115-23, https://gssrr.org/JournalOfBasicAndApplied/article/view/1229.